Optimal duration of exclusive breastfeeding

  • Review
  • Intervention

Authors

  • Michael S Kramer,

    Corresponding author
    1. McGill University Faculty of Medicine, Departments of Pediatrics and Epidemiology, Biostatistics and Occupational Health, Montreal, Quebec, Canada
    • Michael S Kramer, Departments of Pediatrics and Epidemiology, Biostatistics and Occupational Health, McGill University Faculty of Medicine, 2300 Tupper Street, Les Tourelles, Montreal, Quebec, H3H 1P3, Canada. michael.kramer@mcgill.ca.

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  • Ritsuko Kakuma

    1. The University of Melbourne, Centre for International Mental Health, Melbourne School of Population Health, Carlton, Victoria, Australia
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Abstract

Background

Although the health benefits of breastfeeding are widely acknowledged, opinions and recommendations are strongly divided on the optimal duration of exclusive breastfeeding. Since 2001, the World Health Organization has recommended exclusive breastfeeding for six months. Much of the recent debate in developed countries has centred on the micronutrient adequacy, as well as the existence and magnitude of health benefits, of this practice.

Objectives

To assess the effects on child health, growth, and development, and on maternal health, of exclusive breastfeeding for six months versus exclusive breastfeeding for three to four months with mixed breastfeeding (introduction of complementary liquid or solid foods with continued breastfeeding) thereafter through six months.

Search methods

We searched The Cochrane Library (2011, Issue 6), MEDLINE (1 January 2007 to 14 June 2011), EMBASE (1 January 2007 to 14 June 2011), CINAHL (1 January 2007 to 14 June 2011), BIOSIS (1 January 2007 to 14 June 2011), African Index Medicus (searched 15 June 2011), Index Medicus for the WHO Eastern Mediterranean Region (IMEMR) (searched 15 June 2011), LILACS (Latin American and Caribbean Health Sciences) (searched 15 June 2011). We also contacted experts in the field.

The search for the first version of the review in 2000 yielded a total of 2668 unique citations. Contacts with experts in the field yielded additional published and unpublished studies. The updated literature review in December 2006 yielded 835 additional unique citations.

Selection criteria

We selected all internally-controlled clinical trials and observational studies comparing child or maternal health outcomes with exclusive breastfeeding for six or more months versus exclusive breastfeeding for at least three to four months with continued mixed breastfeeding until at least six months. Studies were stratified according to study design (controlled trials versus observational studies), provenance (developing versus developed countries), and timing of compared feeding groups (three to seven months versus later).

Data collection and analysis

We independently assessed study quality and extracted data.

Main results

We identified 23 independent studies meeting the selection criteria: 11 from developing countries (two of which were controlled trials in Honduras) and 12 from developed countries (all observational studies). Definitions of exclusive breastfeeding varied considerably across studies. Neither the trials nor the observational studies suggest that infants who continue to be exclusively breastfed for six months show deficits in weight or length gain, although larger sample sizes would be required to rule out modest differences in risk of undernutrition. In developing-country settings where newborn iron stores may be suboptimal, the evidence suggests that exclusive breastfeeding without iron supplementation through six months may compromise hematologic status. Based on the Belarusian study, six months of exclusive breastfeeding confers no benefit (versus three months of exclusive breastfeeding followed by continued partial breastfeeding through six months) on height, weight, body mass index, dental caries, cognitive ability, or behaviour at 6.5 years of age. Based on studies from Belarus, Iran, and Nigeria, however, infants who continue exclusive breastfeeding for six months or more appear to have a significantly reduced risk of gastrointestinal and (in the Iranian and Nigerian studies) respiratory infection. No significant reduction in risk of atopic eczema, asthma, or other atopic outcomes has been demonstrated in studies from Finland, Australia, and Belarus. Data from the two Honduran trials and from observational studies from Bangladesh and Senegal suggest that exclusive breastfeeding through six months is associated with delayed resumption of menses and, in the Honduran trials, more rapid postpartum weight loss in the mother.

Authors' conclusions

Infants who are exclusively breastfed for six months experience less morbidity from gastrointestinal infection than those who are partially breastfed as of three or four months, and no deficits have been demonstrated in growth among infants from either developing or developed countries who are exclusively breastfed for six months or longer. Moreover, the mothers of such infants have more prolonged lactational amenorrhea. Although infants should still be managed individually so that insufficient growth or other adverse outcomes are not ignored and appropriate interventions are provided, the available evidence demonstrates no apparent risks in recommending, as a general policy, exclusive breastfeeding for the first six months of life in both developing and developed-country settings.

Résumé scientifique

Durée optimale de l'allaitement exclusif

Contexte

Même si les bénéfices de l'allaitement pour la santé sont largement reconnus, les avis et les recommandations divergent fortement concernant la durée optimale de l'allaitement exclusif. Depuis 2001, l'Organisation mondiale de la Santé recommande un allaitement exclusif pendant six mois. Une grande partie du débat récent dans les pays développés s'est portée sur l'adéquation des micronutriments, ainsi que sur l'existence et l'ampleur des bénéfices de cette pratique pour la santé.

Objectifs

Évaluer les effets sur la santé, la croissance et le développement de l'enfant et sur la santé de la mère de l'allaitement exclusif pendant six mois versus l'allaitement exclusif pendant trois à quatre mois avec un allaitement mixte (introduction d'aliments liquides et solides complémentaires avec la poursuite de l'allaitement) par la suite jusqu'à six mois.

Stratégie de recherche documentaire

Nous avons effectué des recherches dans The Cochrane Library (2011, numéro 6), MEDLINE (du 1er janvier 2007 au 14 juin 2011), EMBASE (du 1er janvier 2007 au 14 juin 2011), CINAHL (du 1er janvier 2007 au 14 juin 2011), BIOSIS (du 1er janvier 2007 au 14 juin 2011), African Index Medicus (recherche effectuée le 15 juin 2011), Index Medicus for the WHO Eastern Mediterranean Region (IMEMR) (recherche effectuée le 15 juin 2011), LILACS (Latin American and Caribbean Health Sciences) (recherche effectuée le 15 juin 2011). Nous avons également contacté des experts du domaine.

La recherche effectuée pour la première version de la revue en 2000 a donné un total de 2 668 références bibliographiques uniques. Les contacts établis avec des experts du domaine ont donné des études publiées et non publiées supplémentaires. La revue de la littérature mise à jour de décembre 2006 a donné 835 références bibliographiques uniques supplémentaires.

Critères de sélection

Nous avons sélectionné toutes les études observationnelles et tous les essais cliniques contrôlés en interne comparant les critères de jugement concernant l'enfant ou la mère avec un allaitement exclusif pendant six mois ou plus versus un allaitement exclusif pendant au moins trois à quatre mois avec la poursuite d'un allaitement mixte jusqu'à au moins six mois. Les études ont été stratifiées en fonction du plan d'étude (essais contrôlés versus études observationnelles), de la provenance (pays en développement versus développés) et de la durée d'allaitement dans les groupes d'alimentation comparés (trois à sept mois versus plus tard).

Recueil et analyse des données

Nous avons évalué la qualité des études et extrait des données de façon indépendante.

Résultats principaux

Nous avons identifié 23 études indépendantes répondant aux critères de sélection : 11 réalisées dans des pays en développement (dont deux étaient des essais contrôlés réalisés au Honduras) et 12 réalisées dans des pays développés (toutes des études observationnelles). Les définitions de l'allaitement exclusif étaient extrêmement diverses selon les études. Ni les essais ni les études observationnelles ne suggèrent que les nourrissons qui continuent à être exclusivement allaités pendant six mois présentent des déficiences en termes de gain de poids ou de longueur, même si des échantillons de plus grande taille seraient nécessaires pour écarter les différences modestes concernant le risque de sous-alimentation. Dans les pays en développement où les réserves en fer des nouveau-nés peuvent être sous-optimales, les preuves suggèrent qu'un allaitement exclusif sans supplémentation en fer jusqu'à six mois peut menacer les paramètres hématologiques. D'après l'étude biélorusse, un allaitement exclusif de six mois ne confère aucun bénéfice (versus allaitement exclusif de trois mois suivi par la poursuite d'un allaitement partiel jusqu'à l'âge de six mois) concernant la taille, le poids, l'indice de masse corporelle, les caries dentaires, la capacité cognitive ou le comportement à l'âge de 6,5 ans. Cependant, d'après des études réalisées en Biélorussie, en Iran et au Nigeria, les nourrissons qui poursuivent l'allaitement exclusif pendant six mois ou plus semblent présenter un risque significativement réduit d'infection gastro-intestinale et (dans les études iraniennes et nigérianes) d'infection respiratoire. Il n'a été démontré aucune réduction significative du risque d'eczéma atopique, d'asthme ou d'autres critères de jugement atopiques dans les études réalisées en Finlande, en Australie et en Biélorussie. Les données issues des deux essais honduriens et d'études observationnelles du Bengladesh et du Sénégal suggèrent que l'allaitement exclusif jusqu'à l'âge de six mois est associé à une reprise tardive des règles et, dans les essais honduriens, à une perte de poids postpartum plus rapide chez la mère.

Conclusions des auteurs

Les nourrissons qui sont exclusivement allaités pendant six mois ont une morbidité due à une infection gastro-intestinale moins élevée par rapport à ceux qui sont partiellement allaités à partir de trois ou quatre mois, et, que ce soit dans les pays en développement ou dans les pays développés, il n'a été démontré aucun retard de croissance chez les nourrissons qui sont exclusivement allaités pendant six mois ou plus. Par ailleurs, les mères de ces nourrissons ont une aménorrhée lactationnelle plus prolongée. Même si les nourrissons doivent encore être surveillés individuellement de façon à ne pas ignorer les croissances insuffisantes ou les autres critères de jugement indésirables et à proposer des interventions adéquates, les preuves disponibles ne démontrent aucun risque apparent à recommander un allaitement exclusif pendant les six premiers mois, dans le cadre d'une politique générale, tant dans les pays en développement que dans les pays développés.

Resumo

Duração ideal do aleitamento materno exclusivo

Introdução

Embora os benefícios da amamentação para a saúde sejam amplamente reconhecidos, existem controvérsias em relação a qual deveria ser sua duração ideal. Desde 2001, a OMS recomenda o aleitamento materno exclusivo até os 6 meses de vida. Recentemente, tem havido muitos debates em países desenvolvidos quanto a essa prática, tendo sido levantadas questões quanto à adequação dos micronutrientes fornecidos ao bebê, assim como à existência e à magnitude dos benefícios dessa recomendação.

Objetivos

Avaliar os efeitos do aleitamento materno exclusivo por 6 meses versus aleitamento materno exclusivo por 3-4 meses seguido de amamentação mista (introdução de líquidos ou alimentos sólidos associado com a amamentação) até o 6º mês, sobre o crescimento e desenvolvimento da criança e sobre a saúde materna.

Métodos de busca

Foram realizadas buscas nas seguintes bases de dados eletrônicas: Cochrane Library (Issue 6, 2011), MEDLINE (de 1 de janeiro de 2007 até 14 de junho de 2011), EMBASE (de 1 de janeiro de 2007 até 14 de junho de 2011), CINAHL (de 1 de janeiro de 2007 até 14 de junho de 2011), BIOSIS (de 1 de janeiro de 2007 até 14 de junho de 2011), African Index Medicus (15 de junho de 2011), Index Medicus for the WHO Eastern Mediterranean Regions (IMEMR) (15 de junho de 2011), LILACS (15 de junho de 2011). Também foram contatados especialistas sobre o tema.

Para a primeira versão desta revisão publicada em 2000, a busca encontrou 2668 citações únicas. O contato com especialistas acrescentou mais estudos publicados e não publicados. A atualização da busca em dezembro de 2006 acrescentou mais 835 citações exclusivas.

Critério de seleção

Foram selecionados todos os ensaios clínicos controlados internamente e os estudos observacionais que compararam desfechos de saúde infantil ou materno em grupos de aleitamento materno exclusivo por pelo menos 6 meses versus aleitamento exclusivo por pelo menos 3-4 meses seguido de aleitamento misto até pelo menos 6 meses. Os estudos foram estratificados quanto ao seu desenho (ensaios clínicos versus estudos observacionais), origem (países em desenvolvimento e desenvolvidos), e época de avaliação dos desfechos (3-7 meses versus mais de 7 meses de vida).

Coleta dos dados e análises

Revisores independentes avaliaram a qualidade dos estudos e realizaram a extração de dados.

Principais resultados

Foram identificados 23 estudos que preenchem os critérios de seleção: 11 oriundos de países em desenvolvimento (sendo 2 estudos controlados em Honduras) e 12 de países desenvolvidos (todos estudos observacionais). As definições de aleitamento exclusivo variaram bastante entre os estudos. De acordo com os ensaios clínicos e com os estudos observacionais, as crianças em aleitamento exclusivo por 6 meses não apresentam maiores riscos de déficit de peso ou comprimento, embora amostras maiores seriam necessárias para descartar pequenas diferenças no risco de desnutrição. Em países em desenvolvimento onde os recém-nascidos podem ter depósitos de ferro abaixo do ideal, a evidência sugere que o aleitamento materno exclusivo sem suplementação de ferro até o 6º mês de vida pode comprometer os parâmetros hematológicos dos bebês. Baseado no estudo da Bielorrússia, o aleitamento materno exclusivo por 6 meses (versus aleitamento exclusivo por 3 meses seguido por aleitamento parcial até o 6º mês) não confere nenhum beneficio em termos de estatura, peso, índice de massa corporal (IMC), cáries dentárias, habilidade cognitiva ou comportamental avaliados com 6,5 anos de idade. Porém, segundo os achados dos estudos da Bielorrússia, Irã e Nigéria, as crianças que continuam com amamentação exclusiva por pelo menos 6 meses tem uma redução significativa do risco de infecções gastrointestinais e (segundo os estudos iranianos e nigerianos) de infecções respiratórias. Segundo os estudos da Finlândia, Austrália e da Bielorrússia, o aleitamento exclusivo não reduz de forma significativa o risco de eczema atópico, asma ou outras atopias. Segundo 2 estudos de Honduras e estudos observacionais de Bangladesh e do Senegal, o aleitamento exclusivo por 6 meses está associado a um período mais longo de amenorreia e, segundo os estudos de Honduras, a uma perda de peso materno pós-parto mais rápida.

Conclusão dos autores

Crianças em aleitamento materno exclusivo por 6 meses tem menos morbidade decorrente de infecções gastrointestinais do que aquelas que são parcialmente amamentadas a partir do 3º-4º mês de vida. Crianças de países desenvolvidos ou em desenvolvimento que são amamentadas exclusivamente no peito por 6 ou mais meses não apresentam nenhum déficit de crescimento. Além disso, as mães dessas crianças ficam mais tempo sem menstruar. Cada bebê deve ser avaliado individualmente para que sejam detectadas deficiências de crescimento ou outros problemas que necessitem de intervenções adequadas para cada caso. Porém, as evidências disponíveis indicam que não existe nenhum risco aparente em se recomendar, como norma geral, que todos os bebês sejam amamentados exclusivamente no peito durante os primeiros 6 meses de vida, tanto nos países desenvolvidos como em desenvolvimento.

摘要

完全純母乳餵食的最佳期間

背景

雖然餵食母乳對健康的好處是大家所公認的,但是對於完全純母乳餵食所建議的最佳期間,意見卻是非常分歧。自從2001年以來,世界衛生組織建議純母乳餵食期間為6個月。在這種作法之下,最近大部分的爭論在許多已開發國家主要在於微量營養素是否足夠,如同對於健康有益的重要性爭論一樣。

目的

為了評估對兒童的健康、生長、發育和對產婦健康的影響,以純母乳餵食6個月以及純母乳餵食3至4個月後再混合餵食(以補充液體或是固體食物混合母乳)直到6個月為止,兩組作為比較。

搜尋策略

我們搜索了The Cochrane Library (2011年第6期)、MEDLINE (2007年1月1日到2011年6月14日)、EMBASE (2007年1月1日到2011年6月14日)、CINAHL (2007年1月1日到2011年6月14日)、African Index Medicus (2011年6月15日)、IMEMR (2011年6月15日)、LILACS (2011年6月15日) 等資料。我們也聯繫了這個領域的專家。

在2000年的回顧中,第一個版本的搜索產生了2668個引用文章,與該領域的專家聯繫取得了其他已發表以及未發表的研究,在2006年12月最新的文獻回顧得到了835個額外的引用文章。

選擇標準

我們篩選了所有內部控制的臨床試驗和觀察研究,比較以純母乳餵養6個月或是更久與純母乳餵食至少3至4個月後再混合餵食至少到6個月這兩組兒童或是產婦健康的結果。研究層次是根據研究的設計 (對照試驗與觀察研究),來源 (發展中國家與已發展國家),以及比較餵食組別的時間 (3到7個月與之後的)。

資料收集與分析

我們獨立評估研究的質量與獲取的資料。

主要結果

我們確認了23個獨立的研究符合篩選標準: 11個來自發展中國家 (其中2個為來自宏都拉斯的對照試驗組),12個來自已開發國家 (全部均為觀察研究組)。純母乳餵食的定義在各研究之中有很大的不同。不管是試驗組或是觀察組的研究均沒有顯示出,嬰兒接受純母乳餵食6個月會造成體重不足或身長不足,儘管樣本數需要再增加以避免營養不足的風險造成些許的差異。在發展中國家組別,新生兒對於鐵質的儲存可能不是很理想,證據顯示出純母乳餵食6個月而沒有補充鐵質可能會危害到血液的狀態。根據白俄羅斯的研究,純母乳餵食6個月對於身高、體重、身體質量指數 (BMI)、齲齒、認知能力、或是到6歲半的行為,均未有益處 (與純母乳餵食3個月後再以部分母乳餵食至6個月相比);然而根據白俄羅斯、伊朗、奈及利亞的研究,新生兒接受純母乳餵食6個月以上可以顯著降低腸胃道以及呼吸道感染的風險 (伊朗與奈及利亞的研究)。從芬蘭、澳洲、白俄羅斯的研究則證明,沒有顯著減少對於過敏性濕疹、氣喘、或其他過敏症狀的風險。從兩個宏都拉斯試驗組與孟加拉、塞內加爾的觀察組,資料顯示純母乳餵食6個月與產婦月經恢復遲緩有關,於宏都拉斯試驗組,產婦在產後體重快速的下降。

作者結論

新生兒接受純母乳餵食6個月與部分母乳餵食3或4個月比較,有較少的腸胃道感染發病率,也沒有生長不足的證據,不管是在發展中國家或是已開發國家的新生兒,已開發國家的新生兒則以純母餵食6個月或更久。此外,這些嬰兒的母親則有更長的哺乳期閉經。雖然新生兒應該被以單獨個案管理,以免忽略生長不足或是其他不良的結果,並提供適當的介入,在一般的政策下,無論是生活在發展中或是已開發國家的環境,以純母乳餵食前6個月,現有的證據並未證實有明顯的風險。

アブストラクト

完全母乳哺育の至適期間

背景

母乳哺育の健康上の利益は広く認識されているが、完全母乳哺育の至適期間に関する意見および勧告ははっきりと分かれている。2001年以降、世界保健機関(World Health Organization)は6ヵ月間の完全母乳哺育を推奨している。先進諸国での最近の議論の多くは、完全母乳哺育の場合、微量栄養素が十分であるか、健康上の利益の範囲と大きさがどのくらいかという点に集中している。

目的

生後6ヵ月間の完全母乳哺育を、生後3~4ヵ月間の完全母乳哺育とその後生後6ヵ月までの混合栄養の併用(母乳栄養を継続しながら補充の流動食または固形食を導入する)と比較し、児の健康、成長および発達、ならびに母体の健康への効果を評価すること。

検索戦略

コクラン・ライブラリ(2011年第6号)、MEDLINE(2007年1月1日~2011年6月14日)EMBASE(2007年1月1日~2011年6月14日)、CINAHL(2007年1月1日~2011年6月14日)、BIOSIS(2007年1月1日~2011年6月14日)、African Index Medicus(2011年6月15日検索)、Index Medicus for the WHO Eastern Mediterranean Region (IMEMR)(2011年6月15日検索)、LILACS (Latin American and Caribbean Health Sciences)(2011年6月15日検索)を検索した。 本分野の専門家にも連絡を取った。 2000年の最初のレビューの検索により、総計2,668件の重複しない文献を得た。本分野の専門家との連絡で、その後追加された発表/未発表の研究を得た。2006年12月の文献更新検索で835件のその後追加された重複しない文献を得た。

選択基準

6ヵ月以上の完全母乳哺育を、3~4ヵ月以上の完全母乳哺育と生後6ヵ月以上まで継続の混合母乳栄養の併用とを比較し、小児または母体の健康アウトカムを検討しているすべての内部比較臨床試験および観察研究を選択した。研究デザイン(比較試験 vs 観察研究)、研究地(ローリソース国 vs 先進国)、栄養群比較時期(3~7ヵ月 vs それより後)によって研究を層別化した。

データ収集と分析

レビューアが別々に試験の質を評価し、データを抽出した。

主な結果

選択基準を満たす23件の独立した研究を同定した。11件はローリソース国(うち2件はホンジュラスの比較試験)で、12件は先進国(すべて観察研究)からのものであった。完全母乳哺育の定義は研究間で大幅に異なっていた。いずれの試験、観察研究も、6ヵ月の完全母乳哺育を継続した乳児の体重、身長の成長度が劣っていると示唆しなかったが、低栄養のリスクにおける軽微な差を除外するにはより大きなサンプル・サイズが必要であった。新生児の鉄貯蔵が最適以下のローリソース国の状況では、鉄補充のない6ヵ月間の母乳哺育により血液学的状態が低下することが示唆される。ベラルーシの研究に基づくと、6ヵ月間の完全母乳哺育は(3ヵ月間の完全母乳哺育とその後6ヵ月まで部分的母乳哺育を継続する混合哺育に比べて)、6.5歳時の身長、体重、体格指数、う歯、認知能力、行動に利益を及ぼさなかった。しかしベラルーシ、イラン、ナイジェリアからの研究に基づくと、6ヵ月以上完全母乳哺育を継続した乳児では、消化管感染および呼吸器感染(イランおよびナイジェリアの研究)のリスクが有意に低減したと考えられた。フィンランド、オーストラリアおよびベラルーシの研究では、アトピー性湿疹、喘息、他のアトピー性アウトカムのリスク低減を認めなかった。ホンジュラスの2件の試験およびバングラデシュとセネガルからの観察研究のデータでは、6ヵ月までの完全母乳哺育により、月経再開が遅延し、ホンジュラスの試験では母体の分娩後体重減少が早かった。

著者の結論

6ヵ月間完全母乳哺育の乳児では、混合栄養の乳児に比べて3~4ヵ月時点で消化管感染による罹病率が低く、6ヵ月以上完全母乳哺育の発展途上国または先進国のいずれの乳児も成長の遅れを認めなかった。さらに、6ヵ月以上完全母乳哺育の乳児の母親の方が、授乳による無月経が延長した。不十分な発育や他の有害なアウトカムが見過ごされることなく十分な介入が行われるよう、乳児を個別に管理すべきであるが、入手したエビデンスによると、ローリソース国と先進国の両方において生後6ヵ月間の完全母乳哺育は、一般的方針として推奨しても明らかなリスクは認められなかった。

Abstrak

Tempoh optimum penyusuan eksklusif

Latar Belakang

Walaupun faedah penyusuan terhadap kesihatan telah diakui secara meluas, pendapat dan cadangan mengenai tempoh optimum penyusuan eksklusif masih diragui. Sejak tahun 2001, Pertubuhan Kesihatan Sedunia mengesyorkan penyusuan eksklusif selama enam bulan. Baru-baru ini, banyak perdebatan tertumpu pada keperluan mikronutrien, kewujudan dan kekuatan faedah kesihatan terhadap amalan tersebut di negara maju.

Matlamat

Untuk menilai kesan penyusuan eksklusif selama enam bulan berbanding penyusuan eksklusif untuk tiga hingga empat bulan diikuti dengan penyusuan campuran (pengenalan cecair pelengkap atau makanan pepejal beserta susu ibu) sehingga enam bulan terhadap kesihatan, pertumbuhan dan perkembangan kanak-kanak dan kesihatan ibu.

Kaedah Pencarian

Kami mencari dalam <I> Perpustakaan Cochrane </ I> (2011, Keluaran 6), MEDLINE (1 Januari 2007 hingga 14 Jun 2011), EMBASE (1 Januari 2007 hingga 14 Jun 2011), CINAHL (1 Januari 2007 hingga 14 Jun 2011 ), BIOSIS (1 Januari 2007 hingga 14 Jun 2011), Indeks Afrika Medicus (carian 15 Jun 2011), Indeks Medicus untuk WHO Timur Wilayah Mediterranean (IMEMR) (carian 15 Jun 2011), LILACS (Sains Kesihatan Amerika Latin dan Caribbean) (carian 15 Jun 2011). Kami juga menghubungi pakar-pakar dalam bidang ini.

Untuk ulasan sistematik versi pertama, carian pada tahun 2000 telah menghasilkan sejumlah 2668 petikan asli. Komunikasi dengan pakar-pakar dalam bidang ini telah menambah bilangan kajian yang diterbitkan dan tidak diterbitkan. Kemaskini kajian literatur pada Disember 2006 telah menghasilkan tambahan sebanyak 835 petikan asli.

Kriteria Pemilihan

Kami memilih semua kajian klinikal terkawal dan kajian pengamatan ke atas kesihatan kanak-kanak atau ibu yang membandingkan penyusuan eksklusif selama enam bulan atau lebih dengan penyusuan eksklusif sekurang-kurangnya tiga hingga empat bulan diikuti dengan penyusuan campuran sehingga sekurang-kurangnya enam bulan. Kajian dibahagikan mengikut reka bentuk kajian (kajian terkawal berbanding kajian pengamatan), asal (negara membangun berbanding negara maju) dan tempoh penyusuan (tiga hingga tujuh bulan berbanding seterusnya).

Pengumpulan Data dan Analisis

Kami menilai secara berasingan kualiti kajian dan data yang diekstrak.

Keputusan Utama

Kami telah mengenalpasti 23 kajian berbeza yang memenuhi kriteria pemilihan: 11 dari negara membangun (dua daripadanya adalah kajian terkawal di Honduras) dan 12 dari negara maju (semuanya kajian pengamatan). Definisi penyusuan eksklusif adalah berbeza-beza dalam setiap kajian. Kajian terkawal dan kajian pengamatan mendapati bahawa bayi yang diberi susu ibu sepenuhnya selama enam bulan tidak menunjukkan penurunan berat badan atau terbantutnya pertambahan panjang. Walau bagaimana pun, saiz sampel yang lebih besar diperlukan untuk menidakkan perbezaan kecil risiko kekurangan zat makanan. Di negara membangun, yang mana kandungan zat besi bagi bayi yang baru lahir mungkin suboptimal, penyusuan eksklusif selama enam bulan tanpa suplemen zat besi terbukti menjejaskan status kandungan darah. Berdasarkan kajian Belarus, penyusuan eksklusif selama enam bulan tidak memberi sebarang kesan (berbanding penyusuan eksklusif selama tiga bulan diikuti penyusuan campuran sehingga enam bulan) pada tinggi, berat, indeks jisim badan, karies gigi, kebolehan kognitif atau tingkah laku pada umur 6.5 tahun. Bagaimana pun, berdasarkan kajian di Belarus, Iran dan Nigeria, bayi yang menyusu eksklusif selama enam bulan atau lebih mempunyai risiko jangkitan usus perut dan (kajian di Iran dan Nigeria) jangkitan pernafasan yang lebih rendah. Tiada pengurangan ketara dalam risiko ekzema atopik, asma atau atopik lainnya dalam kajian di Finland, Australia dan Belarus. Data daripada dua kajian Honduras dan kajian pengamatan di Bangladesh dan Senegal mencadangkan bahawa penyusuan eksklusif selama enam bulan berkaitan dengan kelewatan datang haid manakala dalam kajian Honduras, berkaitan dengan penurunan berat badan ibu yang lebih cepat selepas bersalin.

Kesimpulan Pengarang

Bayi yang diberi susu ibu secara eksklusif selama enam bulan kurang mengalami jangkitan usus perut berbanding mereka yang diberi susu secara campuran selama tiga atau empat bulan dan tiada kerencatan pertumbuhan didapati bagi bayi yang menerima penyusuan eksklusif selama enam bulan atau lebih di negara membangun mahu pun negara maju. Tambahan pula, penyusuan menyebabkan ibu-ibu bayi tersebut lewat didatangi haid. Walau pun bayi masih perlu dirawat mengikut keperluan individu agar pertumbuhan atau kesan sampingan tidak terabai dan intevensi yang sewajarnya disediakan, bukti sedia ada menunjukkan tiada risiko yang jelas dalam mengesyorkan polisi penyusuan eksklusif selama enam bulan pertama di negara membangun dan negara maju.

Catatan terjemahan

Diterjemahkan oleh Norhayati Mohd Noor (Universiti Sains Malaysia). Untuk sebarang pertanyaan sila hubungi hayatikk@usm.my

Plain language summary

Optimal duration of exclusive breastfeeding

Exclusive breastfeeding for six months (versus three to four months, with continued mixed breastfeeding thereafter) reduces gastrointestinal infection and helps the mother lose weight and prevent pregnancy but has no long-term impact on allergic disease, growth, obesity, cognitive ability, or behaviour.

The results of two controlled trials and 21 other studies suggest that exclusive breastfeeding (no solids or liquids besides human milk, other than vitamins and medications) for six months has several advantages over exclusive breastfeeding for three to four months followed by mixed breastfeeding. These advantages include a lower risk of gastrointestinal infection, more rapid maternal weight loss after birth, and delayed return of menstrual periods. No reduced risks of other infections, allergic diseases, obesity, dental caries, or cognitive or behaviour problems have been demonstrated. A reduced level of iron has been observed in developing-country settings.

Résumé simplifié

Durée optimale de l'allaitement exclusif

L'allaitement exclusif pendant six mois (versus trois à quatre mois, avec la poursuite d'un allaitement mixte par la suite) réduit l'infection gastro-intestinale et aide la mère à perdre du poids tout en prévenant une nouvelle grossesse, mais n'a aucun impact à long terme sur les maladies allergiques, la croissance, l'obésité, la capacité cognitive ou le comportement.

Les résultats de deux essais contrôlés et de 21 autres études suggèrent qu'un allaitement exclusif (aucun solide ou liquide autre que le lait humain, hormis les vitamines et les médicaments) pendant six mois présente plusieurs avantages par rapport à un allaitement exclusif pendant trois à quatre mois suivi d'un allaitement mixte. Ces avantages comprennent un plus faible risque d'infection gastro-intestinale, une perte de poids plus rapide de la mère après l'accouchement et un retour tardif des règles. Il n'a été démontré aucune réduction des risques d'autres infections, de maladies allergiques, d'obésité, de caries dentaires ou de problèmes cognitifs ou comportementaux. Un taux de fer réduit a été observé dans les pays en développement.

Notes de traduction

Cette revue a été traitée par le groupe Cochrane sur la grossesse et la naissance, bien que son thème ne relève pas de la compétence de ce groupe. La compétence du groupe comprend le démarrage de l'allaitement, mais non le moment de son arrêt. Toutefois, le sujet revêt clairement une importance globale et du fait qu'il ne rentrait facilement dans le champ de compétence d'aucun Groupe thématique Cochrane, le groupe sur la grossesse et la naissance a été heureux d'aider à la publication. Cette revue était basée sur une revue systématique de M. Kramer commandée par l'Organisation mondiale de la Santé (OMS). La revue OMS a été évaluée de manière très approfondie par des experts en statistiques et méthodologie des revues, ainsi qu'en nutrition et allaitement des nourrissons, notamment des experts que le Groupe thématique aurait contactés pour nos propres besoins d'arbitrage scientifique. Nous n'avons donc pas recherché de protocole initial ni soumis la revue Cochrane à une autre évaluation de ce type. La revue a toutefois été évaluée par le panel de consommateurs du Groupe sur la grossesse et la naissance.

Cette revue présente d'autres caractéristiques inhabituelles :

  1. Son titre ne correspond pas au format Cochrane standard, mais nous n'avons pas été en mesure d'établir un titre adapté tout en rendant justice au champ d'application du sujet.

  2. Elle comporte des données issues d'études en plus des essais randomisés.

  3. L'auteur de contact aura seul la responsabilité de sa maintenance et de sa mise à jour, car la stratégie de recherche de notre Groupe thématique ne s'étend pas à ce sujet.

Jim Neilson
Coordinateur
Groupe Cochrane sur la grossesse et la naissance

Traduit par: French Cochrane Centre 13th September, 2012
Traduction financée par: Ministère du Travail, de l'Emploi et de la Santé Français

Laički sažetak

Optimalno trajanje isključivog dojenja

Isključivo dojenje tijekom 6 mjeseci (u usporedbi s isključivim dojenjem koje traje 3-4 mjeseca, s kombinacijom druge hrane i dojenja nakon toga) smanjuje probavne infekcije djece, pomaže majci da izgubi višak tjelesne težine i sprječava ponovnu trudnoću, ali nema dugoročni utjecaj na alergijske bolesti, rast, debljinu, kognitivne sposobnosti ili ponašanje.

Rezultati dvaju kontroliranih ispitivanja i 21 druge studije pokazuju da isključivo dojenje (bez ikakve druge krute ili tekuće hrane osim humanoga mlijeka, osim vitamina i lijekova) tijekom 6 mjeseci ima nekoliko prednosti u odnosu na isključivo dojenje koje traje 3 ili 4 mjeseca, nakon čega slijedi kombinacija dojenja i druge hrane. Ove prednosti uključuju niži rizik od probavnih infekcija u djece, brži gubitak viška tjelesne težine nakon porođaja i odgodu ponovne uspostave menstruacijskog ciklusa. Nije uočen smanjen rizik za druge infekcije, alergijske bolesti, debljinu, karijes, kognitivne probleme ili probleme u ponašanju. Smanjena razina željeza je uočena u djece u zemljama u razvoju.

Bilješke prijevoda

Prevoditelj:: Croatian Branch of the Italian Cochrane Centre

Resumo para leigos

Duração ideal do aleitamento materno exclusivo

A amamentação exclusiva por 6 meses (versus 3-4 meses, seguida de amamentação mista) reduz o risco de infecções gastrointestinais, ajuda na perda de peso da mãe e previne uma nova gravidez, porém não modifica o risco da criança ter doenças alérgicas no futuro, não afeta seu crescimento, seu risco de ter obesidade, sua habilidade cognitiva ou seu comportamento.

Os resultados de dois estudos controlados e de outros 21 estudos sugerem que o aleitamento materno exclusivo (sem outros alimentos ou líquidos além do leite materno, exceto por vitaminas ou medicamentos) por 6 meses traria vários benefícios a mais do que o aleitamento materno exclusivo por 3-4 meses seguido por amamentação mista. Estas vantagens incluem um menor risco de infecção gastrointestinal, uma perda de peso mais rápida para a mãe e maior tempo até ela voltar a ter menstruações. O aleitamento materno exclusivo não modifica os riscos do bebê ter outras infecções, doenças alérgicas, obesidade, cáries dentárias ou problemas cognitivos ou comportamentais. Em países em desenvolvimento, o aleitamento exclusivo pode levar a uma redução do nível de ferro dos bebês.

Notas de tradução

Traduzido por: Brazilian Cochrane Centre
Tradução patrocinada por: None

淺顯易懂的口語結論

完全純母乳餵食的最佳期間

純母乳餵食6個月 (與純母乳餵食3到4個月再混合母乳餵食比較),可減少腸胃道感染以及幫助母親減重及防止懷孕,對於過敏性疾病、生長、肥胖、認知能力與行為則無長期影響。

2個控制試驗與21個其他研究結果表示: 純母乳餵食6個月 (沒有混合固體或是液體,除了人類乳汁、維生素與藥物之外),與純母乳餵食3到4個月後再混合母乳餵食比較,具有許多好處。這些好處包括:腸胃道感染風險較低、產婦生產後減重快速,以及減緩經期回復的期間。也證明了沒有降低其他感染、過敏性疾病、肥胖、齲齒、或是認知能力、行為問題的風險。在發展中國家的組別,鐵質量較少已經被觀察到。

譯註

翻譯: East Asian Cochrane Alliance
翻譯補助: 台灣衛生福利部/台北醫學大學實證醫學研究中心

平易な要約

完全母乳哺育の至適期間

6ヵ月間の完全母乳哺育では(3~4ヵ月までの完全母乳哺育とその後の混合母乳栄養継続に比べて)消化管感染が減少し、母親の体重が減少し次の妊娠を予防するのに有用であり、アレルギー性疾患、成長、肥満、認知機能、行動への長期的影響はなかった。 2件の比較試験と21件の他の研究の結果から、6ヵ月間の完全母乳哺育(ビタミンおよび薬剤以外、人乳のほかの固形食や流動食なし)には、3~4ヵ月間の完全母乳哺育とその後の混合母乳栄養よりもいくつかの利点がある。これらの利点として、消化管感染リスクの低下、出産後の母体の体重減少の早さ、月経再開の遅延などが挙げられる。他の感染、アレルギー性疾患、肥満、う歯、認知または行動障害のリスクの低減は認められなかった。ローリソース国の状況では鉄の低下が観察された。

訳注

監  訳: 江藤 宏美,2012.12.27

実施組織: 厚生労働省委託事業によりMindsが実施した。

ご注意 : この日本語訳は、臨床医、疫学研究者などによる翻訳のチェックを受けて公開していますが、訳語の間違いなどお気づきの点がございましたら、Minds事務局までご連絡ください。Mindsでは最新版の日本語訳を掲載するよう努めておりますが、編集作業に伴うタイム・ラグが生じている場合もあります。ご利用に際しては、最新版(英語版)の内容をご確認ください。

Ringkasan bahasa mudah

Tempoh optimum penyusuan eksklusif

Penyusuan eksklusif selama enam bulan (berbanding tiga hingga empat bulan diikuti dengan penyusuan campuran) mengurangkan jangkitan usus perut dan membantu ibu menurunkan berat badan dan mencegah kehamilan tetapi tidak mempunyai kesan jangka panjang terhadap penyakit alahan, pertumbuhan, obesiti, kebolehan kognitif atau tingkah laku.

Keputusan daripada dua kajian terkawal dan 21 kajian lain menunjukkan bahawa penyusuan eksklusif (tiada pepejal atau cecair selain susu ibu, selain daripada vitamin dan ubat-ubatan) selama enam bulan mempunyai beberapa kelebihan berbanding penyusuan eksklusif untuk tiga hingga empat bulan diikuti dengan penyusuan campuran. Antara kelebihannya adalah risiko yang lebih rendah terhadap jangkitan usus perut, penurunan berat badan ibu yang lebih cepat selepas bersalin dan lewat didatangi haid. Pengurangan risiko terhadap jangkitan lain, penyakit alahan, obesiti, kerosakan gigi, masalah kognitif atau tingkah laku tidak dapat dibuktikan. Tahap kandungan zat besi yang lebih rendah telah dilihat di negara membangun.

Catatan terjemahan

Diterjemahkan oleh Norhayati Mohd Noor (Universiti Sains Malaysia). Untuk sebarang pertanyaan sila hubungi hayatikk@usm.my

Laienverständliche Zusammenfassung

Optimale Dauer des ausschließlichen Stillens

Eine ausschließliche Stillzeit von sechs Monaten (im Vergleich zu drei oder vier Monaten und anschließendem Zufüttern) verringert Magen-Darm-Infektionen und hilft der Mutter, Gewicht zu verlieren und nicht schwanger zu werden, hat aber keine langfristige Wirkung auf Allergien, Wachstum, Fettleibigkeit, kognitive Fähigkeiten oder das Verhalten.

Die Ergebnisse von zwei kontrollierten und 21 weiteren Studien legen nahe, dass eine ausschließliche Stillzeit von sechs Monaten (d.h. ohne fester oder flüssiger Nahrung zusätzlich zur Muttermilch, jedoch Vitaminen und Medikamenten) mehrere Vorteile gegenüber einer ausschließlichen Stillzeit von drei oder vier Monaten und anschließendem Zufüttern hat. Zu diesen Vorteilen gehören ein geringeres Risiko für Magen-Darm-Infektionen, eine schnellere Gewichtsabnahme bei der Mutter nach der Geburt und ein späteres Wiedereinsetzen der Menstruation. Ein geringeres Risiko für andere Infektionen, Allergien, Fettleibigkeit, Karies oder kognitive bzw. Verhaltensprobleme wurde nicht nachgewiesen. In Entwicklungsländern wurde ein verminderter Bluteisenspiegel beobachtet.

Anmerkungen zur Übersetzung

Freigegeben durch Cochrane Schweiz

எளியமொழிச் சுருக்கம்

பிரத்தியேக தாய்ப் பாலுட்டலுக்கான உகந்த கால வரையறை

ஆறு மாத பிரத்தியேக தாய்ப் பாலுட்டல் (மூன்று முதல் நான்கு மாதங்களுக்கு, மற்றும் அதன்பின் தொடரப்படும் கலவையான தாய் பாலுட்டலுக்கு எதிராக) இரையக-குடலிய தொற்றை குறைக்கும் மற்றும் தாய் உடல் எடை குறைய உதவும் மற்றும் கர்ப்பத்தை தடுக்கும், ஆனால்,ஒவ்வாமை நோய், வளர்ச்சி, உடற் பருமன், புலனுணர்வு திறன் அல்லது நடத்தை மீது எந்த நீண்ட -கால தாக்கமும் இல்லை.

கலவையான தாய்ப் பாலுட்டலால் பின் தொடரப்பட்ட மூன்று முதல் நான்கு மாத பிரத்தியேக தாய்ப் பாலுட்டலை விட, ஆறு மாத பிரத்தியேக தாய்ப் பாலுட்டல் (, வைட்டமின்கள் மற்றும் மருந்துகள் தவிர தாய்ப்பாலை தாண்டி எந்த திட அல்லது திரவ உணவும் இல்லை) அநேக அனுகூலங்களை கொண்டுள்ளது என்று இரண்டு கட்டுப்பாட்டு சோதனைகள் மற்றும் பிற 21 ஆய்வுகளின் முடிவுகள் பரிந்துரைக்கின்றன. இரையக-குடலிய தொற்று அபாய குறைவு, குழந்தை பேற்றிற்கு பின் அதிக விரைவான தாய் உடல் எடை குறைவு, மற்றும் தாமதமாக திரும்பும் மாதவிடாய் சுழற்சிகள் ஆகியவை இந்த அனுகூலங்களில் அடங்கும். பிற தொற்றுகள், ஒவ்வாமை நோய்கள், உடற் பருமன், பல் சொத்தை அலல்து புலனுணர்வு அல்லது நடத்தை பிரச்சனைகள் மீதான எந்த அபாய குறைவுகளும் விளக்கப்படவில்லை. முன்னேறும்-நாடு அமைப்புகளில், இரும்புச் சத்து அளவு குறைதல் கண்டறியப்பட்டுள்ளது.

மொழிபெயர்ப்பு குறிப்புகள்

மொழிபெயர்ப்பாளர்கள்: சிந்தியா ஸ்வர்ணலதா ஸ்ரீகேசவன், ப்ளசிங்டா விஜய், தங்கமணி ராமலிங்கம், ஸ்ரீகேசவன் சபாபதி.

Background

Although the health benefits of breastfeeding are widely acknowledged, opinions and recommendations are strongly divided on the optimal duration of exclusive breastfeeding (Fewtrell 2011). The epidemiologic evidence is now overwhelming that, even in developed countries, breastfeeding protects against gastrointestinal and (to a lesser extent) respiratory infection, and that the protective effect is enhanced with greater duration and exclusivity of breastfeeding (Ip 2007). ('Greater duration and exclusivity' is used in a general sense here; the references cited do not pertain specifically to the subject of this review, i.e., the optimal duration of exclusive breastfeeding.) Prolonged and exclusive breastfeeding has also been associated with a reduced risk of the sudden infant death syndrome and, in preterm infants, necrotizing enterocolitis (Ip 2007). Breastfeeding is life-saving in developing countries; a meta-analysis (WHO 2001a) reported markedly reduced mortality (especially due to infectious disease) with breastfeeding even into the second year of life.

Although growth faltering is uncommon in developed countries, a pooled analysis of U.S., Canadian, and European data sets undertaken by the WHO Working Group on Infant Growth (Dewey 1995) showed that infants from developed countries who followed then current WHO feeding recommendations (to exclusively breastfeed for four to six months of age and to continue breastfeeding with adequate complementary foods up to two years of age) show a deceleration in both weight and length gain relative to the then existing international WHO/CDC growth reference from around three to 12 months, with partial catch-up in the second year. The Euro-Growth study (Haschke 2000) also reported an association between prolonged and exclusive breastfeeding and slower growth during infancy. In developed-country settings, it is not at all clear that the more rapid growth reported in infants who are formula-fed, or breastfed less exclusively and for a shorter duration, is an advantage. Moreover, a large, cluster-randomized trial from Belarus has reported that breastfed infants born and followed at sites randomized to a breastfeeding promotion intervention (and who were breastfed more exclusively and for a longer duration) actually grew more rapidly in the first six to nine months than those born and followed at control (nonintervention) sites (Kramer 2000a). Based on this evidence, WHO has developed new growth standards for infancy and early childhood (De Onis 2006a; De Onis 2006b).

The evidence bearing on longer-term outcomes is more controversial. For allergic (atopic) diseases, meta-analyses support a protective effect against atopic dermatitis (eczema), at least in infancy (Gdalevich 2001a; Ip 2007). For asthma, one earlier meta-analysis (Gdalevich 2001b) also suggested a protective effect, although a recently updated meta-analysis (Ip 2007) that excludes a suspected fraudulent study by Chandra and Hamed (Chandra 1991) suggests no significant effect. The intention-to-treat analysis of the Belarusian trial of a breastfeeding promotion intervention also reported no reduction of asthma risk (Kramer 2000a). The evidence of long-term effects of breastfeeding on obesity and mean body mass index (Kramer 2000a; Owen 2005a; Owen 2005b) or blood pressure, type 1 or type 2 diabetes, or ischemic heart disease (Ip 2007) is also weak. Meta-analyses (Anderson 1999; Ip 2007) have reached opposite conclusions about breastfeeding effects on neurocognitive ability. The intention-to-treat analysis of the Belarusian breastfeeding promotion trial reported significant effects on verbal IQ and teachers' ratings of writing and reading performance in school (Kramer 2000a). Evidence also suggests that prolonged (more than six months) breastfeeding provides protection against both acute lymphoblastic and myeloblastic leukemia in childhood (Ip 2007). Long-term maternal health benefits have also received considerable attention in developed countries, with Ipp et al concluding protection against breast cancer and ovarian cancer and possible reduction in the risk of type 2 diabetes (Ip 2007). Importantly, most of the evidence bearing on these long-term health outcomes is based on comparisons of any breastfeeding, or of an arbitrary "minimum" duration and/or degree of breastfeeding, with no breastfeeding (i.e., formula feeding).

Most of the scientific evidence on the health effects of breastfeeding has been based on observational studies, with well-recognized sources of potential bias. Some of the biases tend to favour exclusively breastfed infants, while others favour those who receive earlier complementary feeding. Reverse causality is an important potential source of bias. Infants who continue to be exclusively breastfed tend to be those who remain healthy and on an acceptable growth trajectory; significant illness or growth faltering can lead to interruption of breastfeeding or supplementation with infant formula or solid foods (Hill 1977; Sauls 1979). Infants who develop a clinically important infection are likely to become anorectic (loss of appetite) and to reduce their breast milk intake, which can in turn lead to reduction in milk production and even weaning (Bauchner 1986). The temporal sequence of the early signs of infection and weaning may not be adequately appreciated; infection may be blamed on the weaning, rather than the reverse. Advanced neuromotor development may also lead to earlier induction of solid foods, which could then receive 'credit' for accelerating motor development (Heinig 1993). Poorly-growing infants (especially those in developing countries) are likely to receive complementary feedings earlier because of their slower growth. In developed countries, however, rapidly-growing infants may require more energy than can be met by the increasingly spaced feedings typical of such settings. This may result in crying and poor sleeping, supplementation with formula or solid foods, or both, reduced suckling, and a vicious cycle leading to earlier weaning (i.e., discontinuation of breastfeeding) (Kramer 2000a). In addition, unmeasured, poorly measured, or uncontrolled confounding variables are also likely to bias the association between introduction of complementary foods and infant health outcomes.

Finally, the underlying assumption in this field has been that 'one size fits all', i.e., that average population effects can be applied to individual infants and that one international recommendation is therefore adequate for all infants. There has been little discussion of the fact that all infants, regardless of how they are fed, require careful monitoring of growth and illness, with appropriate interventions undertaken whenever clinically indicated.

Objectives

The primary objective of this review was to assess the effects on child health, growth, and development, and on maternal health, of exclusive breastfeeding for six months versus exclusive breastfeeding for three to four months with mixed breastfeeding (introduction of complementary liquid or solid foods with continued breastfeeding) thereafter through six months. A secondary objective was to assess the child and maternal health effects of prolonged (more than six months) exclusive breastfeeding versus exclusive breastfeeding through six months and mixed breastfeeding thereafter.

Methods

Criteria for considering studies for this review

Types of studies

We selected controlled clinical trials and observational studies, published in all languages, examining whether or not exclusive breastfeeding (EBF) until six months of age has an impact on growth, development, morbidity, and survival of healthy, term infants and their mothers. Studies of (or including) low birthweight (less than 2500 g) infants were not excluded, provided that such infants were born at term (at least 37 completed weeks). Only those studies with an internal comparison group were included in the review, i.e., we excluded studies based on external comparisons (with reference data). The comparisons must have been based on one group of infants who received EBF for at least three but less than seven months and mixed breastfeeding (MBF) until six months or later (i.e., infants were introduced to liquid or solid foods between three and six months of age), and another group of infants who were exclusively breastfed for at least six months. This restriction was imposed to provide direct relevance to the clinical and public health decision context: whether infants who are exclusively breastfed for the first three to four months should continue EBF or should receive complementary foods in addition to breast milk (MBF). Thus studies comparing EBF and MBF from birth were excluded, as were those that investigated the effects of age at introduction of nonbreast milk liquid or solid foods but did not ensure EBF at least three months prior to their introduction. We also included studies comparing infants receiving prolonged EBF (more than six months) to those exclusively breastfed for six months and continued MBF after six months.

Types of participants

Lactating mothers and their healthy, term, singleton infants.

Types of interventions

Among infants EBF for at least three months, the interventions/exposures compared were continued EBF versus MBF. The 'complementary' foods used in MBF included juices, formula, other milks, other liquids, or solid foods. Although the World Health Organization (WHO) defines EBF as breastfeeding with no supplemental liquids or solid foods other than medications or vitamins, few studies strictly adhered to the WHO's definition. In some studies, so-called 'EBF' included provision of water, teas, or juices (corresponding to WHO's definition of predominant breastfeeding) (WHO 1991) or even small amounts of infant formula. The definitions of EBF and MBF used in each study are described in the Characteristics of included studies table.

Types of outcome measures

No infant or maternal health outcomes were excluded from consideration. The infant outcomes specifically sought (but not necessarily found) included growth (weight, length, and head circumference and z-scores (based on the WHO/CDC reference) for weight-for-age, length-for-age, and weight-for-length), infections, morbidity, mortality, micronutrient status, neuromotor and cognitive development, asthma, atopic eczema, other allergic diseases, type 1 diabetes, blood pressure, and subsequent adult chronic diseases such as coronary heart disease, hypertension, type 2 diabetes, and inflammatory and autoimmune diseases. Maternal outcomes sought included postpartum weight loss, duration of lactational amenorrhea, and such chronic diseases as breast and ovarian cancer and osteoporosis.

Search methods for identification of studies

Electronic searches

See Appendix 1 for details of searches carried out in previous versions of the review. The 2011 updated literature review included the same electronic databases as the 2007 update except for CAB Abstracts and HealthSTAR.

  • The Cochrane LIbrary (2011, Issue 6)

  • MEDLINE (1 January to 14 June 2011)

  • EMBASE (1 January 2011 to 14 June 2011)

  • CINAHL (1 January 2007 to 14 June 2011)

  • BIOSIS (1 January 2007 to 14 June 2011)

  • African Index Medicus (searched 15 June 2011)

  • Index Medicus for the WHO Eastern Mediterranean Region (IMEMR) (searched 15 June 2011)

  • LILACS (searched 15 June 2011

Searching other resources

In addition to the studies found through these electronic searches, we checked reference lists of identified articles, and contacted experts in the field to identify other potentially relevant published or unpublished studies. We attempted to contact the authors of all studies that qualified for inclusion in the review to obtain methodologic details, clarify inconsistencies, and obtain unpublished data.

For all searches, every effort was made to identify relevant non-English language articles and abstracts. Given their own backgrounds, the review authors themselves were able to determine the eligibility of articles in French, Spanish, and Japanese. For publications in other languages, two options were available. Many articles in languages other than English provided English abstracts. As such, all potentially relevant articles were obtained and checked for availability of English abstracts. If such abstracts were not available, or were available but did not provide enough information to determine their eligibility, then assistance was requested from WHO to determine their eligibility for inclusion. No article or abstract was excluded because of language of publication.

Data collection and analysis

We evaluated studies under consideration for methodological quality and appropriateness for inclusion without consideration of their results. The criteria for quality assessment were developed a priori and are presented below.

We used Cochrane criteria for assessing controlled clinical trials. As shown below, this method rates trials on three elements.

1) Adequacy of randomization and concealment:
A. randomized and concealed appropriately;
B. randomized appropriately but concealment unclear from the description;
C. not (or not reported as) randomized or inadequate concealment, or both.

2) Losses to follow-up and analysis:
A. used intention-to-treat (ITT) analysis, with losses to follow-up symmetrical and less than 15% in each group;
B. symmetrical losses were at least 15%, but analysis was based on ITT;
C. asymmetrical losses to follow-up despite use of ITT, or analysis not based on ITT.

3) Measurement of outcome (outcome-specific):
A. blinding of observers or 'objective' outcomes (e.g., measured weight);
B. nonblinding of observers for measurements that could be affected by bias (including length, head circumference, and self-reported outcomes).

The five-point Jadad (Jadad 1996) scale was also used to examine the quality of randomized controlled trials. Details of the scale are as follows.

1) Was the study described as randomized (this includes the use of words such as randomly, random, and randomization)?
a) not random or not mentioned (0);
b) random, described, and inappropriate (0);
c) random, not described (+1);
d) random, described, and appropriate (+2).

2) Was the study described as double-blind?
a) not double-blind (0);
b) double-blind, described, and not appropriate (0);
c) double-blind, not described (+1);
d) double-blind, described, and appropriate (+2).

3) Was there a description of withdrawals and dropouts?
Withdrawals (number and reasons) must be described by group to get 1 point.

Observational (cohort, case-control, and cross-sectional studies) were assessed for control for confounding, losses to follow-up, and assessment of outcome as follows.

1) For growth and morbidity outcomes, control for confounding by socioeconomic status, water supply, sanitation facilities, parental height and weight, birthweight, and weight and length at three months (or age at which complementary feeding was introduced in the mixed breastfeeding group):
A. control for all (or almost all) pertinent confounders;
B. partial control for some confounders;
C. no control for confounding.

2) Losses to follow-up:
A. losses to follow-up were symmetrical and less than 15% in each group;
B. losses were 15% to 25% and symmetrical;
C. losses were greater than 25%, asymmetrical, or not reported (and all cross-sectional studies).

3) Assessment of outcome (outcome-specific):
A. blinding of observers or 'objective' outcomes (e.g., measured weight);
B. nonblinding of observers or measurements that could be affected by bias (including length, head circumference, and self-reported outcomes).

Quality assessments of all eligible studies were carried out independently by the two review authors. Disagreements were resolved by consensus. Data were extracted independently by both review authors, with disagreements resolved by consensus. Attempts were made to contact authors of included studies to obtain additional data, resolve inconsistencies, and obtain additional methodologic details.

The studies were stratified according to study design (controlled trials versus observational studies), provenance (developing versus developed countries), and timing of feeding comparison (three to seven months versus 'prolonged' (more than six months)). (One study (WHO 1997) based on a pooled analysis of two developed and three developing countries has been included with developed-country studies because of the selection criteria (literate, educated, urban mothers) and the observed high infant growth rates.) This resulted in five separate strata for considering the results of the studies located by the literature search: (1) controlled trials of exclusive versus mixed breastfeeding for four to six months from developing countries; (2) observational studies of exclusive versus mixed breastfeeding for three to seven months from developing countries; (3) observational studies of prolonged (more than six months) exclusive versus mixed breastfeeding from developing countries; (4) observational studies of exclusive versus mixed breastfeeding for three to seven months from developed countries; and (5) observational studies of prolonged (more than six months) exclusive versus mixed breastfeeding from developed countries. In accordance with conventional terminology used in Cochrane reviews, these strata are labelled below as 'comparisons'. Outcomes for each comparison are presented sequentially.

Inter-study heterogeneity was evaluated for all outcomes and all comparisons using the I² statistic. Fixed-effect measures of association are reported for all analyses except for those for which the I² exceeded 50%; the latter analyses are based on random-effect measures. For observational studies that used multivariable regression models to control for potentially confounding covariates, association measures and their 95% confidence intervals are provided in the text of the review but do not appear in the data tables or graphs.

Results

Description of studies

See: Characteristics of included studies; Characteristics of excluded studies.

For details of included and excluded studies, see the Characteristics of included studies and Characteristics of excluded studies tables.

Results of the search

The June 2011 search yielded 3425 additional unique citations and from these we included one additional study (Duijts 2010) plus a later follow-up from Kramer 2000a. The selected studies are listed in the Characteristics of included studies table. (For details of search results from previous searches, see Appendix 1.)

Risk of bias in included studies

See Characteristics of included studies table.

Effects of interventions

Comparison one: controlled trials of exclusive versus mixed breastfeeding for four to six months, developing countries

Two studies were found in this category, both from the same group of investigators and involving the same study setting (Honduras). The first of these studies, Cohen 1994a, involved term infants unselected for birthweight but included 29 infants (19.9%) weighing less than 2500 g at birth. The second, Dewey 1999a, was restricted to term infants weighing less than 2500 g at birth. The quality ratings of these two trials were not high for several reasons. First, in both trials, allocation was within clusters defined by weeks, rather than to individual women, yet the results were analyzed with individual women and infants as the units of analysis; any similarities in outcome within weeks (intracluster correlation) would tend to reduce the true effective sample size and thereby overestimate the precision (i.e., underestimate the variance) of the results. Second, the first trial allocated the weeks by alternation, rather than by strict randomization, thereby creating a potential for nonconcealment and uncontrolled confounding bias at enrollment (although there is no evidence that such bias actually occurred). Third, the published results were not based on analysis by intention-to-treat. Most of the babies not analyzed in these two trials were truly lost to follow-up; however, rather than excluded for noncompliance, the latter were restricted to four babies (three in the exclusive breastfeeding (EBF) group, one in the mixed breastfeeding (MBF) group) in the first trial and three babies (all three in the exclusive breastfeeding group) in the second trial. Moreover, the investigators have provided (unpublished) data on weight and length gain on five of the nine dropouts in the second Honduran trial (three of the nine moved away before six months), thereby substantially reducing the potential for selection bias in the analysis of that trial.

Most importantly, despite the above-noted methodological problems, these two trials are the only studies uncovered by our search that used an experimental design to specifically address the four to six months versus 'about six months' debate. Thus, at least with respect to bias due to known and unknown confounding variables, these trials are methodologically superior to any of the observational studies included in this review despite their methodological imperfections. Furthermore, the investigators made a considerable effort to ensure compliance with the assigned allocation and to standardize the training of the observers who performed the anthropometric measurements, thereby reducing the random error (improving the precision) of these measurements. Finally, detailed comparisons between trial participants and eligible nonparticipants demonstrated no differences that would detract from the external validity (generalizability) of the trials' findings, at least for the specific type of setting where the study was conducted (an urban, low-income population in Honduras).

For all analyses, the two mixed breastfeeding groups (one of which was intended to maintain frequency of breastfeeding) in the first trial were combined for the purposes of this analysis. Monthly weight gain from four to six months was nonsignificantly slightly higher among infants whose mothers were assigned to continued exclusive breastfeeding (mean difference (MD) +20.78; 95% confidence interval (CI) -21.99 to +63.54 g/mo) (Analysis 1.1). Thus the 95% CI is statistically compatible with a weight gain only 22 g/mo lower in the EBF group, which represents approximately 5% of the mean and 15% of the standard deviation (SD) for the monthly weight gain. Weight gain from six to 12 months was almost identical in the two groups (MD -2.62; 95% CI -25.85 to 20.62 g/mo) (Analysis 1.2).

For length gain from four to six months, the MD was 1.0 mm/mo (95% CI -0.40 to +2.40 mm/mo) (Analysis 1.3); the lower confidence limit represents only 2% of the mean and 8% of the SD for monthly length gain. As with weight gain, length gain from 6 to 12 months was nearly identical in the two groups (MD -0.04; 95% CI -0.10 to 0.02 cm/mo) (Analysis 1.4).

Weight-for-age, length-for-age, and weight-for-length z-scores at six months were all nonsignificantly higher in the EBF group (MD +0.18; 95% CI -0.06 to +0.41 (Analysis 1.5); MD +0.11; 95% CI -0.11 to +0.33 (Analysis 1.6); and MD +0.09; 95% CI -0.13 to +0.31 (Analysis 1.7), respectively).

The impact of the small sample size of the two Honduran trials is evident when examining the risk of undernutrition, as represented by anthropometric z-scores less than -2 at six months. For weight-for-age, the pooled risk ratio (RR) was 2.14 (95% CI 0.74 to 6.24) (Analysis 1.8), which is statistically compatible with a six-fold increase in risk. The results were somewhat more reassuring for length-for-age (RR 1.18; 95% CI 0.56 to 2.50) (Analysis 1.9) but not for weight-for-length (RR 1.38; 95% CI 0.17 to 10.98) (Analysis 1.10).

All hematologic results (Analysis 1.11 to Analysis 1.19) are based on the first Honduras trial (Cohen 1994a), since in the second trial (Dewey 1999a, restricted to low birthweight infants), infants with low hemoglobin concentrations at two and four months were supplemented with iron. A nonsignificantly higher proportion of infants in the exclusively breastfed group received iron supplements from six to nine months (RR 1.20; 95% CI 0.91 to 1.58) (Analysis 1.11). This is consistent with the significantly lower average hemoglobin concentration at six months in the exclusively breastfed group (difference = -5.00 (95% CI -8.46 to -1.54) g/L) (Analysis 1.12). A nonsignificantly higher proportion of exclusively breastfed infants had a hemoglobin concentration below 110 g/L at six months (RR 1.20; 95% CI 0.91 to 1.58) (Analysis 1.13). Similarly, mean plasma ferritin concentration was significantly lower at six months in the exclusively breastfed infants (difference = -18.90 (95% CI -37.31 to -0.49) mcg/L) (Analysis 1.17), with a RR for a low (less than 15 mcg/L) ferritin concentration of 2.93 (95% CI 1.13 to 7.56) (Analysis 1.19).

In the second trial, no significant effect was seen on the proportion of infants with a low zinc concentration (less than 70 mcg/dL) at six months (RR 0.75; 95% CI 0.43 to 1.33) (Analysis 1.20).

In the pooled results from both Honduran trials, no significant difference was seen between the EBF and MBF groups for the percentage of days with fever (Analysis 1.21), cough (Analysis 1.22), or nasal congestion (Analysis 1.23), nasal discharge (Analysis 1.24), hoarseness (Analysis 1.25), or diarrhea (Analysis 1.26) from four to six months, nor for fever (Analysis 1.27), nasal congestion (Analysis 1.28), or diarrhea from six to 12 months (Analysis 1.29).

Again based on pooled results from both trials, mothers in the exclusively breastfed group reported that their infants crawled at an average of -0.80 (95% CI -1.26 to -0.34) months sooner (Analysis 1.30). No difference was seen, however, in the mean age at which the infants were reported to have first sat from a lying position (average MD -0.22 (95% CI -0.91 to 0.46) months), random-effects (Analysis 1.31). The results from the two Honduras trials (Cohen 1994a; Dewey 1999a) differed with respect to maternal reports of walking by 12 months (Analysis 1.32), with a significantly lower proportion of exclusively breastfed infants reported as not having walked by 12 months in the first trial (RR 0.66; 95% CI 0.45 to 0.98) (Cohen 1994a), but a nonsignificantly higher proportion not having done so in the second trial (RR 1.12; 95% CI 0.90 to 1.38) (Dewey 1999a), with statistically significant (P < .01) heterogeneity between the two trials.

Mothers in the exclusively breastfed group (from the two trials combined) had a statistically significantly larger weight loss from four to six months (MD 0.42; 95% CI 0.02 to 0.82) kg) (Analysis 1.33). Women in the exclusively breastfed group were also nonsignificantly less likely to have resumed menses by six months postpartum (RR 0.58; 95% CI 0.33 to 1.03); the effect was statistically significant in the second Honduras trial when considered alone (RR 0.35; 95% CI 0.14 to 0.91) (Dewey 1999a) (Analysis 1.34).

Comparison two: observational studies of exclusive versus mixed breastfeeding for three to seven months, developing countries

The main concern in using an observational design to compare outcomes with EBF versus MBF is confounding due to differences in socioeconomic status, water and sanitation facilities, parental size (a proxy for genetic potential), and (perhaps most importantly) weight and length at the time complementary foods were first introduced in the mixed breastfeeding group. The latter source of confounding (i.e., by indication) will arise if poorly-growing infants are more likely to receive complementary foods.

Four cohort studies in this category from Peru (Brown 1991a), the Philippines (Adair 1993a), Senegal (Simondon 1997a), and Iran (Khadivzadeh 2004) found no evidence of confounding by indication, Adair 1993a found no confounding by several other potential factors, and (in unpublished data provided by the authors). Simondon 1997a calculated adjusted means for weight and length gain from four to six months. Nonetheless, the inability of observational studies to control for subtle (and unknown) sources of confounding and selection bias suggests the need for cautious interpretation. All four studies reported on monthly weight gain from four to six months (Analysis 2.1). The MD was -10.10 (95% CI -27.68 to +7.48) g/mo, a lower confidence limit compatible with a deficit of only 7% of the mean and less than 15% of the SD for monthly weight gain. The Simondon 1997a study also reported on monthly weight gain from six to nine months (difference = -6.00 (95% CI -54.15 to +42.15) g/mo) (Analysis 2.2). All four studies also reported on monthly length gain from four to six months (Analysis 2.3); the MD was 0.04 (95% CI -0.02 to 0.11) cm/mo, a lower confidence limit statistically compatible with a reduced length gain in the EBF group less than 2% of the mean and 4% of the SD. The Simondon 1997a study also reported on monthly length gain from six to nine months (Analysis 2.4), and again the results excluded all but a small reduction in the exclusively breastfed group (difference = 0.04 (95% CI -0.06 to 0.14) cm/mo).

Onayade 2004 actually reported significantly higher absolute weights at both five and six months in the EBF group but did not analyze weight gains; the absence of control for confounding differences between the EBF and MBF groups, as well as the possibility of reverse causality (i.e., those infants with lower weights may have been more likely to receive complementary feeding) argue for cautious interpretation, however.

The Simondon 1997a study also provided (unpublished) data on anthropometric z-scores and mid-upper arm circumference. EBF was associated with nonsignificantly higher MD z-scores at six to seven and nine to 10 months: +0.13 (95% CI -0.09 to +0.35) (Analysis 2.5) and +0.09 (95% CI -0.15 to +0.33) (Analysis 2.6), respectively, for weight-for-age; +0.04 (95% CI -0.14 to +0.22) (Analysis 2.7) and +0.11 (95% CI -0.09 to +0.31) (Analysis 2.8), respectively, for length-for-age; and +0.11 (95% CI -0.09 to +0.31) (Analysis 2.9) and +0.01 (95% CI -0.21 to +0.23) (Analysis 2.10), respectively, for weight-for-length. The risk ratio for low (less than -2) z-scores at six to seven and nine to 10 months were 0.92 (95% CI 0.54 to 1.58) (Analysis 2.11) and 0.93 (95% CI 0.64 to 1.36) (Analysis 2.12), respectively, for weight-for-age; 1.20 (95% CI 0.57 to 2.53) (Analysis 2.13) and 1.21 (95% CI 0.62 to 2.37) (Analysis 2.14), respectively, for length-for-age; and 0.42 (95% CI 0.12 to 1.50) (Analysis 2.15) and 0.82 (95% CI 0.39 to 1.71) (Analysis 2.16), respectively, for weight-for-length. Mid-upper arm circumference was nonsignificantly higher in the EBF group at both six to seven and nine to 10 months: MD 0.20 (95% CI -0.04 to 0.44) cm (Analysis 2.17) and 0.10 (95% CI 0.16 to 0.36) cm (Analysis 2.18), respectively.

Khadivzadeh 2004 found a lower incidence of both gastrointestinal (11 versus 27%; RR 0.41; 95% CI 0.21 to 0.78) (Analysis 2.19) and respiratory (23 versus 35%; RR 0.68; 95% CI 0.43 to 1.06) Analysis 2.20) infection at four to six months in the EBF group. Onayade 2004 reported corresponding crude ORs of 0.02 (95% CI 0.01 to 0.09) and 0.43 (95% CI 0.17 to 1.00), respectively, but did not provide numerators and denominators and did not control for confounding differences between the EBF and MBF groups.

Huffman 1987 reported a longer median duration of lactational amenorrhea associated with EBF (for at least seven months) versus MBF (16.1 versus 15.3 months, respectively), but means and SDs were not reported. In a multivariate (Cox) regression model adjusting for maternal education, parity, religion, and weight, EBF for at least six months was associated with a significantly longer time to resumption of menses versus EBF for less than one month, but no direct comparison was reported versus MBF. Simondon 1997a reported a lower risk of resumption of menses by six to seven months (Analysis 2.21) in the EBF group: crude RR 0.19 (95% CI 0.05 to 0.79), adjusted odds ratio (OR) 0.19 (95% CI 0.04 to 0.86).

Cross-sectional studies share all of the methodological shortcomings of other observational designs (see above) plus one important additional one: selective loss to follow-up. In particular, children who die, are hospitalized, or are referred to a site other than the one under study, may be more likely to experience morbidity or suboptimal growth. If such (unstudied) infants are more heavily represented in one of the feeding groups, the resulting comparison will be biased.

One large cross-sectional study from Chile (Castillo 1996) reported a similar risk of weight-for-age z-score less than -1 and height-for-age z-score less than -1 from three to five and six to eight months in the two feeding groups, but the prevalences, CIs, and standard errors for the reported prevalence ratios are not published, thus precluding any assessment of sampling variation.

Comparison three: observational studies of prolonged (more than six months) exclusive versus mixed breastfeeding, developing countries

One small cross-sectional study from Pune, India (Rao 1992) permitted analysis only of male infants, since a relatively large fraction of female infants in the MBF group received artificial feeding in the first six months of life. The results (Analysis 3.1) showed a nonsignificant reduction of low (less than 75% of the reference mean) weight-for-age at six to 12 months of age in the exclusively breastfed males (RR 0.61; 95% CI 0.26 to 1.43). The strong possibility of confounding by age, even within the range of six to 12 months (the EBF group is likely to have been younger, on average, and therefore less undernourished), further limits the reported result.

A cohort study from Bangladesh (Khan 1984) reported similar weight and length gains in infants who were exclusively breastfed, those who were breastfed with supplements beginning at six to 11 months, and those who were exclusively breastfed for 12 months and supplemented between 12 and 15 months. Unfortunately, the data are presented only graphically and without standard deviations, thus preventing a quantitative assessment or pooling with data from other studies.

Comparison four: observational studies of exclusive versus mixed breastfeeding for three to seven months, developed countries

A pooled sample of breastfed infants from seven studies carried out in six developed countries (WHO 1994a), a pooled analysis from five countries (two developed, three developing, but in which study women were all literate and of middle to high socioeconomic status) (WHO 1997), a large cohort study nested within a randomized trial in Belarus (Kramer 2000a), and a small study from Sweden (Akeson 1996a) reported on weight gain between three and eight months. WHO 1997 and Kramer 2000a controlled for confounding by indication (size or growth in first three to four months) and other potential confounders using multilevel (mixed) regression analyses. Substantial (I2 = 69%) heterogeneity was observed among the four studies, with considerably larger mean weight gains in both groups from Belarus and a slightly but significantly higher gain in the MBF group (Analysis 4.1). The pooled random-effects MD is -7.95 [-31.84, 15.93] g/mo. Heinig 1993 and Kramer 2000a also reported on weight gain between six and nine months (Analysis 4.2). Again, the results show significant heterogeneity (I2 = 76%) but are dominated by the larger size of the Belarussian study. The pooled random-effects MD is 21.11 [-44.70, 86.91] g/mo. Akeson 1996a, Heinig 1993, and Kramer 2000a reported on weight gain from eight to 12 months (Analysis 4.3); the MD was -1.82 (95% CI -16.72 to +13.08) g/mo, which excludes a reduced length gain in the EBF group of 5% of the mean and 10% of the SD for the Belarusian study.

For length gain at three to eight months (Analysis 4.4), the studies again show significant (I2 = 76%) heterogeneity. Kramer 2000a found a slightly but significantly lower length gain in the EBF group at four to eight months (-0.11 [-0.17, 0.05] mm/mo), whereas the pooled analysis yielded a random-effects average MD of -0.03 [-0.11, 0.06] mm/mo. Heinig 1993 and Kramer 2000a also reported on length gain at six to nine months (MD -0.04; 95% CI -0.10 to 0.01) cm/mo) (Analysis 4.5). For the eight to 12 month period, the results show a slightly but significantly higher length gain in the EBF group (MD +0.09; 95% CI 0.03 to +0.14) cm/mo (Analysis 4.6).

Observational analyses from the Belarusian study (Kramer 2000a) also include data on weight-for-age, length-for-age, and weight-for-length z-scores at six, nine, and 12 months. Means in both the EBF and MBF groups were well above (+0.5 to +0.6) the reference values at all three ages. Nonetheless, the weight-for-age z-score was slightly but significantly lower in the EBF group at all three ages: MD -0.09 (95% CI -0.16 to -0.02) (Analysis 4.7) at six months, -0.10 (95% CI -0.18 to -0.02) (Analysis 4.8) at nine months, and -0.09 (95% CI -0.17 to -0.01) (Analysis 4.9) at 12 months. Length-for-age z-scores were very close to the reference (0) at six and nine months and slightly above the reference (0.15) at 12 months. Again, the EBF group had slightly but significantly (except at 12 months) lower values: MD -0.12 (95% CI -0.20 to -0.04) (Analysis 4.10) at six months, -0.14 (95% CI -0.22 to -0.06) (Analysis 4.11) at nine months, and -0.02 (95% CI -0.10 to +0.06) (Analysis 4.12) at 12 months. Mean weight-for-length z-scores were high and rose (from about 0.65 to 0.80) from six to 12 months, with no significant differences between the EBF and MBF groups at any age: MD +0.02 (95% CI -0.07 to +0.11) (Analysis 4.13) at six months, +0.03 (95% CI -0.06 to +0.12) (Analysis 4.14) at nine months, and -0.08 (95% CI -0.17 to +0.01) (Analysis 4.15 at 12 months.

The prevalence of low (less than -2) z-scores did not differ significantly in the two Belarusian feeding groups for any of the three z-scores at any of the three ages, although the small number of infants with low z-scores provided low statistical power to detect such differences. RRs (and 95% CIs) for low weight-for-age were 0.92 (0.04 to 19.04) (Analysis 4.16) at six months, 1.52 (0.16 to 14.62) (Analysis 4.17) at nine months and 1.15 (0.13 to 10.31) (Analysis 4.18) at 12 months. For length-for-age, the corresponding figures were 1.53 (0.84 to 2.78) at six months (Analysis 4.19), 1.46 (0.80 to 2.64) (Analysis 4.20) at nine months, and 0.66 (0.23 to 1.87) (Analysis 4.21) at 12 months. For weight-for-length, the figures were 0.31 (0.02 to 5.34) (Analysis 4.22) at six months, 1.14 (0.24 to 5.37) (Analysis 4.23) at nine months, and 1.15 (0.13 to 10.31) (Analysis 4.24) at 12 months.

The Belarusian study also provided data on head circumference. No significant differences were observed at six months (difference 0.19 (95% CI 0.06 to 0.32) cm) (Analysis 4.25) or nine months (0.07 (95% CI -0.06 to 0.20) cm) (Analysis 4.26), but the EBF group had a slightly but significantly larger circumference at 12 months (Analysis 4.27): difference = 0.19 (95% CI 0.06 to 0.32) cm.

Heinig 1993 reported nearly identical sleeping time (729 versus 728 minutes/day) in the two groups (Analysis 4.28). Akeson 1996a reported similar total amino acid and essential amino acid concentrations at six months of age in the two feeding groups (Analysis 4.29; Analysis 4.30). Both Kramer 2000a and a cohort study from Finland (Kajosaari 1983) reported on atopic eczema at one year (Analysis 4.31). The two studies showed substantial (I2 = 78%) heterogeneity, with Kajosaari 1983 reporting a significantly reduced risk, but the larger Belarusian study finding a much lower absolute risk in both feeding groups and no risk reduction with EBF; the pooled random-effects average RR was 0.65 (0.27, 1.59) (Analysis 4.31). Although Kajosaari 1983 also reported a reduced risk of a history of food allergy (Analysis 4.32), double food challenges showed no significant risk reduction (RR 0.77; 95% CI 0.25 to 2.41) (Analysis 4.33). Neither Oddy 1999 nor Kramer 2000a found a significant reduction in risk of recurrent (two or more episodes) wheezing in the EBF group (pooled RR 0.79; 95% CI 0.49 to 1.28) (Analysis 4.34).

A small Italian study of hematologic outcomes at 12 months by Pisacane in 1995 reported a statistically significantly higher hemoglobin concentration (117 versus 109 g/L (95% CI for the difference = +4.03 to +11.97 g/L)) (Analysis 4.35), a nonsignificant reduction in anemia (hemoglobin less than 110 g/L) (RR 0.12; 95% CI 0.01 to 1.80) (Analysis 4.36), a nonsignificantly higher ferritin concentration (MD +4.70; 95% CI -6.30 to +15.70 mcg/L) (Analysis 4.37), and a nonsignificant reduction in the risk of low (less than 10 mcg/L) ferritin concentration (RR 0.42; 95% CI 0.12 to 1.54) (Analysis 4.38) among infants in the EBF group. Of note in this study is that the exclusive and mixed breastfeeding continued in both groups until at least 12 months (a criterion for selection into the Pisacane 1995 study).

In the Belarusian study (Kramer 2000a), the EBF group had a significantly reduced risk of one or more episodes of gastrointestinal infection in the first 12 months of life (RR 0.67; 95% CI 0.46 to 0.97) (Analysis 4.39), which was maintained in a multivariate mixed model controlling for geographic origin, urban versus rural location, maternal education, and number of siblings in the household (adjusted OR 0.61; 95% CI 0.41 to 0.93). Importantly, when a mixed-level, multivariate Poisson model was used to estimate the adjusted incidence density ratio (IDR) by age period. From zero to three months (when both groups were exclusively breastfed), the IDR was 0.97 (95% CI 0.46 to 2.04), while at three to six months (when the feeding differed), the protective effect of EBF was strong (IDR 0.35: 95% CI 0.13 to 0.96). No significant reduction in risk was observed for hospitalization for gastrointestinal infection, however (RR 0.79; 95% CI 0.42 to 1.49) (Analysis 4.40). In the above-mentioned Australian cohort study, Oddy 1999 found no significant reduction of risk for one or more episodes of upper respiratory tract infection (Analysis 4.41) in the EBF group (RR 1.07; 95% CI 0.96 to 1.20). Neither Oddy 1999 nor Kramer 2000a found a significantly reduced risk of two or more such episodes (pooled RR 0.91; 95% CI 0.82 to 1.02) (Analysis 4.42). Nor did Oddy 1999 find a significant reduction in risk of four or more episodes of upper respiratory infection (RR 0.82; 95% CI 0.52 to 1.29) (Analysis 4.43) or of one or more episodes of lower respiratory tract infection (RR 1.07; 95% CI 0.86 to 1.33) (Analysis 4.44). Kramer 2000a found a small and nonsignificant reduction in risk of two or more respiratory tract infections (upper and lower combined) (RR 0.90; 95% CI 0.79 to 1.03) (Analysis 4.45). Duijts 2010 reported substantially lower adjusted odds ratios (versus a never-breastfed group) for both upper and lower respiratory tract infection in their EBF group compared with their MBF group in the first six months of life but not for months seven to 12 (data not shown). The combined crude results of Oddy 1999 and Kramer 2000a show a substantial and statistically significant reduction in risk for hospitalization for respiratory tract infection (pooled RR 0.75; 95% CI 0.60 to 0.94) (Analysis 4.46), but the crude risk reduction in Kramer 2000a was nearly abolished and became statistically nonsignificant in a multivariate mixed model controlling for geographic region, urban versus rural location, maternal education and cigarette smoking, and number of siblings in the household (adjusted OR 0.96; 95% CI 0.71 to 1.30). In a study from Tucson, Arizona, (Duncan 1993) reported no difference in the average number of episodes of acute otitis media in the first 12 months of life (Analysis 4.47) in the exclusive versus MBF groups (1.48 versus 1.52 episodes, respectively) (95% CI for the difference -0.49 to +0.41 episodes). Duncan 1993 and Kramer 2000a both found a slightly elevated risk for one or more episodes of otitis media (pooled RR 1.28; 95% CI 1.04 to 1.57) (Analysis 4.48), but Duncan 1993 found a nonsignificant reduction in risk for frequent otitis media (RR 0.81; 95% CI 0.43 to 1.52) (Analysis 4.49). Kramer 2000a recorded only one and two deaths (Analysis 4.50) among the 621 and 2862 Belarusian infants in the EBF and MBF groups, respectively (RR 2.30; 95% CI 0.21 to 25.37).

Reported outcomes beyond infancy have included dental caries, growth and adiposity measures, blood pressure, allergy, cognitive ability, and behaviour. Kramer 2000a reported no difference in decayed, missing, or filled teeth either in the total dentition (Analysis 4.51) or the incisors (Analysis 4.52) at age six years. At 6.5 years, no significant differences were observed for height (Analysis 4.53), leg length (Analysis 4.54), head circumference Analysis 4.55), or waist circumference (Analysis 4.59) between the EBF and MBF groups. Body mass index (BMI, Analysis 4.56), triceps (Analysis 4.57) and subscapular (Analysis 4.58) skinfold thicknesses, hip circumference (Analysis 4.60), and systolic (Analysis 4.61) and diastolic blood pressure (Analysis 4.62) were actually significantly higher in the EBF group, however, although multivariate mixed models with adjustment for clustering and for potential confounding variables yielded nonsignificant adjusted MDs for subscapular skinfold thickness [+0.2 (95% CI -0.02 to +0.5) mm], systolic blood pressure [0.0 (95% CI -1.0 to +0.9) mm Hg], and diastolic blood pressure [-0.3 (95% CI -1.2 to +0.5) mm Hg]. For allergic outcomes at ages five to seven years (Kajosaari 1983, Oddy 1999, and Kramer 2000a), no reduction in risk was observed for atopic eczema (Analysis 4.63), hay fever (Analysis 4.64), asthma (Analysis 4.65), food allergy (Analysis 4.66), allergy to animal dander (Analysis 4.67), or positive skin-prick tests (Analysis 4.68 to Analysis 4.73). Despite higher IQ scores at age 6.5 years observed in intention-to-treat analyses of the breastfeeding promotion intervention in PROBIT (Kramer 2000a), no significant differences were observed in these outcomes in observational comparisons of EBF versus MBF (Analysis 4.74 to Analysis 4.80), except for block designs (Analysis 4.77). The latter difference favouring the EBF group was no longer significant, however, in multivariate mixed models with adjustment for clustering and for potential confounding variables (adjusted MD -0.7; 95% CI -1.6 to 0.3). Teachers' ratings of the PROBIT children's academic performance at age 6.5 years (Analysis 4.81 to Analysis 4.84) were actually higher for all subjects except for mathematics (Analysis 4.83), but the differences all became statistically nonsignificant in multivariate mixed models with adjustment for clustering and for potential confounding variables. Finally, no significant differences were observed in the latter study for parents' or teachers' rating of the children's behaviour at age 6.5 years (Analysis 4.85 to Analysis 4.96).

Comparison five: observational studies of prolonged (more than six months) exclusive versus mixed breastfeeding, developed countries

A small observational cohort study from the Baltimore-Washington area (U.S.) (Ahn 1980) reported "no differences in the overall rates of gain in weight and length" for the first year of life in infants who were exclusively breastfed beyond six months versus those exclusively breastfed for less than six months and mixed breastfed thereafter. The actual data were not reported, however, and thus cannot be assessed quantitatively in this review.

One small Finnish study (Savilahti 1987a) reported no difference in lipid concentrations at nine months among infants exclusively breastfed for nine months versus those exclusively breastfed for six months and mixed breastfed from six to nine months. Similar concentrations were observed for very low density lipoprotein, low density lipoprotein, high-density lipoprotein-2, high-density lipoprotein-3, apoprotein B, and total triglycerides (Analysis 5.1 to Analysis 5.6).

Discussion

Neither the controlled clinical trials nor the observational studies (predominantly cohort studies) from either developing or developed countries suggest that infants who continue to be exclusively breastfed for six months show deficits in weight or length gain from three to seven months or thereafter. Owing to the large sample sizes required to detect modest effects on the incidence of low (less than -2) anthropometric z-scores, however, the data are insufficient to rule out a modest increase in risk of undernutrition with exclusive breastfeeding for six months and grossly inadequate to reach conclusions about the effects of prolonged (more than six months) exclusive breastfeeding.

Consistent with the results of previous observational studies, none of which met the selection criteria for this review, the large Belarussian study (Kramer 2000a) found a significant reduction in risk of one or more episodes of gastrointestinal infection. Two recent studies from Iran (Khadivzadeh 2004) and Nigeria (Onayade 2004) reported reductions in risk of both gastrointestinal and respiratory infection. Combined data from Finland, Australia, and Belarus do not suggest a protective effect against short- or long-term atopic outcomes.

The data are conflicting with respect to iron status, but the controlled trials from Honduras (Cohen 1994a; Dewey 1999a) suggest that, at least in developing-country settings where maternal iron status (and thus newborn iron stores) may be suboptimal, exclusive breastfeeding without iron supplementation may compromise hematologic status by six months of age. The reasons for the superior hematologic status reported in Italian infants exclusively breastfed for at least seven months are unclear.

Data from the two Honduran trials (Cohen 1994a; Dewey 1999a) and the Bangladeshi cohort study (Huffman 1987) suggest that exclusive breastfeeding through six months is associated with delayed resumption of menses, at least in settings with high breastfeeding frequency. The more prolonged lactational amenorrhea represents an additional advantage of continued exclusive breastfeeding in developing-country settings.

The two Honduran trials (Cohen 1994a; Dewey 1999a) also found prolonged exclusive breastfeeding to be associated with more rapid maternal postpartum weight loss. Such an effect would be an additional benefit if it were generalizable to developed-country settings where gestational weight gains and postpartum weight retention are high, but would be a disadvantage if it applied to undernourished women in developing countries.

In the two Honduran trials (Cohen 1994a; Dewey 1999a), mothers allocated to the prolonged exclusive breastfeeding group reported that their infants crawled at a significantly younger age. No such difference was seen, however, in the age at which the infants first sat from lying position, and the results for walking by 12 months differed in the two trials. The inconsistency of these results, coupled with the potential for biased maternal reporting due to nonblinding, suggest the need for cautious interpretation and further study.

Authors' conclusions

Implications for practice

Infants breastfed exclusively for six months have a reduced risk of gastrointestinal infection and no observable deficits in growth. Mothers who exclusively breastfeed for six months are more likely to remain amenorrheic for six months postpartum and to lose weight postpartum at a slightly faster rate. No benefits of introducing complementary foods between four and six months have been demonstrated, with the exception of improved iron status in one developing-country setting (Honduras). Since the latter benefit can be achieved more effectively by medicinal iron supplementation (e.g., vitamin drops), it does not appear to justify incurring the adverse effects of liquid or solid food supplementation on infectious morbidity, and lactational amenorrhea. Exclusive breastfeeding for six months does not seem to confer any long-term (at least to early school age) protection against obesity or allergic disease, nor any benefits in cognitive ability or behaviour, compared with exclusive breastfeeding for three to four months with continued partial breastfeeding to six months. Thus, with the caveat that individual infants must still be managed individually, so that insufficient growth or other adverse outcomes are not ignored and appropriate interventions are provided, the overall evidence demonstrates no apparent risks in recommending, as a general policy, exclusive breastfeeding for the first six months of life in both developing and developed-country settings. In fact, in response to the original version of this review, World Health Organization and the World Health Assembly modified its recommendations for the duration of exclusive breastfeeding (WHO 2001b).

Implications for research

The investigators involved in the two Honduran trials took a step in the right direction when they opted for an experimental design to overcome problems with confounding (particularly confounding by indication) and selection bias inherent in observational designs. The results of observational studies from developing countries are consistent with the results of the two Honduran trials, especially with respect to growth. Nonetheless, the small number of studies and of infants studied, as well as uncertainty about the net direction and magnitude of potential biases, underscore the need for further research, particularly to rule out modest differences in risk of undernutrition.

It would seem prudent, therefore, to undertake larger randomized trials of exclusive breastfeeding for six months to exclude differences in risk of malnutrition in developing countries, and to confirm the finding of reduced infectious morbidity. Because of the strong potential for contamination (similar practices among women who interact with one another), cluster randomization by clinic or even community may well be the preferred research design strategy. Longer-term (beyond early school age) impacts on health and development are also worth pursuing.

Acknowledgements

The WHO Expert Committee on the Optimal Duration of Exclusive Breastfeeding provided valuable feedback on drafts of the original version of this review. For the 2007 update, Sheila McDonald and Nisha Almeida coordinated the literature search, and Ms Almeida also carried out independent data extraction.

Data and analyses

Download statistical data

Comparison 1. Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Monthly weight gain from 4-6 months (g/mo)2265Mean Difference (IV, Fixed, 95% CI)20.78 [-21.99, 63.54]
2 Monthly weight gain from 6-12 months (g/mo)2233Mean Difference (IV, Fixed, 95% CI)-2.62 [-25.85, 20.62]
3 Monthly length gain 4-6 months (cm/mo)2265Mean Difference (IV, Fixed, 95% CI)0.10 [-0.04, 0.24]
4 Monthly length gain 6-12 months (cm/mo)2233Mean Difference (IV, Fixed, 95% CI)-0.04 [-0.10, 0.02]
5 Weight-for-age z-score at 6 months2260Mean Difference (IV, Fixed, 95% CI)0.18 [-0.06, 0.41]
6 Length-for-age z-score at 6 months2260Mean Difference (IV, Fixed, 95% CI)0.11 [-0.11, 0.33]
7 Weight-for-length z-score at 6 months2260Mean Difference (IV, Fixed, 95% CI)0.09 [-0.13, 0.31]
8 Weight-for-age z-score < -2 at 6 months2260Risk Ratio (M-H, Fixed, 95% CI)2.14 [0.74, 6.24]
9 Length-for-age z-score < -2 at 6 months2260Risk Ratio (M-H, Fixed, 95% CI)1.18 [0.56, 2.50]
10 Weight-for-length z-score < -2 at 6 months2260Risk Ratio (M-H, Fixed, 95% CI)1.38 [0.17, 10.98]
11 Receipt of Fe supplements 6-9 months1139Risk Ratio (M-H, Fixed, 95% CI)1.20 [0.91, 1.58]
12 Hemoglobin concentration (g/L) at 6 months1139Mean Difference (IV, Fixed, 95% CI)-5.0 [-8.46, -1.54]
13 Hemoglobin concentration < 110 g/L at 6 months1139Risk Ratio (M-H, Fixed, 95% CI)1.20 [0.91, 1.58]
14 Hemoglobin concentration < 103 g/L at 6 months1139Risk Ratio (M-H, Fixed, 95% CI)1.29 [0.75, 2.23]
15 Hematocrit (%) at 6 months1139Mean Difference (IV, Fixed, 95% CI)-1.20 [-2.15, -0.25]
16 Hematocrit < 33% at 6 months1139Risk Ratio (M-H, Fixed, 95% CI)1.50 [0.85, 2.64]
17 Plasma ferritin concentration (mcg/L) at 6 months1135Mean Difference (IV, Fixed, 95% CI)-18.9 [-37.31, -0.49]
18 Plasma ferritin concentration < 12 mcg/L at 6 months1135Risk Ratio (M-H, Fixed, 95% CI)2.34 [0.86, 6.35]
19 Plasma ferritin concentration < 15 mcg/L at 6 months1135Risk Ratio (M-H, Fixed, 95% CI)2.93 [1.13, 7.56]
20 Plasma zinc concentration < 70 mcg/dL at 6 months1101Risk Ratio (M-H, Fixed, 95% CI)0.75 [0.43, 1.33]
21 % of days with fever 4-6 months2260Mean Difference (IV, Fixed, 95% CI)0.26 [-1.29, 1.81]
22 % of days with cough 4-6 months2260Mean Difference (IV, Random, 95% CI)2.33 [-6.00, 12.65]
23 % of days with nasal congestion 4-6 months2260Mean Difference (IV, Fixed, 95% CI)0.11 [-4.41, 4.63]
24 % of days with nasal discharge 4-6 months2260Mean Difference (IV, Random, 95% CI)-0.72 [-6.81, 5.38]
25 % of days with hoarseness 4-6 months2260Mean Difference (IV, Fixed, 95% CI)-0.19 [-1.17, 0.79]
26 % of days with diarrhea 4-6 months2260Mean Difference (IV, Fixed, 95% CI)1.15 [-0.35, 2.65]
27 % of days with fever 6-12 months2258Mean Difference (IV, Fixed, 95% CI)-0.39 [-2.80, 2.02]
28 % of days with nasal congestion 6-12 months2258Mean Difference (IV, Fixed, 95% CI)3.11 [-0.12, 6.35]
29 % of days with diarrhea 6-12 months2258Mean Difference (IV, Fixed, 95% CI)-0.74 [-2.34, 0.86]
30 Age first crawled (mo)2240Mean Difference (IV, Fixed, 95% CI)-0.80 [-1.26, -0.34]
31 Age first sat from lying position (mo)2238Mean Difference (IV, Random, 95% CI)-0.22 [-0.91, 0.46]
32 Did not walk by 12 months2233Risk Ratio (M-H, Random, 95% CI)0.88 [0.50, 1.55]
33 Maternal postpartum weight loss 4-6 months (kg)2260Mean Difference (IV, Fixed, 95% CI)0.42 [0.02, 0.82]
34 Maternal resumption of menses 6 months postpartum2189Risk Ratio (M-H, Fixed, 95% CI)0.58 [0.33, 1.03]
Analysis 1.1.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 1 Monthly weight gain from 4-6 months (g/mo).

Analysis 1.2.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 2 Monthly weight gain from 6-12 months (g/mo).

Analysis 1.3.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 3 Monthly length gain 4-6 months (cm/mo).

Analysis 1.4.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 4 Monthly length gain 6-12 months (cm/mo).

Analysis 1.5.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 5 Weight-for-age z-score at 6 months.

Analysis 1.6.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 6 Length-for-age z-score at 6 months.

Analysis 1.7.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 7 Weight-for-length z-score at 6 months.

Analysis 1.8.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 8 Weight-for-age z-score < -2 at 6 months.

Analysis 1.9.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 9 Length-for-age z-score < -2 at 6 months.

Analysis 1.10.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 10 Weight-for-length z-score < -2 at 6 months.

Analysis 1.11.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 11 Receipt of Fe supplements 6-9 months.

Analysis 1.12.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 12 Hemoglobin concentration (g/L) at 6 months.

Analysis 1.13.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 13 Hemoglobin concentration < 110 g/L at 6 months.

Analysis 1.14.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 14 Hemoglobin concentration < 103 g/L at 6 months.

Analysis 1.15.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 15 Hematocrit (%) at 6 months.

Analysis 1.16.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 16 Hematocrit < 33% at 6 months.

Analysis 1.17.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 17 Plasma ferritin concentration (mcg/L) at 6 months.

Analysis 1.18.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 18 Plasma ferritin concentration < 12 mcg/L at 6 months.

Analysis 1.19.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 19 Plasma ferritin concentration < 15 mcg/L at 6 months.

Analysis 1.20.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 20 Plasma zinc concentration < 70 mcg/dL at 6 months.

Analysis 1.21.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 21 % of days with fever 4-6 months.

Analysis 1.22.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 22 % of days with cough 4-6 months.

Analysis 1.23.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 23 % of days with nasal congestion 4-6 months.

Analysis 1.24.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 24 % of days with nasal discharge 4-6 months.

Analysis 1.25.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 25 % of days with hoarseness 4-6 months.

Analysis 1.26.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 26 % of days with diarrhea 4-6 months.

Analysis 1.27.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 27 % of days with fever 6-12 months.

Analysis 1.28.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 28 % of days with nasal congestion 6-12 months.

Analysis 1.29.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 29 % of days with diarrhea 6-12 months.

Analysis 1.30.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 30 Age first crawled (mo).

Analysis 1.31.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 31 Age first sat from lying position (mo).

Analysis 1.32.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 32 Did not walk by 12 months.

Analysis 1.33.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 33 Maternal postpartum weight loss 4-6 months (kg).

Analysis 1.34.

Comparison 1 Exclusive breastfeeding for 6 versus 4 months, developing countries, controlled trials, Outcome 34 Maternal resumption of menses 6 months postpartum.

Comparison 2. Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Monthly weight gain 4-6 months (g/mo)41803Mean Difference (IV, Fixed, 95% CI)-10.10 [-27.68, 7.48]
2 Monthly weight gain 6-9 months (g/mo)1319Mean Difference (IV, Fixed, 95% CI)-6.0 [-54.15, 42.15]
3 Monthly length gain 4-6 months (cm/mo)41803Mean Difference (IV, Fixed, 95% CI)0.04 [-0.02, 0.11]
4 Monthly length gain 6-9 months (cm/mo)1319Mean Difference (IV, Fixed, 95% CI)0.04 [-0.06, 0.14]
5 Weight-for-age z-score at 6-7 months1370Mean Difference (IV, Fixed, 95% CI)0.13 [-0.09, 0.35]
6 Weight-for-age z-score at 9-10 months1319Mean Difference (IV, Fixed, 95% CI)0.09 [-0.15, 0.33]
7 Length-for-age z-score at 6-7 months1370Mean Difference (IV, Fixed, 95% CI)0.04 [-0.14, 0.22]
8 Length-for-age z-score at 9-10 months1319Mean Difference (IV, Fixed, 95% CI)0.11 [-0.09, 0.31]
9 Weight-for-length z-score at 6-7 months1370Mean Difference (IV, Fixed, 95% CI)0.11 [-0.09, 0.31]
10 Weight-for-length z-score at 9-10 months1319Mean Difference (IV, Fixed, 95% CI)0.01 [-0.21, 0.23]
11 Weight-for-age z-score < -2 at 6-7 months1370Risk Ratio (M-H, Fixed, 95% CI)0.92 [0.54, 1.58]
12 Weight-for-age z-score < -2 at 9-10 months1319Risk Ratio (M-H, Fixed, 95% CI)0.93 [0.64, 1.36]
13 Length-for-age z-score < -2 at 6-7 months1370Risk Ratio (M-H, Fixed, 95% CI)1.20 [0.57, 2.53]
14 Length-for-age z-score < -2 at 9-10 months1319Risk Ratio (M-H, Fixed, 95% CI)1.21 [0.62, 2.37]
15 Weight-for-length z-score < -2 at 6-7 months1370Risk Ratio (M-H, Fixed, 95% CI)0.42 [0.12, 1.50]
16 Weight-for-length z-score < -2 at 9-10 months1319Risk Ratio (M-H, Fixed, 95% CI)0.82 [0.39, 1.71]
17 Mid-upper arm circumference at 6-7 months (cm)1370Mean Difference (IV, Fixed, 95% CI)0.20 [-0.04, 0.44]
18 Mid-upper arm circumference at 9-10 months (cm)1319Mean Difference (IV, Fixed, 95% CI)0.10 [-0.16, 0.36]
19 One or more episodes of gastrointestinal infection at 4-6 months1193Risk Ratio (M-H, Fixed, 95% CI)0.41 [0.21, 0.78]
20 One or more episodes of respiratory infection at 4-6 months1193Risk Ratio (M-H, Fixed, 95% CI)0.68 [0.43, 1.06]
21 Resumption of menses by 6-7 months postpartum1686Risk Ratio (M-H, Fixed, 95% CI)0.19 [0.05, 0.79]
Analysis 2.1.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 1 Monthly weight gain 4-6 months (g/mo).

Analysis 2.2.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 2 Monthly weight gain 6-9 months (g/mo).

Analysis 2.3.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 3 Monthly length gain 4-6 months (cm/mo).

Analysis 2.4.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 4 Monthly length gain 6-9 months (cm/mo).

Analysis 2.5.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 5 Weight-for-age z-score at 6-7 months.

Analysis 2.6.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 6 Weight-for-age z-score at 9-10 months.

Analysis 2.7.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 7 Length-for-age z-score at 6-7 months.

Analysis 2.8.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 8 Length-for-age z-score at 9-10 months.

Analysis 2.9.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 9 Weight-for-length z-score at 6-7 months.

Analysis 2.10.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 10 Weight-for-length z-score at 9-10 months.

Analysis 2.11.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 11 Weight-for-age z-score < -2 at 6-7 months.

Analysis 2.12.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 12 Weight-for-age z-score < -2 at 9-10 months.

Analysis 2.13.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 13 Length-for-age z-score < -2 at 6-7 months.

Analysis 2.14.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 14 Length-for-age z-score < -2 at 9-10 months.

Analysis 2.15.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 15 Weight-for-length z-score < -2 at 6-7 months.

Analysis 2.16.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 16 Weight-for-length z-score < -2 at 9-10 months.

Analysis 2.17.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 17 Mid-upper arm circumference at 6-7 months (cm).

Analysis 2.18.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 18 Mid-upper arm circumference at 9-10 months (cm).

Analysis 2.19.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 19 One or more episodes of gastrointestinal infection at 4-6 months.

Analysis 2.20.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 20 One or more episodes of respiratory infection at 4-6 months.

Analysis 2.21.

Comparison 2 Exclusive breastfeeding for 6-7 versus 3-4 months, developing countries, observational studies, Outcome 21 Resumption of menses by 6-7 months postpartum.

Comparison 3. Exclusive breastfeeding for > 6 months versus 6 months, developing countries, observational studies
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Weight-for-age < 75% of reference mean131Risk Ratio (M-H, Fixed, 95% CI)0.61 [0.26, 1.43]
Analysis 3.1.

Comparison 3 Exclusive breastfeeding for > 6 months versus 6 months, developing countries, observational studies, Outcome 1 Weight-for-age < 75% of reference mean.

Comparison 4. Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Monthly weight gain 3-8 months (g/mo)44388Mean Difference (IV, Random, 95% CI)-7.95 [-31.84, 15.93]
2 Monthly weight gain 6-9 months (g/mo)23432Mean Difference (IV, Random, 95% CI)21.11 [-44.70, 86.91]
3 Monthly weight gain 8-12 months (g/mo)33450Mean Difference (IV, Fixed, 95% CI)-1.82 [-16.72, 13.08]
4 Monthly length gain 3-8 months (cm/mo)44385Mean Difference (IV, Random, 95% CI)-0.03 [-0.11, 0.06]
5 Monthly length gain 6-9 months (cm/mo)23430Mean Difference (IV, Fixed, 95% CI)-0.04 [-0.10, 0.01]
6 Monthly length gain 8-12 months (cm/mo)33448Mean Difference (IV, Fixed, 95% CI)0.09 [0.03, 0.14]
7 Weight-for-age z-score at 6 months13455Mean Difference (IV, Fixed, 95% CI)-0.09 [-0.16, -0.02]
8 Weight-for-age z-score at 9 months13400Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.18, -0.02]
9 Weight-for-age z-score at 12 months13458Mean Difference (IV, Fixed, 95% CI)-0.09 [-0.17, -0.01]
10 Length-for-age z-score at 6 months13454Mean Difference (IV, Fixed, 95% CI)-0.12 [-0.20, -0.04]
11 Length-for-age z-score at 9 months13398Mean Difference (IV, Fixed, 95% CI)-0.14 [-0.22, -0.06]
12 Length-for-age z-score at 12 months13458Mean Difference (IV, Fixed, 95% CI)-0.02 [-0.10, 0.06]
13 Weight-for-length z-score at 6 months13454Mean Difference (IV, Fixed, 95% CI)0.02 [-0.07, 0.11]
14 Weight-for-length z-score at 9 months13398Mean Difference (IV, Fixed, 95% CI)0.03 [-0.06, 0.12]
15 Weight-for-length z-score at 12 months13458Mean Difference (IV, Fixed, 95% CI)-0.08 [-0.17, 0.01]
16 Weight-for-age z-score < -2 at 6 months13461Risk Ratio (M-H, Fixed, 95% CI)0.92 [0.04, 19.04]
17 Weight-for-age z-score < -2 at 9 months13408Risk Ratio (M-H, Fixed, 95% CI)1.52 [0.16, 14.62]
18 Weight-for-age z-score < -2 at 12 months13466Risk Ratio (M-H, Fixed, 95% CI)1.15 [0.13, 10.31]
19 Length-for-age z-score < -2 at 6 months13460Risk Ratio (M-H, Fixed, 95% CI)1.53 [0.84, 2.78]
20 Length-for-age z-score < -2 at 9 months13406Risk Ratio (M-H, Fixed, 95% CI)1.46 [0.80, 2.64]
21 Length-for-age z-score < -2 at 12 months13466Risk Ratio (M-H, Fixed, 95% CI)0.66 [0.23, 1.87]
22 Weight-for-length z-score < -2 at 6 months13460Risk Ratio (M-H, Fixed, 95% CI)0.31 [0.02, 5.34]
23 Weight-for-length z-score < -2 at 9 months13406Risk Ratio (M-H, Fixed, 95% CI)1.14 [0.24, 5.37]
24 Weight-for-length z-score < -2 at 12 months13466Risk Ratio (M-H, Fixed, 95% CI)1.15 [0.13, 10.31]
25 Head circumference at 6 months (cm)13440Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.23, 0.03]
26 Head circumference at 9 months (cm)13389Mean Difference (IV, Fixed, 95% CI)0.07 [-0.06, 0.20]
27 Head circumference at 12 months (cm)13450Mean Difference (IV, Fixed, 95% CI)0.19 [0.06, 0.32]
28 Sleeping time at 9 months (min/day)150Mean Difference (IV, Fixed, 95% CI)1.0 [-36.65, 38.65]
29 Total essential amino acid concentration (umol/L) at 6 months144Mean Difference (IV, Fixed, 95% CI)22.0 [-59.60, 103.60]
30 Total amino acid concentration (umol/L) at 6 months144Mean Difference (IV, Fixed, 95% CI)73.0 [-118.22, 264.22]
31 Atopic eczema in first 12 months23618Risk Ratio (M-H, Random, 95% CI)0.65 [0.27, 1.59]
32 Food allergy at 1 year (by history)1135Risk Ratio (M-H, Fixed, 95% CI)0.19 [0.08, 0.48]
33 Food allergy at 1 year (by double challenge)1135Risk Ratio (M-H, Fixed, 95% CI)0.77 [0.25, 2.41]
34 Two or more episodes of wheezing in first 12 months23993Risk Ratio (M-H, Fixed, 95% CI)0.79 [0.49, 1.28]
35 Hemoglobin concentration (g/L) at 12 months130Mean Difference (IV, Fixed, 95% CI)8.0 [4.03, 11.97]
36 Hemoglobin concentration < 110 g/L at 12 months130Risk Ratio (M-H, Fixed, 95% CI)0.12 [0.01, 1.80]
37 Serum ferritin concentration (mcg/L) at 12 months130Mean Difference (IV, Fixed, 95% CI)4.70 [-6.30, 15.70]
38 Serum ferritin concentration < 10 mcg/L at 12 months130Risk Ratio (M-H, Fixed, 95% CI)0.42 [0.12, 1.54]
39 One or more episodes of gastrointestinal infection in first 12 months13483Risk Ratio (M-H, Fixed, 95% CI)0.67 [0.46, 0.97]
40 Hospitalization for gastrointestinal infection in first 12 months13483Risk Ratio (M-H, Fixed, 95% CI)0.79 [0.42, 1.49]
41 One or more episodes of upper respiratory tract infection in first 12 months1510Risk Ratio (M-H, Fixed, 95% CI)1.07 [0.96, 1.20]
42 Two or more episodes of upper respiratory tract infection in first 12 months23993Risk Ratio (M-H, Fixed, 95% CI)0.91 [0.82, 1.02]
43 Four or more episodes of upper respiratory tract infection in first 12 months1510Risk Ratio (M-H, Fixed, 95% CI)0.82 [0.52, 1.29]
44 One or more episodes of lower respiratory tract infection in first 12 months1510Risk Ratio (M-H, Fixed, 95% CI)1.07 [0.86, 1.33]
45 Two or more episodes of respiratory tract infection (upper or lower) in first 12 months13483Risk Ratio (M-H, Fixed, 95% CI)0.90 [0.79, 1.03]
46 Hospitalization for respiratory tract infection in first 12 months23993Risk Ratio (M-H, Fixed, 95% CI)0.75 [0.60, 0.94]
47 Number of episodes of otitis media in first 12 months1279Mean Difference (IV, Fixed, 95% CI)-0.04 [-0.49, 0.41]
48 One or more episodes of otitis media in first 12 months23762Risk Ratio (M-H, Fixed, 95% CI)1.28 [1.04, 1.57]
49 Frequent otitis media in first 12 months1279Risk Ratio (M-H, Fixed, 95% CI)0.81 [0.43, 1.52]
50 Death in first 12 months13483Risk Ratio (M-H, Fixed, 95% CI)2.30 [0.21, 25.37]
51 Any dental caries (decayed, missing, or filled teeth) at 6 years12948Risk Ratio (M-H, Fixed, 95% CI)0.98 [0.94, 1.03]
52 Any incisor caries (decayed, missing, or filled teeth) at 6 years12948Odds Ratio (M-H, Fixed, 95% CI)0.91 [0.72, 1.16]
53 Height at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.10 [-0.40, 0.60]
54 Leg length at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.20 [-0.14, 0.54]
55 Head circumference at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.10 [-0.04, 0.24]
56 BMI at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.20 [0.02, 0.38]
57 Triceps skinfold thickness at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.90 [0.51, 1.29]
58 Subscapular skinfold thickness12951Mean Difference (IV, Fixed, 95% CI)0.5 [0.25, 0.75]
59 Waist circumference at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.0 [-0.42, 0.42]
60 Hip circumference at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)0.5 [0.05, 0.95]
61 Systolic blood pressure at 6.5 years12951Mean Difference (IV, Fixed, 95% CI)1.30 [0.39, 2.21]
62 Diastolic blood pressure at 6.5 years (mm Hg)12951Mean Difference (IV, Fixed, 95% CI)1.0 [0.29, 1.71]
63 Atopic eczema at 5-7 years23584Risk Ratio (M-H, Fixed, 95% CI)0.86 [0.47, 1.58]
64 Hay fever at 5-7 years23584Risk Ratio (M-H, Random, 95% CI)0.80 [0.39, 1.65]
65 Asthma at 5-7 years34023Risk Ratio (M-H, Fixed, 95% CI)1.02 [0.72, 1.44]
66 Food allergy at 5 years1113Risk Ratio (M-H, Fixed, 95% CI)0.61 [0.12, 3.19]
67 Allergy to animal dander at 5 years1113Risk Ratio (M-H, Fixed, 95% CI)0.81 [0.24, 2.72]
68 Positive skin-prick test to house dust mite at 6.5 years12320Odds Ratio (M-H, Fixed, 95% CI)0.86 [0.62, 1.20]
69 Positive skin-prick test to cat dander at 6.5 years12320Odds Ratio (M-H, Fixed, 95% CI)0.86 [0.60, 1.24]
70 Positive skin-prick test to birch pollen at 6.5 years12320Odds Ratio (M-H, Fixed, 95% CI)0.80 [0.55, 1.18]
71 Positive skin-prick test to mixed northern grasses at 6.5 years12320Odds Ratio (M-H, Fixed, 95% CI)0.71 [0.50, 1.01]
72 Positive skin-prick test to Alternaria at 6.5 years12320Odds Ratio (M-H, Fixed, 95% CI)0.74 [0.47, 1.17]
73 Any positive skin-prick test at 6-7 years22651Risk Ratio (M-H, Fixed, 95% CI)0.95 [0.81, 1.11]
74 Wechsler cognitive ability test at 6.5 years: vocabulary12944Mean Difference (IV, Fixed, 95% CI)0.5 [-0.57, 1.57]
75 Wechsler cognitive ability test at 6.5 years: similarities12944Mean Difference (IV, Fixed, 95% CI)0.30 [-0.56, 1.16]
76 Wechsler cognitive ability test at 6.5 years: matrices12944Mean Difference (IV, Fixed, 95% CI)-0.20 [-1.07, 0.67]
77 Wechsler cognitive ability test at 6.5 years: block designs12944Mean Difference (IV, Fixed, 95% CI)1.30 [0.40, 2.20]
78 Wechsler cognitive ability test at 6.5 years: verbal IQ12944Mean Difference (IV, Fixed, 95% CI)0.5 [-0.95, 1.95]
79 Wechsler cognitive ability test at 6.5 years: performance IQ12944Mean Difference (IV, Fixed, 95% CI)0.80 [-0.55, 2.15]
80 Wechsler cognitive ability test at 6.5 years: full-scale IQ12944Mean Difference (IV, Fixed, 95% CI)0.80 [-0.58, 2.18]
81 Teacher's academic rating at 6.5 years: reading12196Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.19, -0.01]
82 Teacher's academic rating at 6.5 years: writing12196Mean Difference (IV, Fixed, 95% CI)-0.12 [-0.20, -0.04]
83 Teacher's academic rating at 6.5 years: mathematics12196Mean Difference (IV, Fixed, 95% CI)-0.04 [-0.12, 0.04]
84 Teacher's academic rating at 6.5 years: other subjects12196Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.17, -0.03]
85 Parent's behavior rating at 6.5 years: total difficulties12941Mean Difference (IV, Fixed, 95% CI)0.30 [-0.16, 0.76]
86 Parent's behavior rating at 6.5 years: emotional symptoms12941Mean Difference (IV, Fixed, 95% CI)0.10 [-0.09, 0.29]
87 Parent's behavior rating at 6.5 years: conduct problems12941Mean Difference (IV, Fixed, 95% CI)0.0 [-0.13, 0.13]
88 Parent's behavior rating at 6.5 years: hyperactivity/inattention12941Mean Difference (IV, Fixed, 95% CI)0.20 [-0.01, 0.41]
89 Parent's behavior rating at 6.5 years: peer problems12941Mean Difference (IV, Fixed, 95% CI)0.10 [-0.05, 0.25]
90 Parent's behavior rating at 6.5 years: prosocial behavior12941Mean Difference (IV, Fixed, 95% CI)0.10 [-0.05, 0.25]
91 Teacher's behavior rating at 6.5 years: total difficulties12525Mean Difference (IV, Fixed, 95% CI)0.10 [-0.46, 0.66]
92 Teacher's behavior rating at 6.5 years: emotional symptoms12525Mean Difference (IV, Fixed, 95% CI)0.0 [-0.18, 0.18]
93 Teacher's behavior rating at 6.5 years: conduct problems12525Mean Difference (IV, Fixed, 95% CI)0.0 [-0.17, 0.17]
94 Teacher's behavior rating at 6.5 years: hyperactivity/inattention12525Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.37, 0.17]
95 Teacher's behavior rating at 6.5 years: peer problems12525Mean Difference (IV, Fixed, 95% CI)0.10 [-0.08, 0.28]
96 Teacher's behavior rating at 6.5 years: prosocial behavior12525Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.33, 0.13]
Analysis 4.1.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 1 Monthly weight gain 3-8 months (g/mo).

Analysis 4.2.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 2 Monthly weight gain 6-9 months (g/mo).

Analysis 4.3.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 3 Monthly weight gain 8-12 months (g/mo).

Analysis 4.4.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 4 Monthly length gain 3-8 months (cm/mo).

Analysis 4.5.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 5 Monthly length gain 6-9 months (cm/mo).

Analysis 4.6.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 6 Monthly length gain 8-12 months (cm/mo).

Analysis 4.7.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 7 Weight-for-age z-score at 6 months.

Analysis 4.8.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 8 Weight-for-age z-score at 9 months.

Analysis 4.9.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 9 Weight-for-age z-score at 12 months.

Analysis 4.10.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 10 Length-for-age z-score at 6 months.

Analysis 4.11.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 11 Length-for-age z-score at 9 months.

Analysis 4.12.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 12 Length-for-age z-score at 12 months.

Analysis 4.13.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 13 Weight-for-length z-score at 6 months.

Analysis 4.14.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 14 Weight-for-length z-score at 9 months.

Analysis 4.15.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 15 Weight-for-length z-score at 12 months.

Analysis 4.16.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 16 Weight-for-age z-score < -2 at 6 months.

Analysis 4.17.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 17 Weight-for-age z-score < -2 at 9 months.

Analysis 4.18.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 18 Weight-for-age z-score < -2 at 12 months.

Analysis 4.19.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 19 Length-for-age z-score < -2 at 6 months.

Analysis 4.20.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 20 Length-for-age z-score < -2 at 9 months.

Analysis 4.21.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 21 Length-for-age z-score < -2 at 12 months.

Analysis 4.22.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 22 Weight-for-length z-score < -2 at 6 months.

Analysis 4.23.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 23 Weight-for-length z-score < -2 at 9 months.

Analysis 4.24.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 24 Weight-for-length z-score < -2 at 12 months.

Analysis 4.25.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 25 Head circumference at 6 months (cm).

Analysis 4.26.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 26 Head circumference at 9 months (cm).

Analysis 4.27.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 27 Head circumference at 12 months (cm).

Analysis 4.28.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 28 Sleeping time at 9 months (min/day).

Analysis 4.29.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 29 Total essential amino acid concentration (umol/L) at 6 months.

Analysis 4.30.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 30 Total amino acid concentration (umol/L) at 6 months.

Analysis 4.31.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 31 Atopic eczema in first 12 months.

Analysis 4.32.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 32 Food allergy at 1 year (by history).

Analysis 4.33.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 33 Food allergy at 1 year (by double challenge).

Analysis 4.34.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 34 Two or more episodes of wheezing in first 12 months.

Analysis 4.35.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 35 Hemoglobin concentration (g/L) at 12 months.

Analysis 4.36.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 36 Hemoglobin concentration < 110 g/L at 12 months.

Analysis 4.37.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 37 Serum ferritin concentration (mcg/L) at 12 months.

Analysis 4.38.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 38 Serum ferritin concentration < 10 mcg/L at 12 months.

Analysis 4.39.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 39 One or more episodes of gastrointestinal infection in first 12 months.

Analysis 4.40.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 40 Hospitalization for gastrointestinal infection in first 12 months.

Analysis 4.41.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 41 One or more episodes of upper respiratory tract infection in first 12 months.

Analysis 4.42.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 42 Two or more episodes of upper respiratory tract infection in first 12 months.

Analysis 4.43.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 43 Four or more episodes of upper respiratory tract infection in first 12 months.

Analysis 4.44.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 44 One or more episodes of lower respiratory tract infection in first 12 months.

Analysis 4.45.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 45 Two or more episodes of respiratory tract infection (upper or lower) in first 12 months.

Analysis 4.46.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 46 Hospitalization for respiratory tract infection in first 12 months.

Analysis 4.47.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 47 Number of episodes of otitis media in first 12 months.

Analysis 4.48.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 48 One or more episodes of otitis media in first 12 months.

Analysis 4.49.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 49 Frequent otitis media in first 12 months.

Analysis 4.50.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 50 Death in first 12 months.

Analysis 4.51.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 51 Any dental caries (decayed, missing, or filled teeth) at 6 years.

Analysis 4.52.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 52 Any incisor caries (decayed, missing, or filled teeth) at 6 years.

Analysis 4.53.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 53 Height at 6.5 years.

Analysis 4.54.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 54 Leg length at 6.5 years.

Analysis 4.55.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 55 Head circumference at 6.5 years.

Analysis 4.56.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 56 BMI at 6.5 years.

Analysis 4.57.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 57 Triceps skinfold thickness at 6.5 years.

Analysis 4.58.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 58 Subscapular skinfold thickness.

Analysis 4.59.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 59 Waist circumference at 6.5 years.

Analysis 4.60.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 60 Hip circumference at 6.5 years.

Analysis 4.61.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 61 Systolic blood pressure at 6.5 years.

Analysis 4.62.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 62 Diastolic blood pressure at 6.5 years (mm Hg).

Analysis 4.63.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 63 Atopic eczema at 5-7 years.

Analysis 4.64.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 64 Hay fever at 5-7 years.

Analysis 4.65.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 65 Asthma at 5-7 years.

Analysis 4.66.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 66 Food allergy at 5 years.

Analysis 4.67.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 67 Allergy to animal dander at 5 years.

Analysis 4.68.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 68 Positive skin-prick test to house dust mite at 6.5 years.

Analysis 4.69.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 69 Positive skin-prick test to cat dander at 6.5 years.

Analysis 4.70.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 70 Positive skin-prick test to birch pollen at 6.5 years.

Analysis 4.71.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 71 Positive skin-prick test to mixed northern grasses at 6.5 years.

Analysis 4.72.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 72 Positive skin-prick test to Alternaria at 6.5 years.

Analysis 4.73.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 73 Any positive skin-prick test at 6-7 years.

Analysis 4.74.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 74 Wechsler cognitive ability test at 6.5 years: vocabulary.

Analysis 4.75.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 75 Wechsler cognitive ability test at 6.5 years: similarities.

Analysis 4.76.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 76 Wechsler cognitive ability test at 6.5 years: matrices.

Analysis 4.77.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 77 Wechsler cognitive ability test at 6.5 years: block designs.

Analysis 4.78.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 78 Wechsler cognitive ability test at 6.5 years: verbal IQ.

Analysis 4.79.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 79 Wechsler cognitive ability test at 6.5 years: performance IQ.

Analysis 4.80.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 80 Wechsler cognitive ability test at 6.5 years: full-scale IQ.

Analysis 4.81.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 81 Teacher's academic rating at 6.5 years: reading.

Analysis 4.82.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 82 Teacher's academic rating at 6.5 years: writing.

Analysis 4.83.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 83 Teacher's academic rating at 6.5 years: mathematics.

Analysis 4.84.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 84 Teacher's academic rating at 6.5 years: other subjects.

Analysis 4.85.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 85 Parent's behavior rating at 6.5 years: total difficulties.

Analysis 4.86.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 86 Parent's behavior rating at 6.5 years: emotional symptoms.

Analysis 4.87.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 87 Parent's behavior rating at 6.5 years: conduct problems.

Analysis 4.88.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 88 Parent's behavior rating at 6.5 years: hyperactivity/inattention.

Analysis 4.89.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 89 Parent's behavior rating at 6.5 years: peer problems.

Analysis 4.90.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 90 Parent's behavior rating at 6.5 years: prosocial behavior.

Analysis 4.91.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 91 Teacher's behavior rating at 6.5 years: total difficulties.

Analysis 4.92.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 92 Teacher's behavior rating at 6.5 years: emotional symptoms.

Analysis 4.93.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 93 Teacher's behavior rating at 6.5 years: conduct problems.

Analysis 4.94.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 94 Teacher's behavior rating at 6.5 years: hyperactivity/inattention.

Analysis 4.95.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 95 Teacher's behavior rating at 6.5 years: peer problems.

Analysis 4.96.

Comparison 4 Exclusive breastfeeding for 6-7 months versus 3-4 months, developed countries, observational studies, Outcome 96 Teacher's behavior rating at 6.5 years: prosocial behavior.

Comparison 5. Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Very low density lipoprotein concentration (mmol/L) at 9 months126Mean Difference (IV, Fixed, 95% CI)0.05 [-0.10, 0.20]
2 Low density lipoproteinconcentration (mmol/L) at 9 months126Mean Difference (IV, Fixed, 95% CI)-0.10 [-0.88, 0.68]
3 High-density lipoprotein-2 concentration (mmol/L) at 9 months126Mean Difference (IV, Fixed, 95% CI)0.08 [-0.05, 0.21]
4 High-density lipoprotein-3 concentration (mmol/L) at 9 months126Mean Difference (IV, Fixed, 95% CI)0.0 [-0.07, 0.07]
5 Apoprotein B concentration (mg/dL) at 9 months126Mean Difference (IV, Fixed, 95% CI)5.0 [-14.93, 24.93]
6 Total triglyceride concentration (mmol/L) at 9 months126Mean Difference (IV, Fixed, 95% CI)0.3 [-0.23, 0.83]
Analysis 5.1.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 1 Very low density lipoprotein concentration (mmol/L) at 9 months.

Analysis 5.2.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 2 Low density lipoproteinconcentration (mmol/L) at 9 months.

Analysis 5.3.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 3 High-density lipoprotein-2 concentration (mmol/L) at 9 months.

Analysis 5.4.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 4 High-density lipoprotein-3 concentration (mmol/L) at 9 months.

Analysis 5.5.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 5 Apoprotein B concentration (mg/dL) at 9 months.

Analysis 5.6.

Comparison 5 Exclusive breastfeeding for > 6 months versus 6 months, developed countries, observational studies, Outcome 6 Total triglyceride concentration (mmol/L) at 9 months.

Appendices

Appendix 1. Search methods used in previous versions of the review

In order to capture as many relevant studies as possible, two independent literature searches were conducted for the first version of this review: one by staff at the Nutrition Unit of the World Health Organization (WHO) and one by the authors. The search details are shown below.

The search by WHO was conducted between June and August 2000 in the following databases: MEDLINE (1966 to June 2000), OLDMEDLINE (Index Medicus previous to 1966), CINAHL (1982 to June 2000), HealthSTAR (1975 to August 2000), EBM Reviews-Best Evidence (1991 to July/August 2000), SocioFile (1974 to July 2000), Cochrane Database of Systematic Reviews (The Cochrane Library 2000, Issue 2), CAB Abstracts (1973 to July 2000), EMBASE-Psychology (1987 to 3rd Quarter, 2000), EconLit (1969 to August 2000), Index Medicus for the WHO Eastern Mediterranean (IMEMR), African Index Medicus (AIM), and LILACS (Latin American and Caribbean Health Sciences). Where applicable, the medical subject heading (MeSH) 'breast feeding,' and otherwise the free language terms 'breast-feeding,' 'breast feeding,' or 'breastfeeding' combined with 'exclusive' or 'exclusively' were used in the search strategy. The search yielded 1423 citations (MEDLINE 686, OLDMEDLINE 15, CINAHL 25, HealthSTAR 1, EBM-Best Evidence 2, SocioFile 2, Cochrane Database of Systematic Reviews 8, CAB Abstracts 680, EMBASE-Psychology 4, other databases 0). Once duplicates were removed, 1035 citations remained; these were then assessed for eligibility.

The authors' search was conducted on August 12, 2000 in the following databases: MEDLINE (1966 to June 2000), CINAHL (1982 to April 2000), HealthSTAR (1975 to August 2000), BIOSIS (1989 to 2000), CAB Abstracts (1973 to June 2000), Cochrane Database of Systematic Reviews (The Cochrane Library 2000, Issue 3), Cochrane Central Register of Controlled Trials (The Cochrane Library 2000, Issue 3), and EMBASE-Medicine (1980 to 2000). The terms 'breast feeding,' 'infant,' and 'growth,' as MeSH headings and text words, were combined in the search strategy. This search yielded a total of 2496 citations (MEDLINE yielded 1079 citations, CINAHL 75, HealthSTAR 2, BIOSIS 190, CAB 614, Cochrane Database of Systematic Reviews 25, Cochrane Controlled Trials Register 122, and EMBASE 389). Once duplicates among the databases were removed, 1845 citations remained, 1633 of which were different from the 1035 identified by the WHO search. Thus 2668 unique citations were identified by the two searches.

The literature search for the updated (2007) review was conducted in December 2006 on the same electronic databases and search terms and logic as the second search above, with the addition of the LILACS, SocioFile, and EBM Reviews-Best Evidence databases. This updated search yielded 835 additional unique citations.

The 2011 updated literature review included the same electronic databases as the 2007 update except CAB Abstracts and HealthSTAR. That database yielded 3425 additional unique citations.

For all searches, every effort was made to identify relevant non-English language articles and abstracts. Given their own backgrounds, the review authors themselves were able to determine the eligibility of articles in French, Spanish, and Japanese. For publications in other languages, two options were available. Many articles in languages other than English provided English abstracts. As such, all potentially relevant articles were obtained and checked for availability of English abstracts. If such abstracts were not available, or were available but did not provide enough information to determine their eligibility, then assistance was requested from WHO to determine their eligibility for inclusion. No article or abstract was excluded because of language of publication.

In addition to the studies found through these electronic searches, reference lists of identified articles were checked, and contacts with experts in the field were made to identify other potentially relevant published or unpublished studies. Attempts were made to contact the authors of all studies that qualified for inclusion in the review to obtain methodologic details, clarify inconsistencies, and obtain unpublished data.

Many studies were identified that either compared outcomes in infants receiving exclusive breastfeeding (EBF) versus mixed breastfeeding (MBF) or investigated the effects of age at introduction of nonbreast-milk liquid or solid foods. The vast majority of these studies were ineligible for inclusion, however, because they did not ensure EBF at least three months prior to introducing these complementary foods in the MBF group or a comparison group with EBF at least six months, or both.

We identified 41 unique citations (articles or abstracts) that met the selection criteria, comprising 22 separate studies. Of the 22 included studies, 11 were carried out in developing countries and the other 11 in developed countries.

Ten of the 41 total citations were found by both of the two original searches (Ahn 1980; Akeson 1998a; Castillo 1996; Cohen 1994b; Cohen 1995; Dewey 1996; Dewey 1998a; Dewey 1998b; Dewey 1999b; Khan 1984); 11 were identified only by the WHO search (Akeson 1998b; Duncan 1993; Heiskanen 1994; Kajosaari 1983; Kajosaari 1991; Kajosaari 1994; Kallio 1992; Oddy 1999; Pisacane 1995; Rao 1992; Savilahti 1987b); six were found only by the authors' search (Adair 1993b; Akeson 1996b; Dewey 1995; Frongillo 1997a; Heinig 1993; Simondon 1997b). Eleven additional citations were located through contacts with experts and reference lists of relevant articles (Brown 1991b; Brown 1998; Dewey 1997; Dewey 2001; Huffman 1987; Kramer 2000b; Kramer 2000c; Kramer 2001; WHO 1994b; WHO 1995; WHO 2002).

The updated literature search from December 2006 resulted in two additional studies that met the eligibility criteria (Khadivzadeh 2004; Onayade 2004), plus a new citation from one of the original included studies (Simondon 2003).

Appendix 2. Search methods used for the current review

MEDLINE (1 January 2007 to 14 June 2011)

1     exp Breast Feeding/
2     ((breastfe$ or breast-fe$) adj4 (alone or only or exclusive$)).ti,ab.
3     exclusive*.ti,ab.
4     1 and 3
5     2 or 4

EMBASE (1 January 2007 to 14 June 2011)

1.      exp BREAST FEEDING/
2.      exclusive*.ti,ab
3.      ((breastfe* OR breast-fe*) adj4 (exclusive* OR alone OR only)).ti,ab
4.      1 AND 2
5. 3 OR 4

The Cochrane Library (2011, Issue 6)

BIOSIS (1 January 2007 to 14 June 2011)

#9 #8 AND #5  

#8 #7 OR #6  

#7 TS=exclusive* or TS=only or TS=alone  

#6 TI=exclusive* or TI=only or TI=alone  

#5 #4 OR #3 OR #2 OR #1  

#4 TI="breast fed" or TI="breast feeding" or TI="breast feed"  

#3 TI=breast-fe*  

#2 TI=breastfe*  

#1 Topic=(breastfeeding)

CINAHL (1 January 2006 to 14 June 2011)

1. exp BREAST FEEDING/

2. ((breastfe* OR breast-fe*) AND (exclusive* OR alone OR only)).ti,ab

3. exclusive*.ti,ab

4. 1 AND 3

5. 2 OR 4

African Index Medicus (searched 15 June 2011)

(breastfeeding or breastfed or breastfeed or breast-fed or breast-feeding or breast-feed or "breast feed" or "breast fed" or "breast feeding" [Key Word]) and (exclusive or exclusively or exclusiveness or alone or only [Key Word] )

IMEMR (searched 15 June 2011)

(breastfeeding or breastfed or breastfeed or breast-fed or breast-feeding or breast-feed or "breast feed" or "breast fed" or "breast feeding") and (exclusive or exclusively or exclusiveness or alone or only)

LILACS (searched 15 June 2011)

(breastfeeding or breastfed or breastfeed or breastfeeding or breast-fed or breast-feeding or breast-feed or "breast feed" or "breast fed" or "breast feeding" or lactancia) and (exclusive or exclusively or exclusiveness or alone or only or exclusiva or exclusivo)

What's new

Last assessed as up-to-date: 17 June 2011.

DateEventDescription
14 June 2011New citation required but conclusions have not changedNew evidence from the Belarusian study (Kramer 2000a) suggests that six months of exclusive breastfeeding confers no benefit (versus three months of exclusive breastfeeding followed by continued partial breastfeeding through six months) on height, weight, body mass index, dental caries, cognitive ability, or behaviour at 6.5 years of age. The overall conclusions have not changed.
14 June 2011New search has been performed

Search updated.

One new study included (Duijts 2010) and an additional report of Kramer 2000a identified.  Five new excluded studies (Chantry 2007; Evelein 2011; Meinzen-Derr 2006; Rebhan 2009; Weyermann 2006).

History

Protocol first published: Issue 1, 2002
Review first published: Issue 1, 2002

DateEventDescription
20 September 2008AmendedConverted to new review format.
22 May 2007New search has been performedSearch updated December 2006. We identified five new trials; two have been included (Khadivzadeh 2004; Onayade 2004) and three have been excluded (Chantry 2006; Ly 2006; Wang 2005). The conclusions of the review have not changed.

Contributions of authors

Ritsuko Kakuma: carried out the initial screening of all citations located in the literature search, independently rated each study for quality, independently extracted the data and entered them into Review Manager, and reviewed the drafts for accuracy.

Mike Kramer: planned the review, made the final selection of included studies, independently rated the study quality and extracted the data into Review Manager, and prepared the text.

Declarations of interest

Dr Kramer is the principal investigator of one of the studies (Kramer 2000a) included in this review.

Sources of support

Internal sources

  • McGill University, Canada.

External sources

  • Canadian Institutes of Health Research, Canada.

  • Canadian Cochrane Network, Canada.

  • Department of Nutrition for Health and Development, WHO, Switzerland.

Notes

This review has been processed through the Cochrane Pregnancy and Childbirth Group although its subject matter falls outside the scope of the Group. The Group's scope does include the initiation of breastfeeding, but not the timing of its cessation. However, the topic is clearly of global importance and because it did not readily fit within the scope of any Cochrane review group, the Pregnancy and Childbirth Group was happy to assist with publication. This review was based on a systematic review by M Kramer, that was commissioned by the World Health Organization (WHO). The WHO review was very extensively peer reviewed by experts in review methodology and statistics, and in infant nutrition and lactation, including experts that the Review Group would have approached for our own refereeing purposes. We have therefore not sought an initial protocol, nor subjected the Cochrane review to further peer review of this type. The review has, however, been reviewed by the Consumer Panel of the Pregnancy and Childbirth Group.

There are other unusual features of this review:

  1. Its title does not fit with the standard Cochrane format but we have been unable to construct a satisfactory title that does, whilst doing justice to the scope of the topic.

  2. It includes data from studies in addition to randomized trials.

  3. Maintenance and updating will be the sole responsibility of the contact author as the search strategy of our Review Group does not extend to this topic.

Jim Neilson
Co-ordinating Editor
Cochrane Pregnancy and Childbirth Group

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Adair 1993a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: A.
Follow-up: A.
Blinding: A for weight, B for length.
Participants1204 Filipino infants.
InterventionsEBF = little or no nutritive foods or fluids other than BF for 6 months (n = 370).
MBF = BF with introduction of nutritive foods or liquids at 4 months (n = 834).
OutcomesWeight and length gain 4-6 months.
NotesMultivariate analysis did not affect outcome comparison, but data not presented.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Ahn 1980

MethodsDesign: retrospective cohort.
Quality assessment
Control for confounding: B.
Follow-up: C.
Blinding: A for weight, B for length.
Participants96 healthy U.S. infants living in Baltimore-Washington area who were EBF for at least 6 months.
InterventionsEBF = BF with no solids or liquids other than human milk for > 6 months (n = 50).
MBF = EBF for <= 6 months, then MBF until > 6 months (n = 46).
OutcomesWeight and length gain in first 12 months.
Notes1. No quantitative data provided.
2. Data requested on weight and length gain and illnesses in first year.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Akeson 1996a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight and blood analyses, B for length.
Participants44 healthy Swedish infants EBF for the first 3 months.
InterventionsEBF = BF + < 125 ml/day of formula for >= 6 months (n = 26).
MBF = EBF for >= 3 months, then BF >= 2 times/day + > 125 ml/day of formula for >= 6 months (n = 18).
OutcomesWeight and length gain 4-8 months, 6-9, and 8-12 months; total and essential amino acid concentrations at 6 months.
Notes1. N's in tables not provided for weight and length.
2. Identical data for length gain for the 2 groups at 8-12 months: misprint?
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Brown 1991a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: B.
Follow-up: C.
Blinding: A for weight, B for length.
Participants36 poor, peri-urban Peruvian infants.
InterventionsEBF = little or no nutritive foods or fluids other than BF for 6 months (n = 15).
MBF = BF with introduction of nutritive foods and fluids at 4 months (n = 21).
OutcomesWeight and length gain 4-6 months.
NotesMultivariate analysis did not affect outcome comparison, but data not presented.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Castillo 1996

MethodsDesign: cross-sectional.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight, B for length.
Participants1122 Chilean children 3.0-5.9 months of age.
InterventionsEBF = BF only (unclear if water, juices, or other liquids permitted) (n = 974).
MBF = EBF for >= 2.9 months, then BF + solid food (n = 148).
OutcomesLow WAZ, LAZ, high WLZ.
Notes1. Cannot use data quantitatively, because prevalences, confidence intervals, and SEs not provided.
2. Low WAZ and LAZ defined as <- 1, high WLZ as >+ 1.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Cohen 1994a

MethodsDesign: controlled trial.
Quality assessment
Randomization: C.
Follow-up: C.
Blinding: A for weight and maternal postpartum weight loss, B for length, developmental milestones, and lactational amenorrhea.
Jadad scale
Randomization: 0/2.
Double-blinding: 0/2.
Withdrawals: 1/1.
Total Jadad scale score: 1/5.
Participants141 Honduran infants of low-income families with poor sanitation.
InterventionsEBF = BF with no other liquids or solids until 6 months (n = 50).
MBF = introduction of complementary solid food at 4 months with either ad libitum nursing (SF) or maintenance of baseline nursing frequency (SF-M) (n = 91).
OutcomesWeight and length gain 4-6 and 6-12 months; WAZ, LAZ, and WLZ at 6 months; receipt of Fe supplements 6-9 months; hemoglobin and ferritin at 6 months; % of days with fever, cough, nasal congestion, nasal discharge, hoarseness, and diarrhea; age first crawled, age first sat from lying position, walking by 12 months; maternal postpartum weight loss 4-6 months; resumption of menses by 6 months.
Notes1. Nonrandom allocation.
2. Cluster allocation by week of birth, while analyses done at individual level.
3. Analysis not based on intention to treat.
4. SF-M and SF groups combined as MBF group.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)High riskC - Inadequate

Dewey 1999a

MethodsDesign: controlled trial.
Quality assessment
Randomization: B.
Follow-up: C.
Blinding: A for weight, B for length.
Jadad scale
Randomization: 1/2.
Double-blinding: 0/2.
Withdrawals: 1/1.
Total Jadad scale score: 2/5.
Participants119 LBW Honduran term infants.
InterventionsEBF = BF with no other liquids or solids until 6 months (n = 59).
MBF = introduction of complementary solid food at 4 months with maintenance of baseline nursing frequency (n = 60).
OutcomesWeight and length gain 4-6 and 6-12 months; WAZ, LAZ, and WLZ at 6 months; plasma zinc concentration at 6 months;
% of days with fever, cough, nasal congestion, nasal discharge, hoarseness, and diarrhea; age first crawled, age first sat from lying position, walking by 12 months; maternal postpartum weight loss 4-6 months; resumption of menses by 6 months.
Notes1. Cluster-randomized by week of birth, while analyses done at individual level.
2. Analysis not based on intention to treat.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Low riskA - Adequate

Duijts 2010

MethodsProspective, population-based pregnancy/birth cohort study (Generation R Study from Rotterdam.)
Participants1095 healthy Dutch singleton infants.
Interventions

EBF = BF without other milk or solids until 6 months (n = 58).

MBF = introduction of milk and/or solids between 4 and 6 months with continuation of partial BF until 6 months (n = 1037).

Outcomes1 or more episodes of upper respiratory tract, lower respiratory tract, and gastrointestinal tract infection in first 6 months and from 7-12 months.
Notes

1. Outcomes based on mailed questionnaires (maternal report) sent at 6 and 12 months postpartum.

2. Of 7893 total infants enrolled in the cohort, breastfeeding, outcome, and covariate (potential confounder) data were available in only ˜3500 (44%) at 6 months and ˜3000 (38%) at 12 months.

Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not done

Duncan 1993

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: A.
Follow-up: B.
Blinding: B.
Participants279 healthy U.S. infants.
InterventionsEBF = EBF for >= 6 months (n = 138).
MBF = EBF for 4 months with introduction of formula or solid foods between 4 and 6 months (n = 141).
OutcomesNumber of episodes of OM, 1 or more episodes of OM, and frequent OM in first 12 months.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Heinig 1993

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight, B for length and sleeping time.
Participants60 healthy U.S. infants living in Davis, CA.
InterventionsEBF = BF ± <= 120 ml/day of other milk or formula for >= 12 months and no solids < 6 months (n = 19).
MBF = BF ± <= 120 ml/day of other milk or formula for >= 12 months; solids introduced at 4-6 months (n = 41).
OutcomesMonthly weight and length gain at 6-9 and 9-12 months; total sleeping time at 9 months.
Notes1. Data on weight and length gain 4-6 months included in pooled analysis of WHO 1994.
2. No quantitative data presented on morbidity.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Huffman 1987

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: B.
Blinding: A.
Participants1018 Bangladeshi women with live births.
InterventionsEBF = BF with no other liquids or solids for >= 7 months (n = 647).
MBF = EBF for 4 months with introduction of liquid or solid supplements before 7 months (n = 371).
OutcomesDuration of lactational amenorrhea.
Notes1. Over 95% of study women BF > 16 months, so all MBF women assumed to continue BF >= 6 months.
2. Multivariate (Cox) regression controlled for maternal education, parity, religion, and weight, but reference group EBF < 1 month.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Kajosaari 1983

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: B.
Follow-up: C.
Blinding: C.
Participants135 healthy Finnish infants of atopic parents.
InterventionsEBF = BF without cow milk-based formula; occasional water permitted; solids introduced at about 6 months (n = 70).
MBF = BF with introduction of solids at about 3 months (n = 65).
OutcomesAtopic eczema and food allergy at 1 year; any atopy, atopic eczema, pollen allergy, asthma, food allergy, and allergy to animal dander at 5 years.
NotesDiscrepancy between 1- and 5-year follow-up reports regarding sample sizes per group (inverted from 1 report to the other).
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Khadivzadeh 2004

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: A.
Follow-up: A.
Blinding: A for weight, B for morbidity measures.
Participants193 healthy, term Iranian infants followed at 1 of 5 randomly urban health centres.
InterventionsEBF = no other liquid or solid before 6 months (n = 98).
MBF = EBF for 4 months, then complementary foods.
OutcomesWeight and length gains; incidence of respiratory and gastrointestinal infection during the period of 4 to 6 months.
Notes1. EBF and MBF infants 'matched' for sex and for weight and length at 4 months, but matching criteria for weight and length not provided.
2. 2 EBF and 5 MBF infants excluded for "noncompliance" with self-selected group assignment.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Khan 1984

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight, B for length.
Participants48 rural Bangladeshi children.
InterventionsEBF = no other liquid or semi-solid food (water permitted) and introduction of supplementation between 12 and 15 months.
MBF = BF + introduction of supplements between 6 and 15 months.
OutcomesWeight and length through 24 months; number of diarrheal episodes; average duration of diarrhea.
Notes1. Graphical presentation of data only without SDs, thus precluding quantitative reporting.
2. Misprint in legend for Figure 2.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Kramer 2000a

MethodsDesign: prospective cohort nested within randomized trial.
Quality assessment
Control for confounding: A.
Follow-up: A.
Blinding: A for weight, B for length and head circumference.
Participants3483 healthy, term Belarussian infants.
InterventionsEBF = no liquids or solids other than breast milk for >= 6 months (n = 621).
MBF = EBF for 3 months with introduction of nonbreast milk liquids or solids, or both, by 6 months (n = 2862).
OutcomesMonthly weight and length gain 3-6, 6-9, and 9-12 months; WAZ, LAZ, WLZ, and head circumference at 6, 9, and 12 months; death; occurrence of and hospitalization for gastrointestinal and respiratory infection; atopic eczema and recurrent wheezing in first 12 months; height, weight, adiposity, allergy symptoms and diagnoses, skin-prick tests, dental caries, IQ, teacher's academic ratings, and parent's and teacher's assessments of behaviour at 6.5 years.
NotesOutcomes analyzed using multilevel regression accounting for clustering and controlling for geographic region, urban vs rural location, parental education, family atopic history, and maternal smoking during pregnancy.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Oddy 1999

MethodsDesign: prospective cohort within randomized trial.
Quality assessment
Control for confounding: C.
Follow-up: A for 1-year outcomes, B for asthma at 6 years, C for skin-prick tests at 6 years.
Blinding: B.
Participants510 Australian infants.
InterventionsEBF = no nonbreast milk or solids for >= 6 months (n = 246).
MBF = EBF for 4 months, with introduction of nonbreast milk or solids, or both, at 4-6 months (n = 264).
OutcomesOccurrence of and hospitalization for upper and lower respiratory tract infection and recurrent wheezing in first 12 months; asthma and skin-prick tests at 6 years.
Notes1. Published article includes multivariate control for confounders, but data included here are raw and unpublished.
2. Current asthma at 6 years defined as doctor-diagnosed + wheeze in previous year without a cold + receipt of asthma medication.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Onayade 2004

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: A for illness episodes, C for weight.
Blinding: A for weight, B for morbidity measures.
Participants309 healthy, term infants born in Nigerian urban university teaching hospital.
InterventionsEBF = no other liquid or solid for >= 6 months (n = 264).
MBF = EBF for 4 to < 6 months, then water, formula, or cereal (n = 45).
OutcomesRespiratory infection, gastrointestinal infection, weight, and length.
Notes1. Only 34 of 45 MBF infants had recorded weights an lengths.
2. Error in Table 4: recorded n = 266 (vs 264 total) EBF infants with recorded weight and length.
3. No control for apparent (but small) sociodemographic differences between groups.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Pisacane 1995

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A.
Participants30 term, appropriate-for-gestational-age Italian infants recruited at 6 months and BF for first year of life.
InterventionsEBF = BF only without any other fluids or solids for >= 7 months (n = 9).
MBF = EBF for 4-6 months with other foods introduced before 7 months (n = 21).
OutcomesHemoglobin and serum ferritin concentrations at 12 months.
Notes 
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Rao 1992

MethodsDesign: cross-sectional.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight, B for length.
Participants31 poor East Indian children < 3 years living under poor hygienic conditions.
InterventionsEBF = no supplementation with other milk or traditional solid foods for 6-12 months (n = 11).
MBF = EBF for 6 months, then supplementation with other milk or traditional foods from 6-12 months (n = 20).
OutcomesWeight-for-age < 75% of reference mean.
Notes1. Study population included all children < 3 years living in 3 villages.
2. Data extracted for males only, because large proportion of females not initially EBF for >= 6 months.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Savilahti 1987a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A.
Participants26 healthy Finnish infants.
InterventionsEBF = BF without supplementary formula or solid foods for 9 months (n = 7).
MBF = BF with introduction of solids at 6 months (n = 19).
OutcomesVLDL, LDL, HDL2, HDL3, apoprotein B, and total triglyceride concentration at 9 months.
NotesAtopic outcomes not compared in EBF vs MBF groups as defined here.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Simondon 1997a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: A for monthly weight and length gain 4-6 months, C for other outcomes.
Follow-up: B.
Blinding: A for weight and length.
Participants370 Senegalese infants recruited at 2-3 months.
InterventionsEBF = breast milk and water only until at least 6-7 months (n = 154).
MBF = breast milk, water, and introduction of complementary food between 4 and 7 months of age (n = 216).
OutcomesMonthly weight and length gain 4-6 and 6-9 months; WAZ, LAZ, WLZ, and mid-upper arm circumference at 4-5, 6-7, and 9-10 months; duration of lactational amenorrhea.
Notes1. EBF = 'very late' group, MBF = 'early' and 'late' groups combined.
2. Monthly weight and length gains 4-6 months based on multivariate control for maternal size and education and z-score at 2-3 months.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

WHO 1994a

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: C.
Follow-up: C.
Blinding: A for weight, B for length.
ParticipantsPooled sample of healthy developed-country infants (n = 358).
InterventionsEBF = BF ± other liquids for >= 6 months (n = 200).
MBF = BF ± other liquids for >= 4 months with other milk ± solids introduced between 4 and 6 months (n = 158).
OutcomesMonthly weight and length gain 4-6 months.
NotesMultivariate control for initial weight and length, but data not presented.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

WHO 1997

  1. a

    BF: breastfeeding
    EBF: exclusive breastfeeding
    HDL2: high-density lipoprotein-2
    HDL3: high-density lipoprotein-3
    LAZ: length-for-age z-score
    LBW: low birthweight
    LDL: low density lipoprotein
    MBF: mixed breastfeeding
    OM: otitis media
    SD: standard deviation
    SE: standard error
    SES: socioeconomic status
    VLDL: very low density lipoprotein
    vs: versus
    WAZ: weight-for-age z-score
    WLZ: weight-for-length z-score

MethodsDesign: prospective cohort.
Quality assessment
Control for confounding: A.
Follow-up: C.
Blinding: A for weight, B for length.
ParticipantsPooled sample of mid-to high-SES infants from 2 developed and 3 developing countries (n = 556).
InterventionsEBF = BF ± noncaloric liquids for >= 6 months (n = 179).
MBF = BF ± caloric liquids or solids introduced at 4-6 months (n = 377).
OutcomesMonthly weight and length gain 4-8 months.
Notes1. Multilevel regression used to control for maternal size and education and infant size and growth < 4 months.
2. Large losses to follow-up; retained sample 'similar' to full sample, but details not provided.
Risk of bias
BiasAuthors' judgementSupport for judgement
Allocation concealment (selection bias)Unclear riskD - Not used

Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion
Chantry 2006The group with full breastfeeding from 4 to < 6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Chantry 2007The group with full breastfeeding from 4 to < 6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Evelein 2011The group with exclusive breastfeeding from 3-6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Ly 2006Both intervention and control groups were free to consume locally available complementary foods prior to 4 months and during the intervention period from 4 to 7 months.
Meinzen-Derr 2006The group with exclusive breastfeeding from 4-6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Rebhan 2009The group with full/exclusive breastfeeding from 4-6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Wang 2005Those infants in the control group (mixed breastfeeding at ages 4-6 months) were not necessarily exclusively breastfed until 4 months.
Weyermann 2006Comparing the 533 total (207+326) infants who were breastfed to any extent for at least 6 months with the 599 (277+322) who were exclusively breastfed for at least 3 months, it appears as if 66 (599-533) of the 277 infants listed as exclusively breastfed for 3-< 6 months discontinued breastfeeding before 6 months (see Table 1),

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