Optimal duration of exclusive breastfeeding

 

Characteristics of included studies [ordered by study ID]

Adair 1993a

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Methods	Design: prospective cohort. Quality assessment Control for confounding: A. Follow up: A. Blinding: A for weight, B for length.
Participants	1204 Filipino infants.
Interventions	EBF = 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).
Outcomes	Weight and length gain 4-6 months.
Notes	Multivariate analysis did not affect outcome comparison, but data not presented.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Ahn 1980

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Methods	Design: retrospective cohort. Quality assessment Control for confounding: B. Follow up: C. Blinding: A for weight, B for length.
Participants	96 healthy U.S. infants living in Baltimore-Washington area who were EBF for at least 6 months.
Interventions	EBF = 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).
Outcomes	Weight and length gain in first 12 months.
Notes	1. No quantitative data provided. 2. Data requested on weight and length gain and illnesses in first year.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Akeson 1996a

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight and blood analyses, B for length.
Participants	44 healthy Swedish infants EBF for the first 3 months.
Interventions	EBF = 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).
Outcomes	Weight and length gain 4-8 months, 6-9, and 8-12 months; total and essential amino acid concentrations at 6 months.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Brown 1991a

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Methods	Design: prospective cohort. Quality assessment Control for confounding: B. Follow up: C. Blinding: A for weight, B for length.
Participants	36 poor, peri-urban Peruvian infants.
Interventions	EBF = 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).
Outcomes	Weight and length gain 4-6 months.
Notes	Multivariate analysis did not affect outcome comparison, but data not presented.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Castillo 1996

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Methods	Design: cross-sectional. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight, B for length.
Participants	1122 Chilean children 3.0-5.9 months of age.
Interventions	EBF = BF only (unclear if water, juices, or other liquids permitted) (n = 974). MBF = EBF for >= 2.9 months, then BF + solid food (n = 148).
Outcomes	Low WAZ, LAZ, high WLZ.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Cohen 1994a

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Methods	Design: 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.
Participants	141 Honduran infants of low-income families with poor sanitation.
Interventions	EBF = 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).
Outcomes	Weight 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.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	No	C - Inadequate

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Dewey 1999a

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Methods	Design: 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.
Participants	119 LBW Honduran term infants.
Interventions	EBF = 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).
Outcomes	Weight 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.
Notes	1. Cluster randomized by week of birth, while analyses done at individual level. 2. Analysis not based on intention to treat.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Yes	A - Adequate

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Duncan 1993

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Methods	Design: prospective cohort. Quality assessment Control for confounding: A. Follow up: B. Blinding: B.
Participants	279 healthy U.S. infants.
Interventions	EBF = 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).
Outcomes	Number of episodes of OM, one or more episodes of OM, and frequent OM in first 12 months.
Notes
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Heinig 1993

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight, B for length and sleeping time.
Participants	60 healthy U.S. infants living in Davis, CA.
Interventions	EBF = 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).
Outcomes	Monthly weight and length gain at 6-9 and 9-12 months; total sleeping time at 9 months.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Huffman 1987

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: B. Blinding: A.
Participants	1018 Bangladeshi women with live births.
Interventions	EBF = 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).
Outcomes	Duration of lactational amenorrhea.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Kajosaari 1983

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Methods	Design: prospective cohort. Quality assessment Control for confounding: B. Follow up: C. Blinding: C.
Participants	135 healthy Finnish infants of atopic parents.
Interventions	EBF = 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)
Outcomes	Atopic eczema and food allergy at 1 year; any atopy, atopic eczema, pollen allergy, asthma, food allergy, and allergy to animal dander at 5 years.
Notes	Discrepancy between 1- and 5-year follow-up reports regarding sample sizes per group (inverted from 1 report to the other).
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Khadivzadeh 2004

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Methods	Design: prospective cohort. Quality assessment Control for confounding: A. Follow up: A. Blinding: A for weight, B for morbidity measures.
Participants	193 healthy, term Iranian infants followed at 1 of 5 randomly urban health centres.
Interventions	EBF = no other liquid or solid before 6 months (n = 98). MBF = EBF for 4 months, then complementary foods.
Outcomes	Weight and length gains; incidence of respiratory and gastrointestinal infection during the period of 4 to 6 months.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Khan 1984

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight, B for length.
Participants	48 rural Bangladeshi children.
Interventions	EBF = 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.
Outcomes	Weight and length through 24 months; number of diarrheal episodes; average duration of diarrhea.
Notes	1. Graphical presentation of data only without SDs, thus precluding quantitative reporting. 2. Misprint in legend for Figure 2.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Kramer 2000a

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Methods	Design: 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.
Participants	3483 healthy, term Belarussian infants.
Interventions	EBF = 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).
Outcomes	Monthly 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.
Notes	Growth outcomes analyzed using multilevel regression controlling for geographic region, urban vs rural location, maternal education, and size or growth <= 3 months.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Oddy 1999

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Methods	Design: 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.
Participants	510 Australian infants.
Interventions	EBF = 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).
Outcomes	Occurrence 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.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Onayade 2004

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Methods	Design: 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.
Participants	309 healthy, term infants born in Nigerian urban university teaching hospital.
Interventions	EBF = no other liquid or solid for >= 6 months (n = 264). MBF = EBF for 4 to < 6 months, then water, formula, or cereal (n = 45).
Outcomes	Respiratory infection, gastrointestinal infection, weight, and length.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Pisacane 1995

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A.
Participants	30 term, appropriate-for-gestational-age Italian infants recruited at 6 months and BF for first year of life.
Interventions	EBF = 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).
Outcomes	Hemoglobin and serum ferritin concentrations at 12 months.
Notes
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Rao 1992

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Methods	Design: cross-sectional. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight, B for length.
Participants	31 poor East Indian children < 3 years living under poor hygienic conditions.
Interventions	EBF = 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).
Outcomes	Weight-for-age < 75% of reference mean.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Savilahti 1987a

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A.
Participants	26 healthy Finnish infants.
Interventions	EBF = BF without supplementary formula or solid foods for 9 months (n = 7). MBF = BF with introduction of solids at 6 months (n = 19).
Outcomes	VLDL, LDL, HDL2, HDL3, apoprotein B, and total triglyceride concentration at 9 months.
Notes	Atopic outcomes not compared in EBF vs MBF groups as defined here.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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Simondon 1997a

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Methods	Design: 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.
Participants	370 Senegalese infants recruited at 2-3 months.
Interventions	EBF = 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).
Outcomes	Monthly 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.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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WHO 1994a

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Methods	Design: prospective cohort. Quality assessment Control for confounding: C. Follow up: C. Blinding: A for weight, B for length.
Participants	Pooled sample of healthy developed-country infants (n = 358).
Interventions	EBF = 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).
Outcomes	Monthly weight and length gain 4-6 months.
Notes	Multivariate control for initial weight and length, but data not presented.
Risk of bias
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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WHO 1997

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Methods	Design: prospective cohort. Quality assessment Control for confounding: A. Follow up: C. Blinding: A for weight, B for length.
Participants	Pooled sample of mid-to high-SES infants from 2 developed and 3 developing countries (n = 556).
Interventions	EBF = BF ± noncaloric liquids for >= 6 months (n = 179). MBF = BF ± caloric liquids or solids introduced at 4-6 months (n = 377).
Outcomes	Monthly weight and length gain 4-8 months.
Notes	1. 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
Item	Authors' judgement	Description
Allocation concealment?	Unclear	D - Not used

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 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

 

Characteristics of excluded studies [ordered by study ID]

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Study	Reason for exclusion
Chantry 2006	The group with full breastfeeding from 4 to < 6 months did not necessarily continue mixed (partial) breastfeeding to at least 6 months.
Ly 2006	Both 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.
Wang 2005	Those infants in the control group (mixed breastfeeding at ages 4-6 months) were not necesarily exclusively breastfed until 4 months.

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Comparison 1. Exclusive versus mixed breastfeeding 4-6 months, developing countries, controlled trials

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Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Monthly weight gain from 4-6 months (g/mo)	2	265	Mean Difference (IV, Fixed, 95% CI)	20.78 [-21.99, 63.54]
2 Monthly weight gain from 6-12 months (g/mo)	2	233	Mean Difference (IV, Fixed, 95% CI)	-2.62 [-25.85, 20.62]
3 Monthly length gain 4-6 months (cm/mo)	2	265	Mean Difference (IV, Fixed, 95% CI)	0.10 [-0.04, 0.24]
4 Monthly length gain 6-12 months (cm/mo)	2	233	Mean Difference (IV, Fixed, 95% CI)	-0.04 [-0.10, 0.02]
5 Weight-for-age z-score at 6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.18 [-0.06, 0.41]
6 Length-for-age z-score at 6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.11 [-0.11, 0.33]
7 Weight-for-length z-score at 6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.09 [-0.13, 0.31]
8 Weight-for-age z-score < -2 at 6 months	2	260	Risk Ratio (M-H, Fixed, 95% CI)	2.14 [0.74, 6.24]
9 Length-for-age z-score < -2 at 6 months	2	260	Risk Ratio (M-H, Fixed, 95% CI)	1.18 [0.56, 2.50]
10 Weight-for-length z-score < -2 at 6 months	2	260	Risk Ratio (M-H, Fixed, 95% CI)	1.38 [0.17, 10.98]
11 Receipt of Fe supplements 6-9 months	1	139	Risk Ratio (M-H, Fixed, 95% CI)	1.20 [0.91, 1.58]
12 Hemoglobin concentration (g/L) at 6 months	1	139	Mean Difference (IV, Fixed, 95% CI)	-5.0 [-8.46, -1.54]
13 Hemoglobin concentration < 110 g/L at 6 months	1	139	Risk Ratio (M-H, Fixed, 95% CI)	1.20 [0.91, 1.58]
14 Hemoglobin concentration < 103 g/L at 6 months	1	139	Risk Ratio (M-H, Fixed, 95% CI)	1.29 [0.75, 2.23]
15 Hematocrit (%) at 6 months	1	139	Mean Difference (IV, Fixed, 95% CI)	-1.20 [-2.15, -0.25]
16 Hematocrit < 33% at 6 months	1	139	Risk Ratio (M-H, Fixed, 95% CI)	1.50 [0.85, 2.64]
17 Plasma ferritin concentration (mcg/L) at 6 months	1	135	Mean Difference (IV, Fixed, 95% CI)	-18.9 [-37.31, -0.49]
18 Plasma ferritin concentration < 12 mcg/L at 6 months	1	135	Risk Ratio (M-H, Fixed, 95% CI)	2.34 [0.86, 6.35]
19 Plasma ferritin concentration < 15 mcg/L at 6 months	1	135	Risk Ratio (M-H, Fixed, 95% CI)	2.93 [1.13, 7.56]
20 Plasma zinc concentration < 70 mcg/dL at 6 months	1	101	Risk Ratio (M-H, Fixed, 95% CI)	0.75 [0.43, 1.33]
21 % of days with fever 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.26 [-1.29, 1.81]
22 % of days with cough 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	2.83 [-2.22, 7.87]
23 % of days with nasal congestion 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.11 [-4.41, 4.63]
24 % of days with nasal discharge 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	0.26 [-2.60, 3.12]
25 % of days with hoarseness 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	-0.19 [-1.17, 0.79]
26 % of days with diarrhea 4-6 months	2	260	Mean Difference (IV, Fixed, 95% CI)	1.15 [-0.35, 2.65]
27 % of days with fever 6-12 months	2	258	Mean Difference (IV, Fixed, 95% CI)	-0.39 [-2.80, 2.02]
28 % of days with nasal congestion 6-12 months	2	258	Mean Difference (IV, Fixed, 95% CI)	3.11 [-0.12, 6.35]
29 % of days with diarrhea 6-12 months	2	258	Mean Difference (IV, Fixed, 95% CI)	-0.74 [-2.34, 0.86]
30 Age first crawled (mo)	2	240	Mean Difference (IV, Fixed, 95% CI)	-0.80 [-1.26, -0.34]
31 Age first sat from lying position (mo)	2	238	Mean Difference (IV, Fixed, 95% CI)	-0.17 [-0.56, 0.21]
32 Did not walk by 12 months	2	233	Risk Ratio (M-H, Fixed, 95% CI)	0.89 [0.72, 1.09]
33 Maternal postpartum weight loss 4-6 months (kg)	2	260	Mean Difference (IV, Fixed, 95% CI)	0.42 [0.02, 0.82]
34 Maternal resumption of menses 6 months postpartum	2	189	Risk Ratio (M-H, Fixed, 95% CI)	0.58 [0.33, 1.03]

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Comparison 2. Exclusive versus mixed breastfeeding 3-7 months, developing countries, observational studies

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Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Monthly weight gain 4-6 months (g/mo)	4	1803	Mean Difference (IV, Fixed, 95% CI)	-10.10 [-27.68, 7.48]
2 Monthly weight gain 6-9 months (g/mo)	1	319	Mean Difference (IV, Fixed, 95% CI)	-6.0 [-54.15, 42.15]
3 Monthly length gain 4-6 months (cm/mo)	4	1803	Mean Difference (IV, Fixed, 95% CI)	0.04 [-0.02, 0.11]
4 Monthly length gain 6-9 months (cm/mo)	1	319	Mean Difference (IV, Fixed, 95% CI)	0.04 [-0.06, 0.14]
5 Weight-for-age z-score at 6-7 months	1	370	Mean Difference (IV, Fixed, 95% CI)	0.13 [-0.09, 0.35]
6 Weight-for-age z-score at 9-10 months	1	319	Mean Difference (IV, Fixed, 95% CI)	0.09 [-0.15, 0.33]
7 Length-for-age z-score at 6-7 months	1	370	Mean Difference (IV, Fixed, 95% CI)	0.04 [-0.14, 0.22]
8 Length-for-age z-score at 9-10 months	1	319	Mean Difference (IV, Fixed, 95% CI)	0.11 [-0.09, 0.31]
9 Weight-for-length z-score at 6-7 months	1	370	Mean Difference (IV, Fixed, 95% CI)	0.11 [-0.09, 0.31]
10 Weight-for-length z-score at 9-10 months	1	319	Mean Difference (IV, Fixed, 95% CI)	0.01 [-0.21, 0.23]
11 Weight-for-age z-score < -2 at 6-7 months	1	370	Risk Ratio (M-H, Fixed, 95% CI)	0.92 [0.54, 1.58]
12 Weight-for-age z-score < -2 at 9-10 months	1	319	Risk Ratio (M-H, Fixed, 95% CI)	0.93 [0.64, 1.36]
13 Length-for-age z-score < -2 at 6-7 months	1	370	Risk Ratio (M-H, Fixed, 95% CI)	1.20 [0.57, 2.53]
14 Length-for-age z-score < -2 at 9-10 months	1	319	Risk Ratio (M-H, Fixed, 95% CI)	1.21 [0.62, 2.37]
15 Weight-for-length z-score < -2 at 6-7 months	1	370	Risk Ratio (M-H, Fixed, 95% CI)	0.42 [0.12, 1.50]
16 Weight-for-length z-score < -2 at 9-10 months	1	319	Risk Ratio (M-H, Fixed, 95% CI)	0.82 [0.39, 1.71]
17 Mid-upper arm circumference at 6-7 months (cm)	1	370	Mean Difference (IV, Fixed, 95% CI)	0.20 [-0.04, 0.44]
18 Mid-upper arm circumference at 9-10 months (cm)	1	319	Mean Difference (IV, Fixed, 95% CI)	0.10 [-0.16, 0.36]
19 One or more episodes of gastrointestinal infection at 4-6 months	1	193	Risk Ratio (M-H, Fixed, 95% CI)	0.41 [0.21, 0.78]
20 One or more episodes of respiratory infection at 4-6 months	1	193	Risk Ratio (M-H, Fixed, 95% CI)	0.68 [0.43, 1.06]
21 Resumption of menses by 6-7 months postpartum	1	686	Risk Ratio (M-H, Fixed, 95% CI)	0.19 [0.05, 0.79]

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Comparison 3. Prolonged (> 6 months) exclusive versus mixed breastfeeding, developing countries, observational studies

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Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Weight-for-age < 75% of reference mean	1	31	Risk Ratio (M-H, Fixed, 95% CI)	0.61 [0.26, 1.43]

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Comparison 4. Exclusive versus mixed breastfeeding 3-7 months, developed countries, observational studies

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Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Monthly weight gain 3-8 months (g/mo)	4	4388	Mean Difference (IV, Fixed, 95% CI)	-12.45 [-23.46, -1.44]
2 Monthly weight gain 6-9 months (g/mo)	2	3432	Mean Difference (IV, Fixed, 95% CI)	-2.26 [-16.94, 12.42]
3 Monthly weight gain 8-12 months (g/mo)	3	3450	Mean Difference (IV, Fixed, 95% CI)	-1.82 [-16.72, 13.08]
4 Monthly length gain 3-8 months (cm/mo)	4	4385	Mean Difference (IV, Fixed, 95% CI)	Not estimable
5 Monthly length gain 6-9 months (cm/mo)	2	3430	Mean Difference (IV, Fixed, 95% CI)	-0.04 [-0.10, 0.01]
6 Monthly length gain 8-12 months (cm/mo)	3	3448	Mean Difference (IV, Fixed, 95% CI)	0.09 [0.03, 0.14]
7 Weight-for-age z-score at 6 months	1	3455	Mean Difference (IV, Fixed, 95% CI)	-0.09 [-0.16, -0.02]
8 Weight-for-age z-score at 9 months	1	3400	Mean Difference (IV, Fixed, 95% CI)	-0.10 [-0.18, -0.02]
9 Weight-for-age z-score at 12 months	1	3458	Mean Difference (IV, Fixed, 95% CI)	-0.09 [-0.17, -0.01]
10 Length-for-age z-score at 6 months	1	3454	Mean Difference (IV, Fixed, 95% CI)	-0.12 [-0.20, -0.04]
11 Length-for-age z-score at 9 months	1	3398	Mean Difference (IV, Fixed, 95% CI)	-0.14 [-0.22, -0.06]
12 Length-for-age z-score at 12 months	1	3458	Mean Difference (IV, Fixed, 95% CI)	-0.02 [-0.10, 0.06]
13 Weight-for-length z-score at 6 months	1	3454	Mean Difference (IV, Fixed, 95% CI)	0.02 [-0.07, 0.11]
14 Weight-for-length z-score at 9 months	1	3398	Mean Difference (IV, Fixed, 95% CI)	0.03 [-0.06, 0.12]
15 Weight-for-length z-score at 12 months	1	3458	Mean Difference (IV, Fixed, 95% CI)	-0.08 [-0.17, 0.01]
16 Weight-for-age z-score < -2 at 6 months	1	3461	Risk Ratio (M-H, Fixed, 95% CI)	0.92 [0.04, 19.04]
17 Weight-for-age z-score < -2 at 9 months	1	3408	Risk Ratio (M-H, Fixed, 95% CI)	1.52 [0.16, 14.62]
18 Weight-for-age z-score < -2 at 12 months	1	3466	Risk Ratio (M-H, Fixed, 95% CI)	1.15 [0.13, 10.31]
19 Length-for-age z-score < -2 at 6 months	1	3460	Risk Ratio (M-H, Fixed, 95% CI)	1.53 [0.84, 2.78]
20 Length-for-age z-score < -2 at 9 months	1	3406	Risk Ratio (M-H, Fixed, 95% CI)	1.46 [0.80, 2.64]
21 Length-for-age z-score < -2 at 12 months	1	3466	Risk Ratio (M-H, Fixed, 95% CI)	0.66 [0.23, 1.87]
22 Weight-for-length z-score < -2 at 6 months	1	3460	Risk Ratio (M-H, Fixed, 95% CI)	0.31 [0.02, 5.34]
23 Weight-for-length z-score < -2 at 9 months	1	3406	Risk Ratio (M-H, Fixed, 95% CI)	1.14 [0.24, 5.37]
24 Weight-for-length z-score < -2 at 12 months	1	3466	Risk Ratio (M-H, Fixed, 95% CI)	1.15 [0.13, 10.31]
25 Head circumference at 6 months (cm)	1	3440	Mean Difference (IV, Fixed, 95% CI)	-0.10 [-0.23, 0.03]
26 Head circumference at 9 months (cm)	1	3389	Mean Difference (IV, Fixed, 95% CI)	0.07 [-0.06, 0.20]
27 Head circumference at 12 months (cm)	1	3450	Mean Difference (IV, Fixed, 95% CI)	0.19 [0.06, 0.32]
28 Sleeping time at 9 months (min/day)	1	50	Mean Difference (IV, Fixed, 95% CI)	1.0 [-36.65, 38.65]
29 Total essential amino acid concentration (umol/L) at 6 months	1	44	Mean Difference (IV, Fixed, 95% CI)	22.0 [-59.60, 103.60]
30 Total amino acid concentration (umol/L) at 6 months	1	44	Mean Difference (IV, Fixed, 95% CI)	73.0 [-118.22, 264.22]
31 Atopic eczema in first 12 months	2	3618	Risk Ratio (M-H, Fixed, 95% CI)	0.73 [0.49, 1.08]
32 Food allergy at 1 year (by history)	1	135	Risk Ratio (M-H, Fixed, 95% CI)	0.19 [0.08, 0.48]
33 Food allergy at 1 year (by double challenge)	1	135	Risk Ratio (M-H, Fixed, 95% CI)	0.77 [0.25, 2.41]
34 Two or more episodes of wheezing in first 12 months	2	3993	Risk Ratio (M-H, Fixed, 95% CI)	0.79 [0.49, 1.28]
35 Any atopy at 5 years	1	113	Risk Ratio (M-H, Fixed, 95% CI)	0.68 [0.40, 1.17]
36 Atopic eczema at 5 years	1	113	Risk Ratio (M-H, Fixed, 95% CI)	0.97 [0.50, 1.89]
37 Pollen allergy at 5 years	1	113	Risk Ratio (M-H, Fixed, 95% CI)	0.53 [0.28, 1.01]
38 Asthma at 5-6 years	2	552	Risk Ratio (M-H, Fixed, 95% CI)	0.91 [0.61, 1.36]
39 Food allergy at 5 years (by history)	1	113	Risk Ratio (M-H, Fixed, 95% CI)	0.61 [0.12, 3.19]
40 Allergy to animal dander at 5 years	1	113	Risk Ratio (M-H, Fixed, 95% CI)	0.81 [0.24, 2.72]
41 Positive skin prick test at 6 years	1	331	Risk Ratio (M-H, Fixed, 95% CI)	0.99 [0.73, 1.35]
42 Hemoglobin concentration (g/L) at 12 months	1	30	Mean Difference (IV, Fixed, 95% CI)	8.0 [4.03, 11.97]
43 Hemoglobin concentration < 110 g/L at 12 months	1	30	Risk Ratio (M-H, Fixed, 95% CI)	0.12 [0.01, 1.80]
44 Serum ferritin concentration (mcg/L) at 12 months	1	30	Mean Difference (IV, Fixed, 95% CI)	4.70 [-6.30, 15.70]
45 Serum ferritin concetration < 10 mcg/L at 12 months	1	30	Risk Ratio (M-H, Fixed, 95% CI)	0.42 [0.12, 1.54]
46 Death in first 12 months	1	3483	Risk Ratio (M-H, Fixed, 95% CI)	2.30 [0.21, 25.37]
47 One or more episodes of gastrointestinal infection in first 12 months	1	3483	Risk Ratio (M-H, Fixed, 95% CI)	0.67 [0.46, 0.97]
48 Hospitalization for gastrointestinal infection in first 12 months	1	3483	Risk Ratio (M-H, Fixed, 95% CI)	0.79 [0.42, 1.49]
49 One or more episodes of upper respiratory tract infection in first 12 months	1	510	Risk Ratio (M-H, Fixed, 95% CI)	1.07 [0.96, 1.20]
50 Two or more episodes of upper respiratory tract infection in first 12 months	2	3993	Risk Ratio (M-H, Fixed, 95% CI)	0.91 [0.82, 1.02]
51 Four or more episodes of upper respiratory tract infection in first 12 months	1	510	Risk Ratio (M-H, Fixed, 95% CI)	0.82 [0.52, 1.29]
52 One or more episodes of lower respiratory tract infection in first 12 months	1	510	Risk Ratio (M-H, Fixed, 95% CI)	1.07 [0.86, 1.33]
53 Two or more episodes of respiratory tract infection (upper or lower) in first 12 months	1	3483	Risk Ratio (M-H, Fixed, 95% CI)	0.90 [0.79, 1.03]
54 Hospitalization for respiratory tract infection in first 12 months	2	3993	Risk Ratio (M-H, Fixed, 95% CI)	0.75 [0.60, 0.94]
55 Number of episodes of otitis media in first 12 months	1	279	Mean Difference (IV, Fixed, 95% CI)	-0.04 [-0.49, 0.41]
56 One or more episodes of otitis media in first 12 months	2	3762	Risk Ratio (M-H, Fixed, 95% CI)	1.28 [1.04, 1.57]
57 Frequent otitis media in first 12 months	1	279	Risk Ratio (M-H, Fixed, 95% CI)	0.81 [0.43, 1.52]

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Comparison 5. Exclusive versus mixed breastfeeding > 7 months, developed countries, observational studies

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Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Very low density lipoprotein concentration (mmol/L) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	0.05 [-0.10, 0.20]
2 Low density lipoproteinconcentration (mmol/L) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	-0.10 [-0.88, 0.68]
3 High-density lipoprotein-2 concentration (mmol/L) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	0.08 [-0.05, 0.21]
4 High-density lipoprotein-3 concentration (mmol/L) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	Not estimable
5 Apoprotein B concentration (mg/dL) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	5.0 [-14.93, 24.93]
6 Total triglyceride concentration (mmol/L) at 9 months	1	26	Mean Difference (IV, Fixed, 95% CI)	0.3 [-0.23, 0.83]

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