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Optimal duration of exclusive breastfeeding

  1. Michael S Kramer1,*,
  2. Ritsuko Kakuma2

Editorial Group: Cochrane Pregnancy and Childbirth Group

Published Online: 15 AUG 2012

Assessed as up-to-date: 17 JUN 2011

DOI: 10.1002/14651858.CD003517.pub2


How to Cite

Kramer MS, Kakuma R. Optimal duration of exclusive breastfeeding. Cochrane Database of Systematic Reviews 2012, Issue 8. Art. No.: CD003517. DOI: 10.1002/14651858.CD003517.pub2.

Author Information

  1. 1

    McGill University Faculty of Medicine, Departments of Pediatrics and Epidemiology, Biostatistics and Occupational Health, Montreal, Quebec, Canada

  2. 2

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

*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.

Publication History

  1. Publication Status: New search for studies and content updated (no change to conclusions)
  2. Published Online: 15 AUG 2012

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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.


InterventionsEBF = 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.


Notes1. 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

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),

 
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]

 
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]

 
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]

 
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]

 
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]