Table 1

Accepted studies

Author and referenceStudy designTarget populationBreast milk exposureCognitive development assessment tool and participant ageResultsConfounders adjusted forDifference in IQ after adjustmentStudy quality grading
Amanda and Singh21Prospective cohort. Feeding method collected retrospectively84 school-aged children from two schools in IndiaExclusive breast milk for more than 4 months vs less than 4 months or formula fedGeneral mental ability test for children from 7–11 years (Srivastava and Saxena 1988–1989)There were significantly more breastfed (>4 m) children in the higher IQ category (IQ>109)NoneNot providedC
Andres et alLongitudinal study391 healthy infants enrolled in the Beginnings Study in Arkansas, USABreastfed vs soy fed vs milk-based formula fedAssessed at ages 3, 6, 9 and 12 months using the Bayley Scales of Infant Development (BSID) second edition, from which the Mental Developmental Index (MDI) and Psychomotor Development Index (PDI) were derivedBF infants scored slightly higher than formula-fed infants on the MDI score at ages 6 and 12 months (p<0.05). Confounders included in the modelSocioeconomic status, mother's age and IQ, gestational age, gender, birth weight, head circumference, race, age and diet historyBF infants scored 1–2 points higher than formula-fed infants on the MDI score at ages 6 and 12 months (p<0.05)A
Angelsen et al 200123Prospective cohort345 children in Scandinavia (Norway and Sweden)<3 months
3–6 months
>6 months
BSID at 13 months. Wechsler Preschool and Primary Scales of Intelligence (WPPSI-R), and Peabody Developmental Motor Scales (PDMS) at age 5 yearsShorter duration of breastfeeding was associated with lower scores on mental developmental tests both at 13 months and at 5 years of age. Unadjusted difference of eight pointsMaternal age, education, smoking and Raven score (IQ)Maternal age, education and intelligence were significant confounders. When analysing performance IQ and verbal IQ separately, the median IQ value was not statistically different when adjusting for maternal Raven scoreB
Auestad et al24Prospective randomised longitudinal study comparing different formula types and non-randomised breastfeeding group294 children from four sites in the USABreastfeeding until age 12 m, vs three different types of formulas (±AA, DHA)Bayley scale for infant development at 6 and 12 months
Fagan test of infant intelligence at 6 and 9 months
MacArthur communicative development inventories at 9 and 14 months
No difference in any of the parameters checked between any study groupsNoneNo difference in any of the parameters checked between any of the study groupsA
Auestad et al25Follow-up study of Auestad 2001: prospective randomised longitudinal study comparing different formula types and a non-randomised breastfeeding group157 children from the original 294 children from four sites in the USABreastfeeding until age 12 months, vs three different types of formulas (±AA,DHA)At 39 months, standard tests of IQ (Stanford Binet IQ), receptive vocabulary (Peabody Picture Vocabulary Test-Revised), and expressive vocabulary (mean length of utterance)No difference in any of the parameters checked between any study groupsNoneNo difference in any of the parameters checked between any study groupsA
Bartels et al26Retrospective cohort. Breastfeeding status prospectively assessed672 monozygotic male twin pairs
637 dizygotic male twin pairs
860 monozygotic female twin pairs
647 dizygotic female twin pairs
679 male–female twin pairs
598 female–male twin pairs in the Netherlands
<2 weeks
>2 weeks
Dutch CITO-elementary test at age 12 yearsBreastfed children of highly educated mothers score on average 7.6 points higher on a standardised test of cognitive abilities than formula-fed children of mothers with a low educationMaternal education, incomeA significant positive effect of breastfeeding on cognitive abilities above the expected positive effect of maternal education. Exact numbers not providedB
Bauer et al27Prospective cohort50 children from Honolulu, HawaiiBreastfeeding as a continuous variable over timeThe McCarthy Scales of Children's Abilities at age 3 yearsThe duration of breastfeeding was significantly correlated with scores on the scales, General, cognitive, Quantitative and MemorySocioeconomic status, gender and pesticide exposureRemained significant, numbers not providedC
Birch et al28Single-center, double-blind, randomised clinical trial comparing different formula types and non-randomised breastfeeding group52 healthy term infants enrolled for DHA and ARA supplementation and 32 breastfed infants served as controls in Dallas, Texas, USAAssigned diets were fed exclusively through 17 weeks of age. In the breastfeeding group, the average duration of breastfeeding was 43±9 weeksWPPSI-R was used to assess intelligence at 4 years of ageThe control formula and DHA-supplemented groups had Verbal IQ scores poorer than the breastfed group. There was no difference in performance or full-scale IQ between all groupsNoneNo adjustment carried outB
Bon29Retrospective cohort954 children from FranceExclusive bottle-fed vs breastfed for <15 days vs breastfed between 15 days and 2 months; vs breastfed for more than 2 monthsThe PM-47 Non-Verbal test, at 6–8.5 years of ageHigher scores for girls who were breastfed vs not breastfed. No difference in boysCould not be assessed from the textNot performedC
Bouwstra et al30A prospective, double-blind, randomised control study comparing different formulas. Non-randomised breastfed group as controlA control formula—n=169, an LC-PUFA supplemented n=146
Breastfed group n=159 in the Netherlands
Supplementation—2 months
All formula-fed infants received control formula between 2 and 6 months
BSID-II at 18 monthsBayley's MDI and PDI result values did not differ significantly between the three groupsParity, HOME score, parental EducationNo difference between the groupsB
Burruchaga et al31Prospective cohort39 children born at term and from homogeneous sociocultural status in SpainExclusive breast milk for at least 2 months, vs exclusive bottle-fedBSID at 22 monthsBayley's MDI and PDI result values did not differ significantly between the groupsMaternal education, head circumference, maternal occupation, birth order, smoking statusNo difference between the groupsC
Caspi et al32Retrospective cohort858 children from the New Zealand (Dunedin) birth cohort.
1848 children from the British (E-risk study) twin birth cohort
No breastfeeding
vs breastfeeding
New Zealand cohort: IQ measured at ages 7, 9, 11 and 13 years using Wechsler Intelligence Scale for Children–Revised. IQ scores combined for an overall score
British cohort: revised short form of WPPSI–age 5
Difference in IQ test scores between breastfed children and those not breastfed was 5.6 and 6.3 IQ points in the Dunedin and E-risk cohorts, respectively
Benefit mediated by a specific genotype. Only in children carrying the C allele
Genetic variation in fatty acid metabolism (rs174575)
Socioeconomic status, Maternal cognitive ability, Gestational age, birth weight
Children not carrying the C allele did not benefit from breastfeedingA
Clark et al33Prospective cohort784 Chilean children<2 months
2>8 months
>8 months
At age 5.5 years
WPPSI-R.
Preschool Language Scale—3rd Edition (PLS-3) the Broad Cognitive Abilities Standard Scale (BCA) of the Batería Woodcock-Muñoz-Revisada (Batería-R)
Poorer outcomes on the cognitive and language assessments were found for both the short and long extremes of breastfeeding as the sole milk source. The highest scores were observed in children who received breast milk as the sole milk source for 2–8 monthsGender, birth weight, child's age at testing, maternal education, IQ, depression, age, father's absence, paternal education, HOME score, socioeconomic status, nutritional status, iron deficiency anaemia at 12 months, and iron supplementationDifference in IQ not significantB
Daniels and Adair34Prospective cohort1984 Filipino childrenAny breastfeeding during:
0–6 months
6–12 months
12–18 months
18–24 months
Over 24 months
Philippines Non-verbal Intelligence Test of fluid abilities at ages 8.5 and 11.5 yearsPoor education and suboptimal living conditions among BF mothers were strong negative confounders, causing inverse associations between BF and cognitive ability. Increased duration of any BF was of small significant benefit for cognitive development at both agesParental education, paternal presence in home, maternal age, parity, alcohol during pregnancy, preterm status of child, mother reads, child's gender, baths (n/week), dietary variety at 2 years, household income, non-income-producing assets, electricity in home, and environmental hygiene score1.6 points among normal birth weight breastfed for 12–18 months vs less than 6 monthsA
De Andraca et al35Prospective cohort. Subanalysis of an RCT concerning iron fortified formulas788 infants, 4–6 months of age in Chile<30 days vs >30 days. All children in the study were breastfed for an average of 75 daysBSID—MDI and PDI at 12 months of ageBreastfeeding for more than 30 days was associated with significantly lower scores (2.5 points less in MDI and 2.3 in PDI). Probably due to low SESSES, education and occupation of parents, alcohol abuse, HOME, maternal intelligence by WAIS, stressful eventsNo adjustment was carried out for the specific association of breastfeeding and Bayley scaleC
De Andraca et al36Prospective cohort138 mother-infant dyad in ChileExclusive breastfeeding for 6 months or more vs weaning before 45 days of ageBSID at 12 months of ageNo difference between the groups in MDI and PDINone; study reports similar family characteristics in each groupNo differenceC
Der et al13Database analysis of a prospective study, sibling pairs analysis and metaanalysis5475 children
332 pairs of sibling discordant for breastfeeding status
545 discordant for duration of breastfeeding in the USA
Breastfeeding vs no breastfeeding. Breastfeeding history obtained mostly within a year of birthPeabody individual achievement test (PIAT) was administered to children between 5 and 14 yearsUnadjusted effect of breastfeeding +4.7 compared with non-breastfeedingMaternal IQ, education, age, family poverty, HOME stimulation score and birth orderAfter adjustment, the difference became non-significantA
Di girolamo et al37Prospective cohort. Breastfeeding data collected retrospectively80 children in SpainFull breastfeeding for at least 4 months vs no breastfeeding since 2 weeks of ageBSID at 8–30 monthsBreastfeeding group had a higher average MDI (of six points) compared with the bottle-fed group, but no difference in PDIParental education and age, gender, birth orderRemained significant. Data not providedC
Eickmann et al38Prospective cohort191 Brazilian infants‘Predominantly breastfed’ ‘partially breast fed’ and ‘non- breast fed’BSID-II at 12 months of ageFull breastfeeding at 1 month was associated with a small significant benefit in mental development compared with partial or no breastfeeding. No additional advantage in mental development was found with longer durations of full breastfeedingAdjusted for family income, possession of TV and fridge, flush toilet, maternal work and years of schooling, number of children under 5 years, home stimulation index, smoking during pregnancy, birth weight, infant's sex, haemoglobin, weight-for-ageFull breastfeeding at 1 month was associated with +3.0 points, p=0.02 compared with partial or no breastfeedingC
Elwood et al39Prospective cohort. Breastfeeding data collected retrospectively779 men from Caerphilly, South Wales, UKArtificially fed vs breastfed, duration unknown vs breastfed <3 months vs breastfed >3 monthsMen aged 60–74 years
The national adult reading test (NART)
The AH4 13 verbal and mathematical reasoning 3. The choice reaction time (CRT) for hand-brain reaction speed
In the normal birth weight group, the mean cognitive function was similar in both groups.
In the men whose birth weight had been below the median, having been artificially fed was associated with significantly lower results in two of the three tests
Age, social class, education, birth order and family size, father's social class, father's unemploymentIn the normal birth weight group, the adjusted mean cognitive function was similar in both groupsB
Evenhouse and Reilly40Database analysis of a prospective study, sibling pairs analysis. Data from the National Longitudinal Study of Adolescent Health2734 sibling pairs in the USANo breastfeeding <3 months 3–6 months 6–9 months 9–12 months 12–24 months >24 monthsAdd Health's abbreviated version of the Peabody Picture Vocabulary Test (PVT), normed for age and sexPersistent positive correlation between breastfeeding and cognitive ability
Unadjusted Difference in PVT 4.9 centile points when comparing never breastfed to any breastfeeding in the full sample
Birth weight, gender, birth order, parental investment, environmental characteristics1.68 centile points higher for ever breastfed to never breastfedA
Fergusson et al41Prospective cohortBirth cohort of children from the Dunedin Multidisciplinary Child Development Study:
1037 children assessed at age 3 years
991 at age 5 years
954 at age 7 years
Child bottle-fed; Breast-fed for up to 4 months; Breastfed for 4 months or longer.Measures of intelligence at 3, 5 and 7 years.
3 years-Peabody Picture Vocabulary Test 5 years-Stanford Binet Intelligence Scale
7 years-Weschler Child Intelligence Scale
Children who were breastfed for 4 months or longer had scores which were 3.84 (average) points higher than bottle-fed infants (on scales with an SD of 10)Maternal intelligence (SRA verbal scale), maternal education, childhood experiences. Maternal training in child-rearing, family socioeconomic status. Birth weight and gestational ageA small but statistically significant benefit in the test scores of breastfed vs Bottle-fed infants (mean=1.89)A
Florey et al42Retrospective cohort592 firstborn singletons in DundeeBreastfed on discharge from the hospital vs Bottle-fedAge 18 months. Bayley Scales of Infant Mental and Motor DevelopmentHigher mental development was significantly related to breastfeeding on discharge from hospitalPartner's social class, mother's education, height, alcohol and cigarette consumption, placental weight and the child's sex, birth weight and gestational age at birthAfter adjustment, the difference in the Bayley mental development index between the groups was between 3.7 and 5.7 unitsC
Foroushani et al43Longitudinal cohort. Breastfeeding data collected retrospectively at age 2 years5362 singletons born in 1946 in England, Wales and ScotlandNo breastfeeding
1–3 months
4+ months
Age 8—sentence completion, reading and vocabulary
Age 11—Verbal, reading and vocabulary.
Age 15—Verbal, reading and vocabulary.
Age 26—reading
Age 43—visual and memory
Children who were breastfed longer scored higher on verbal tests. Tests at older age (26, 43) were not significantly differentBirth weight, childhood illness, home conditions, parents’ age and education, child's behavioural scores, parents interest in the child's development, school typeMean score 1.5 points higher for ages 8, 11, 15. Not significant at older agesC
Gale and Martyn44Prospective cohort994 men and women, born between 1920 and 1930 in Hertfordshire, UKExclusive breastfeeding, exclusive bottle feeding, mixed feeding65–75 years old. AH4 IQ test, taken on a computerParticipants who had been exclusively breastfed had slightly higher IQ scores compared with the two other groupsThe use of a dummy in infancy, number of older siblings, father's occupational class, and mother's age at the participant's birthAfter adjustment, no association was found between adult intelligence and method of infant feedingB
Gale et al45Prospective cohort241 children born to the Southampton Women's Survey, UKBreastfeeding
Fortified formula feeding
Unfortified formula feeding
Age 4—WPPSI (3rd edn.), sentence repetition and verbal fluency measured by NEPSYIn unadjusted analysis, children who were breastfed or fed with a fortified formula had significantly higher scoresMaternal IQ and education, social class, on benefits, age at birth, birth weightAfter adjustment, the differences in IQ between groups became non-significantA
Ghys et al46Prospective cohort. Data on breastfeeding collected retrospectively128 full-term children in the NetherlandsBreastfeeding was expressed as the number of months of breastfeeding regardless of possible additional formula feedingAt 4 years: Dutch adaptation of the Kaufman Assessment Battery for Children (K-ABC), the Groningen Developmental Scale (GOS). And items of the motor scale of the McCarthy Scales of Children's Mental AbilitiesDuration of breastfeeding showed significant correlations with cognitive development (Pearson correlation coefficient 0.26)Plasma and RBC DHA and AA, maternal intelligence, birth weight, duration of breastfeeding and paternal educational attainment, smoking during pregnancyIn the regression analysis, the correlation disappearedB
Gibson-Davis and Brooks-Gunn 47Longitudinal birth cohort study. Breastfeeding information collected retrospectively at 1 year1645 American-born mothers and their babiesBreastfeeding for at least 1 month vs noneAt 3 years of age: Peabody Picture Vocabulary Test-Third EditionIn unadjusted mean comparisons, breastfed children had Peabody Picture Vocabulary Test scores that were 6.6 points higher than children who were not breastfedAn extensive set of demographic characteristics, including mother's Peabody Picture Vocabulary Test and the Home Observation for Measurement of the Environment score. Mothers were categorised into one of three educational-status groupsAfter adjusting for demographic characteristics and maternal verbal ability, the coefficient dropped to 1.72A
Gomez-Sanchiz et al48Prospective cohort, information on feeding collected retrospectively238 healthy babies born at term, non-IUGR in SpainFormula fed, Breastfed up to 4 months, Breastfed for more than 4 monthsBayley Infant Development Scale at 24 months of ageInfants breastfed for longer than 4 months scored higher on the mental development scale than those breastfed for less timeSociodemographic and neonatal variables including parental IQ scoreThe results of multiple linear regression analysis showed that infants breastfed for longer than 4 months scored 4.3 points more than those breastfed for less timeA
Greene et al49Retrospective cohort432 participants. 208 males, 224 females in IrelandBreastfed vs non-breastfed
And
Breastfed for up to 12 weeks vs more than 12 weeks
Age: 11–16 years
Raven's Standard progressive matrices test and subsets of the Primary Mental Ability Test namely verbal meaning, reasoning and number facility
The breastfed children showed a highly significant advantage over the non-breastfed children for all measures of IQ assessed, ranging from a 4.3 point advantage in Raven's IQ to a 6.0 point advantage in Primary mental abilities IQBirth weight, gestational age, birth rank, child's sex, social class, mother's age and mother's educational levelFollowing adjustment, the beneficial effect of breastfeeding (yes vs no) was statistically non- significant. A six point advantage in verbal IQ and 5.4 point advantage in reasoning IQ were observed for participants breastfed for >I 2 weeks, compared with lessC
Gurka et al abstract50Prospective cohort1050 children, from the National Institute of Child
Health and Development Study of Early Child Care and Youth
Development in the USA
Never;
0–6 months; longer than 6 months
Age: 4 years old
Standardised (mean.100; SD.15) cognitive outcomes
Significant positive associations were observed between breastfeeding and cognitive outcomes before adjusting for other factorsMaternal age, education, observed quality of the home environment, mother's attitude regarding modernity of parenting, and maternal verbal IQNo difference between the groupsA
Hart et al51Prospective cohort83 healthy full-term infants in Texas, USAExclusively breastfed vs exclusively non-breastfedBrazelton Neonatal Behavioral Assessment Scale (BNBAS) at a mean age of 8.95 daysBreastfed infants surpassed formula-fed infants on items of orientation, motor, range of state, and state regulation dimensions of the BNBAS. Breastfed infants also exhibited fewer abnormal reflexes, signs of depression and withdrawalSocioeconomic statusAfter adjustment for SES only, the differences remained significantB
Hoefer and Hardy9Retrospective cohort383 children in Illinois, USAArtificially fed, breastfed for 3 months or less, from 4 to 9 months and from 10 to 20 monthsAge—7–13 years. Stanford Revision of the Binet-Simon intelligence test and the Pintner-Patterson performance scale (a nonverbal intelligence test), and by a group educational test, the Stanford achievements testInfants artificially fed were inferior in all standardised measurements to those breastfed from 4 to 9 months, and, with one exception, to those breastfed 3 months or less. Those artificially fed equalled or excelled those breastfed from 10 to 20 monthsnone; similar paternal IQAdjustment was not carried out, although they mention that paternal IQ was similar between the groupsC
Holme et al52A secondary analysis of data from a follow-up study of an RCT of an intervention to reduce smoking in pregnancy1218 children in Birmingham, UKNot breastfed, Breastfed up to 2 months, 2–4 months, over 4 months.
Also, any breastfeeding vs none
British Ability Scales (Total IQ, Visual IQ, and verbal IQ), and Quick Neurological Screening Test (QNST) at age 9 yearsBefore adjustment, breastfeeding was significantly associated with higher total, verbal and visual IQ scores, and increasing duration was significantly correlated with IQ scoresBreastfeeding was associated with a crude total IQ increase of 5.49 points, which was reduced to 1.78 points on analysis with breastfeeding as a binary variable (yes/no—still significant)Maternal demographics (including education, race and age), smoking history, work patterns, depression, social support, neonatal details and ill-health in the childTotal IQ became non-significant after adjustmentA
Horwood and Fergusson53Longitudinal study—children studied at birth, 4 months, 1 year, at annual intervals to age 16, and 18 years1064 children born in New Zealand in 1977Not breastfed, breastfed for <4 months, breastfed for 4–7 months, breastfed for ≥8 monthsRevised Wechsler Intelligence Scale for Children (total IQ)—age 8 and 9
Teachers’ rating of school performance (reading and mathematics)—age 8 and 12
Progressive Achievement Test of Reading Comprehension—ages 10 and 12
Progressive Achievement Test of Mathematics—age 11
Tests of scholastic abilities—age 13
High School Outcomes
Increasing duration of breastfeeding was associated with consistent and statistically significant increases in cognitive abilities, and children who were breastfed for ≥8 months had mean test scores that were between 0.35 and 0.59 SD units higher (more than 5 points) than children who were bottle-fedMaternal age, maternal education, family socioeconomic status, averaged standard of living, averaged family income, maternal smoking during pregnancy, gender, birth order, birth weightUpon adjustment, associations were reduced and children who were breastfed for ≥8 months had scores that were 0.11–0.3 SD units (less than three points) higher than children who were bottle-fedA
Innis et al54Retrospective cohort433 full-term infants born in 1994 in VancouverNever breastfed, breastfed less than 1 month, 1–3 months, 3–6 months, 6–8 months, more than 8 months, and mixed feeding (breast and formula milk)Visual acuity measured using acuity card procedure with Teller Acuity Cards. Cognitive development measured using the Fagan Test of Infant Intelligence, (V.4.1) at 39 ±1 weeks of ageThere were no differences in visual acuity or novelty preference among the infants when they were stratified by incidence or duration of breastfeedingNoneNo differenceB
Jacobson et al55Prospective Longitudinal study323 predominantly white, middle-class children born from 1980 to 1981, at age 4, and 280 children at age 11, from two cohorts of similar demographic information in Michigan, USA
*Most exposed to PCB during pregnancy
Breastfed vs not breastfedMcCarthy Scales of Children's Abilities and the Peabody Picture Vocabulary Test-Revised at the age of 4
Wechsler Intelligence Scale for Children-III, Wide Range Achievement Test-Revised, and the Woodcock Word, Passage, and Reading Comprehension test at the age of 11
At the ages of 4 and 11, breastfeeding was significantly related to higher IQ scoresSocial class, education, maternal IQ, parenting skills (Home observation for measurement of the environment (HOME))The relationship was reduced to non-significance after adjustment for maternal IQ and parenting skills (HOME)B
James56Prospective cohort38 full-term children (taken as a sample from an extended Pembrokeshire farming family, UK)Bottle-fed babies vs breastfed babiesIQ test At age 16 (no details)No difference in IQNo adjustmentNo differenceC
Jedrychowski et al57Longitudinal study468 term babies in Krakow, PolandComplementary breastfeeding (including none), vs exclusive breastfeeding up to 3 months, 4–6 months, or longer than 6 monthsIn the first 3 years of the follow-up, the Bayley Mental
Scales of Infant Development-second edition (BSID-II) were used. At the age of 6 and 7, the Wechsler intelligence test for children (WISC-R) was administered
Children on mixed breastfeeding achieved lower total IQ scores at each of the IQ check-ups compared with those who were exclusively breastfedMaternal education, baby's gender, parity, and weight gain in pregnancyChildren breastfed exclusively for >6 months increased by 3.8 points (95% CI 2.11 to 5.45)B
Jiang et al58Longitudinal study3271 children and their mothers from the USA participating in the Child Development Supplement of the Panel Study of Income DynamicsYes or no ever breastfeeding and, never breastfed; less than 6 months, 7–12 months, and more than 12 monthsWoodcock Johnson Psycho-Educational Battery-Revised (WJ-R) test score and Wechsler Intelligence Scale for Children-Revised (WISC-R) test score at 3 and 6 years of ageBreastfed children had higher scores on WJ-R and WISC-R testsChild's age, race and ethnicity, sex, number of siblings, whether the child was first born to the mother, whether the child was born preterm, whether the child was born SGA, HOME scale, maternal IQ, age, education, health status, insurance, marital status, working, incomeThree out of the five effects remain significant; the effect sizes are smaller, with only one effect size being larger than one-fifth of the SD. Longer spells of breastfeeding are uncorrelated with increases in the measures of achievementA
Johnson et al59Longitudinal study204 Euro-American full-term infants were followed up to the age of three from the Galveston (Texas) areaBreastfed vs not breastfed
AND
Duration of breastfeeding
At age 3 years; Stanford-Binet Fourth Edition and Peabody Picture Vocabulary Test-RevisedBreastfeeding added significantly to the prediction of the Composite IQ Comprehension factor, Vocabulary, Absurdities, Memory for Sentences, and Peabody Picture Vocabulary Test-Revised. Duration of breastfeeding only added to the prediction of Vocabulary scoresSocioeconomic status, HOME scores (parenting skills), mother's intelligence, mother's smoking behaviour, gender and birth order of the childBreastfeeding was associated with a 4.6-point higher mean in the children's
Intelligence
A
Keim et al- abstract60Prospective cohort347 children in the USAExclusively breastfed vs formula fedMullen Scales of Early Learning at 1 year of ageInfants exclusively breastfed demonstrated better visual reception, fine motor and overall cognitive development at 12 months than formula fed infants (4–6 points)Preterm birth, smoking, race/ethnicity, educationDifferences were weakened after adjustment. No numbers provided in the abstractC
Kramer et al15Cluster-randomised trial.13 889 Belarussian children born between June 1996 and December 1997Experimental group vs control group: Experimental group was encouraged to breastfeed and had greater levels of breastfeeding at 3, 6, 9 and 12 months (exclusive breastfeeding also sevenfold higher at 3 months)Wechsler Abbreviated Scales of Intelligence and teacher evaluations of academic performance in reading, writing, mathematics and other participants at 6.5 years of ageThe experimental group had higher means on all of the Wechsler Abbreviated Scales of Intelligence measures, with cluster-adjusted mean differences of 7.5 points for verbal IQ, 2.9 points for performance IQ, and 5.9 points for full-scale IQ. Teachers’ academic ratings were significantly higher in the experimental group for reading and writingMaternal (and paternal) IQ, as well as all other demographic and confounding variables, should be distributed randomly between the treatment groups and should not confound the treatment effectCluster-adjusted mean differences of 7.5 points for verbal IQ, 2.9 points for performance IQ, and 5.9 points for full-scale IQA
Lawlor et al61Prospective cohort3794 woman who delivered a singleton baby between 1981 and 1984 in Brisbane, AustraliaNever, <4 months, ≥4 monthsPeabody Picture Vocabulary Test at the age of 5 Raven's standard progressive matrices (Raven's SPM) and the Wide Range Achievements Test V.3 (WRAT3) at 14 yearsUnivariate analysis of breastfeeding vs IQ showed a significant difference between the breastfeeding groups (higher scores associated with longer breastfeeding up to 8.6 points difference)Gender, maternal age, maternal ethnicity, maternal education, paternal education, family income, gravidity, maternal smoking, fetal distress, duration of the first and second stages of labour, mode of delivery, apgar scores at 1 and 5 min, birth weight for sex and gestational age (z score), height for age and sex (z score), BMI for age and sex (z score)Significance remained with a mean difference in IQ of 6.8 between never and over 4 months of breastfeedingA
Lucas et al62A prospective, double-blind RCT (different formulas, breastfed control group not randomised)447 healthy full-term children born in the UK between 1993 and 1995Breastfed for at least 6 weeks vs formula fedBSID-II at 18 monthsNo differences in overall developmental scores at 9 months or 18 months or in any subscale quotient at 9 months were foundSex, centre, maternal age, maternal education, maternal marital status, and social classNo difference with adjustment for potential confounding factorsA
Maimaitiming and Wang63Retrospective cohort442 infants and children inhabited by Uygur, Han or Kazak nationality in West ChinaBreastfed vs mixed feedingDenver Developmental Screening Test at age up to 3There were no differences in scores between breastfeeding vs mixed feeding groupsNoneNo differenceC
Makrides et al64A prospective, randomised, double-blind controlled. Different formulas. Breastfed group was used as control, but not randomised68 formula-fed infants and 46 breastfed infants born at term of appropriate weight in AustraliaFormula fed vs breastfedInfant VEP acuity at 16 and 34 weeks
Bayley's Scales of Development at 1 and 2 years
At 1 year of age, MDI scores of breastfed and formula-fed infants were not different, but at 2 years of age, MDI scores of breastfed infants were higher than those of formula fed infants. PDI scores were similarHome screening questionnaire scores, occupational prestige, parental education, gender, birth weight, maternal smoking, birth order, feeding modeMDI score was higher at age 2 in the breastfed group. 95% CI 3 to 16.8A
Malloy and Berendes65Retrospective cohort518 children born in 1978–1979 in Washington DC who were exposed to chloride-deficient formulasNo breastfeeding (176) vs any time length of breastfeeding (342)Weschler Intelligence Scale-Revised at 9 or 10 years of ageBreastfed scored significantly higher on full-scale IQ; Further analyses limited to those exclusively breastfed for the first 60 days failed to demonstrate any significant relationshipMaternal education, paternal education and annual incomeFollowing adjustment, the difference was not significantB
Martin et al66Retrospective cohort1431 children (twin siblings) from the greater Brisbane areaExclusively formula fed, any breastfeeding between birth and 3 months, exclusively breastfed for 3–6 months, exclusively breastfed for 6 months or moreFSIQ (full-scale IQ) assessed using the Multidimensional Aptitude Battery (MAB) at 16 years of ageBreastfeeding was significantly associated with FSIQ scores. No effect of duration of breastfeeding on FSIQ was foundSocioeconomic status, paternal education, maternal education, gestational age and birth weightThe effect was no longer significant after adjustmentA
McCrory and Layte67Retrospective cross-sectional study8568 school children in Ireland born between 1997 and 1998Breastfed vs not breastfed
AND
Never breastfed, ≤5 weeks, 6–15 weeks, 16–25 weeks, 26+ weeks
Age 9 years. Vocabulary component of the Drumcondra Primary Reading Test-Revised and part 1 of the Drumcondra Primary Mathematics Test-RevisedIn unadjusted analysis, children who were breastfed scored 8.67 percentage points higher on reading and 7.42 percentage points higher on maths. Evidence of dose–response relationship was weakGender, birth weight, gestation period, NICU, primary and secondary carer's social class, primary carer's education level, household income, mother's age at birth, Irish/Non-Irish, number of children's books in the homeAfter adjustment, remained significant but weakened: 3.24 and 2.23 percentage points in reading and maths, respectivelyA
Morales et al68Retrospective cohort analysing polymorphisms in genes encoding enzymes involved in LC-PUFA synthesisTwo population-based birth cohorts n=400 mother-child pairs from INMA-Sabadell; and n=340 children from INMA-Menorca in SpainDifferent types of formula fed vs breastfedMental development was assessed at age 14 months using the BSID, first Edition—MDI only, and at age 4 years by the Spanish version of the McCarthy Scales of Children's Abilities (MCSA)Children with variants associated with lower synthesis of LC-PUFA had higher scores when breastfed, while those with greater capacity to synthesise these fatty acids had higher scores regardless of breastfeeding practicesSex, child age, psychologist, quality of neuropsychological test, maternal education, breastfeeding, and use of gas stove at homeNot being breastfed conferred an 8-point to 9-point disadvantage in cognition among children with low FADS1 activity and a 5–8-point disadvantage in cognition among children with low ELOVL5 activityA
Morris et al69Prospective cohort102 normal birth weight children born in Brazil at termNumber of breastfeeds per day (recorded daily)BSID at 6 months and 12 months (MDI and PDI)Breastfeeding frequency over the first 4 weeks of life, but not later, was significantly associated with mental development (MDI) at 6 months of ageSocioeconomic data: family income, a household resources index, a housing quality index, a water and sanitation index, and maternal and paternal literacyAn average of one extra breastfeed per day resulted in an increase of approximately one-quarter of a point. The effect was no longer apparent at 12 months of ageB
Morrow-Tlucak et al70Prospective cohort229 children born in Ohio between 1981 and 1982No breastfeeding, breastfeeding=<4 months, breastfeeding >4  monthsBSID—MDI at 6 months, 1 year and 2 years of ageSignificant differences in MDI scores between the three groups (longer breastfeeding=higher scores) at 1 and 2 years of age (no significant difference at 6 months)Parent education (mean of both parents), maternal attitude (Authoritarian Family Ideology), maternal intelligence (PPVT-R), cigarette use, maternal age, rage, marital status, Home Observation for Measurement of the Environment (HOME) at age 1, HOME at age 2, exact age at time of testingWith covariate control, a small but significant relationship between duration of breastfeeding and Bayley MDI at 1 and 2 years was detected. Infants breastfed for 4 months or more scored on average nine points higher compared with the bottle-fed infantsA
Mortensen et al71Prospective longitudinal birth cohortMixed sample: 973 men and women
All-male sample: 2280 men in Denmark
Divided into five groups: <1 month 2–3 months 4–6 months 7–9 months >9 monthsWechsler Adult Intelligence Scale (WAIS) at a mean age of 27.2 years in the mixed-sex sample.
Børge Priens Prøve (BPP) test at a mean age of 18.7 years in the all-male sample
Duration of breastfeeding was associated with significantly higher scores on the Verbal, Performance, Full Scale WAIS IQs and BPP testParental social status
Parental education
Single mother status
Mother's height, age and weight gain during pregnancy cigarette consumption during the third trimester number of pregnancies
Gestational age birth weight
Birth length
Indexes of pregnancy
Delivery complications
The results remained significant with 4.6 points higher IQ for those breast-fed over 9 months compared with those breastfed for less than 1 monthB
Mukerji et al72Cross-sectional study100 children aged 0–3 years in IndiaNo breastfeeding or mixed.
Exclusive breastfeeding for 4–9 months.
Exclusive breastfeeding for more than 9 months
Developmental Screening Test (DST)In the 4–9 months exclusive breastfed group, 100% had average or above average IQ.
In the two other groups this number was significantly lower
NoneNo adjustments were madeC
Nassar et al73Cross-sectional study42 healthy infants in Cairo, EgyptBreastfed, artificially fed, mixed feedingBayley scale of infant development-second edition (BSID-II) between 4 and 6 months of ageNo difference in MDI or PDI. There was significant difference only in the total behaviour rating scale (TBRS) and motor quality centile rankNo significant difference between groups in terms of age, sex, and socioeconomic standard (indirectly adjusted for with multiple regression)Significant increase in mean adjusted TBRS and motor quality centile rankB
Nelson et al74Prospective cohortTerm gestation infants in USABreastfed or formula fed for 3 monthsTeller Acuity Cards at 14 days, 3, 4, 8, and 18 months
Fagan Test of Infant Intelligence at 8, 10 and 12 months
BSID at 4, 8 and 18 months
There were no significant differences between breastfed and formula-fed infants in visual acuity at 14 days, 3, 8 or 18 months, or recognition memory or the Bayley PDI or MDI at any ageMeeting abstract only availableC
Niemela and  Jarvenpaa 75Prospective follow-up726 children born between 1985 and 1986 in FinlandBreastfed <5 months, breastfed >5 months (matched pairwise based on maternal education and sex)Non-verbal Columbian Mental Maturity Scale (CMM), visual integration using the Beery test and active vocabulary by naming of pictures at 56 monthsChildren breastfed for 5 months or more attained higher scores in developmental tests (significance difference found in relation to the general cognitive capacity and visual motor integration). No evidence of any interaction between verbal development and breastfeeding to 5 months or moreGroups matched pairwise based on sex and maternal educationMaternal education and parental status correlated with all cognitive scores. Sex and breastfeeding correlated with scores of the general cognitive capacity and visual motor integration tests in multiple linear regressionsB
Oddy et al76Prospective cohort1401 children at first follow-up and 1283 children at second follow-up from the Western Australian Pregnancy Cohort Study following 2860 children in Perth, AustraliaNever breastfed, fully breastfed 0–4 months, 4–6 months, more than 6 monthsPeabody Picture Vocabulary Test-Revised (PPVT-R) for receptive English vocabulary—verbal intelligence at 6 years
Performance subtest by the Wechsler Intelligence Scale for Children—Third Edition (WISC-III)—Block Design Test at age 8 years
On average, children breastfed for more than 6 months had mean verbal IQ scores that were 644 points higher and Block Design scores that were 1.13 points higher than children never breastfed (small but significant differences)Gestational age, maternal age, maternal education, parental smoking and older siblings (all covariates that were significantly correlated with verbal IQ and the performance subtest or breastfeeding)Breastfeeding for >6 months was associated with an increase in verbal IQ of 3.56 points. The Performance subtest was weakened and was no longer a significant difference after adjustmentA
Oddy et al 77Prospective cohort980 children from the Western Australian Pregnancy Cohort Study following 2860 children in Perth, AustraliaBreastfed less than 4 vs more than 4 months and breastfed less than 6 vs more than 6 monthsWestern Australian Monitoring Standards in Education (WAMSE) scores in: maths, reading, writing and spelling at age 10 yearsContinuous breastfeeding was significantly associated with an increase in scores with each additional month of breastfeeding for maths, reading, writing and spellingGender, maternal age, maternal education, family income, marital status, parent looks at book with child at age 5, maternal country of birthResults were attenuated when adjusted for confounders. Significant interactions were found in maths and spelling, revealing that boys were more likely to have improved academic scores if breastfed for a longer periodA
Paine et al78Retrospective cohort96 healthy full-term Caucasian children from the Adelaide area in AustraliaDuration of exclusive breastfeedingBayley Scales of Infant Development at age 10–14 monthsDuration of exclusive breastfeeding significantly predicted mental development scores for boys, but not for girls. Duration of breast-feeding did not predict psychomotor development scoresDuration of breastfeeding, parents’ occupational prestige, parents’ education level and smoking habits, number of siblings, birth order, HSQ score, gestational age, birth weight, age of testing, maternal age and gender were considered as possible independent variables—independent variables with p<0.02 included in the model—gender, maternal age, birth weight and duration of breastfeedingNoneC
Pollock79Prospective cohort3838 children from the 1970 British Births Survey at full term and healthy birth weightWholly breastfed for more than 3 months vs wholly bottle-fedHuman figure drawing score, copying design score and English Picture Vocabulary Test score at age 5. Dichotomised outcomes: Pictorial Language Test, Friendly Maths test, Edinburgh Reading test, Spelling Test, British Ability Scales (Word definitions, similarities, matrices, total) and Continuous outcomes: Pictorial Language test, Friendly Maths test, Edinburgh Reading test, Spelling test, and British Ability Scales (Word definitions, similarities, matrices, total) at age 10Significant difference found between groups at age 5 for the English Picture Vocabulary test.
Significant difference found for dichotomised outcomes and continuous outcomes for the British Ability Scales and dichotomised outcomes for the Pictorial Language test at age 10
Age father left full time education, age mother left full time education, highest educational qualifications of mother, mother's smoking behaviour during pregnancy, antenatal labour preparation class attendance, infant's place of birthAll results adjusted for all other independent predictors of breastfeeding: English Picture Vocabulary test: aOR 1.50. Dichotomised outcomes:
Pictorial Language test aOR 1.49
Word definitions aOR 1.55
Similarities aOR 1.64
Total aOR 1.64
Continuous outcomes:
Word definitions mean diff 3.5
Matrices mean diff 2.6
Similarities mean difference 3.0
Total mean difference 3.1
A
Quinn et al80Prospective cohort3880 healthy children from the Mater Hospital-University of Queensland Study of Pregnancy projectNever breastfed, <3 weeks, 3–7 weeks, 7 weeks—4 months, 4–6 months, still breast feeding at 6 monthsPeabody Picture Vocabulary Test Revised (PPVT-R) at 5 years of ageSignificantly increasing scores were found between duration of breastfeeding and the PPVT-R scoresBirth weight, poverty, maternal education, maternal age, time in daycare/preschool, number of children in household at 5 years, English speaking background for mother and father, and degree of infant stimulationAfter adjusting for a wide range of biological and social factors, the adjusted mean for those breastfed for 6 months or more was 8.2 points higher for females and 5.8 higher for males when compared with those never breastfed (this was significant)A
Rao et al81Prospective cohort299 children born in Norway/Sweden at appropriate size for gestational age (comparison group)<12 weeks vs >12 weeks of breastfeeding
AND
Duration of breastfeeding as a continuum
BSID at 13 months of age
Norwegian version of the WPPSI-R at 5 years. of age
Peabody Development Motor Scale measured at 5 years of age
There were statistically significant differences in IQ between the 2-breastfeeding groupsSite of enrolment, maternal education, maternal IQ, maternal smoking, admission to a neonatal intensive care unit, kindergarten attendance, gender and asymmetric intrauterine growth retardation3.7 points for total IQ and 4.1 points for performance IQ. Results remained unaltered when adjusted for confounding variablesB
Ribas-Fito et al82Prospective cohort391 children born in Spain between 1997 and 19990–2 weeks breastfeeding 2–20 weeks breastfeeding 20+ weeks breastfeedingSpanish version of the McCarthy Scales of Children's Abilities (general cognitive scale, verbal scale, perceptual-performance scale, memory scale, quantitative scale, motor scale subsets) at 4 years of ageChildren with longer periods of breastfeeding performed significantly better on the McCarthy cognitive scale (except motor)Gender, academic trimester at examination, psychologist, maternal social class, maternal education, and maternal use of alcohol and tobacco during pregnancyAfter adjustment for confounders, significance remained for the general cognitive scale, and a trend remained in other subsetsA
Richards et al83Retrospective cohort1741 people from the MRC National Survey of Health and Development (NSHD), also known as the British 1946 birth cohortNever
Up to 2 months
2–7 months
7+ months
National Adult Reading Test (NART), word-list learning task (verbal memory) and timed letter search task (mental speed and concentration) at age 53Educational Attainment: odds of obtaining higher qualifications by the age of 26 were statistically significant, with greater odds for longer breastfeeding
Cognitive Function: regression coefficients for the unadjusted effect show that breastfeeding was significantly associated with the NART and verbal memory tests
Early background variables:
Sex, father's social class, mother's education, birth order, parental interest in education and material home conditions
Effect of BF on education was strengthened after adjusting for the early background variables and remained significant. No longer significant with further adjustment for cognitive ability at age 15
Cognitive function: Coefficients were reduced after adjusting for the early background variables and were further reduced after adjusting for educational attainment and adult social class Only NART remained significance
A
Richards et al84Retrospective cohort511 first-born offspring of the British 1946 cohort and their parentDuration of breastfeedingSentence completion test, reading test and vocabulary test at age 8 yearsBreastfeeding was positively associated with cognitive function at age 8 in the first offspring of a national birth cohort. This association was not evident in the subsample of mothers of these offspring. Association in the offspring cohort became non-significant after adjusting for social class, maternal education or maternal cognitive performanceSocial class, parental educational attainment, material home conditions, maternal age at birth, birth order, family size, maternal cigarette smoking, parental interest in education, attendance at nursery school, whether offspring cohort members had been taught cognitive skills at age 4, and cognitive test scores of the mothersNon-significant; after adjusting for social class, maternal education or maternal cognitive performanceC
Rodgers85Longitudinal study1464 children at age 8 and 1398 children at age 15 from the British 1946 cohortNever bottle-fed vs never breastfedPicture intelligence test and word reading test at 8 years of age
Non-verbal ability, mathematics and sentence completion tests at age 15 years of age
A preliminary analysis indicated that low scores were more likely for those who had been bottle-fed than breastfed. The mean sentence completion scores between the two groups are statistically significant. Every test at both ages was significant except for word reading scores after correction for background factorsSex, social group, parental interest in education, material home conditions, sample stratification, father's education, mother's education, family size, birth rank, age at weaningAfter correction for confounders, every test at both ages was significant except for word reading scoresB
Rogan and Gladen86Prospective cohort855 newborns being followed in North Carolina were enrolled between 1978 and 1982 and followed up to 5 years oldBottle-fed
‘short breastfeeding’ ‘medium breastfeeding’ ‘long breastfeeding’ ‘very long breastfeeding’
Bayley Mental and PDI at 6, 12, 18 and 24 months of age. McCarthy General Cognitive, Verbal, Quantitative, Memory, Perceptual Performance and Motor scales at 36, 48, and 60 months of age Report Card Grades from 3rd, 4th and 5th grade (averaged)Bayley Mental and Psychomotor: After adjusting for covariables, the results at all four time points were similar and differences among the groups were only statistically significance at 24 months
McCarthy: All scales showed trends towards higher scores with increasing length of breastfeeding, but the relationship was weakest for the motor scale. Differences after adjustment were only significant at 3 and 4 years (marginally at 5 years) between length of breastfeeding groups
Report Cards:
Showed slight increase with breastfeeding. Marginally significant after adjustment for English scores and not significant for maths
Age, race, occupation, education, smoking, drinking, child's sex, birth weight, number of older siblings, prenatal PCB exposure and dichlorodiphenyl dichloroethene exposure, identity of the examinerConfounders integrated into model; unadjusted results not shownB
Santiago Burruchaga et al87Prospective cohort39 children born at term and from homogeneous sociocultural status in SpainBreastfed for at least 2 months vs formula fedBayley's scale at 2 years of ageNo statistically significant differences between groups were found in cognitive functionMaternal age, level of education, occupation, number of children in the family, smokingNone; confounders integrated into modelC
Silva et al88Longitudinal population-based cohort9367 children from the 1970 British Cohort Study comprising individuals born during April 5–11 in the UKNever breastfed
Less than 1 month
1–3 months
More than 3 months
British Ability Scale, the Shortened Edinburgh Reading Test (word recognition), the Friendly Math Tests, and the Pictorial Language Comprehension Test at the age of 10 yearsBreastfeeding showed a positive association with cognition at 10 years before adjustmentSocioeconomic class, birth weight, parity, gestational age, maternal age and maternal smokingBreastfeeding was weakly associated with cognitive function after adjustment (standardised coefficient 0.07). However, this effect was much smaller in the structural equation model adjusting for the same variables and did not reach significance level, suggesting that it is of little clinical importanceA
Silva et al89Retrospective cohort1037 children from the Dunedin Multidisciplinary Child Development Study<1 week
1–4 weeks
5–12 weeks
13–24 weeks
25–36 weeks
37–51 weeks
51+ weeks
Gross motor co-ordination, fine motor co-ordination, verbal comprehension and verbal expression, intelligence, child behaviour problems at age 3 yearsComparison of the groups resulted in only one significant difference among 96 comparisons made. No significant differences in age of attainment of milestones, gross or fine motor ability scores, verbal comprehension or expression, ability, intelligence, the incidence of separation problems, hyperactivity, height, weight and head circumferenceSocioeconomic class, general mental ability (IQ), level of education
Pairwise comparison with group matching to account for confounders
None; pairwise matching said to account for confoundersB
Sloan et al90Cross-sectional observational. Breastfeeding data were obtained retrospectively137 infants and mothers in IrelandBreastfed (defined as more than 1 month) vs not breastfed (defined as less than a month or not at all)BSID (second edition; Bayley, 1993), between 10 and 18 months of ageMean cognitive scores were significantly higher in breast-fed infants (110) compared with formula-fed infants (105). Breastfeeding duration had a positive linear association with cognitive scores at 1 yearHome environment (HOME score) and infant genderThe adjusted standardised β for breastfeeding was 0.285, which remained significant after adjustmentC
Slykerman et al91Cross-sectional observational. Breastfeeding data were obtained retrospectively550 infants, 50% of which were SGA at birth and 50% AGA in New ZealandNot at all, less than 6 months, 6–12 months, >12 monthsStanford
Binet Intelligence Scale, 4th Edition at age 3.5–4 years
Breastfeeding was not significantly related to intelligence scores in the AGA groupExaminer administering the intelligence test, gestation, gender, maternal education, marital status, parental occupation, maternal age, parity and smokingNo difference in IQB
Steer et al92Prospective observational. Breastfeeding data were obtained prospectively9656 children from the Avon Longitudinal Study of Parents and Children cohort, in the UKBreastfeeding within the first month of life vs never breastfeedingWechsler Intelligence Scale for Children, 8 years oldBreastfeeding showed a strong association with full-scale IQ with breastfed children scoring 8 points higher IQ on average in unadjusted analysesMaternal education, paternal social class, low birthweight, preterm gestation, home environment, parenting and genderThe breastfeeding effect attenuated to a 3-point advantage after adjustmentB
Taylor and Wadsworth93Longitudinal population-based cohort. Breastfeeding data were obtained retrospectively13 135 children from The Child Health and Education Study in the UKNever breastfed
Less than 1 month
1–3 months
More than 3 months
English picture vocabulary test (EPVT) adapted from the American Peabody Picture Vocabulary Test, at 5 years of ageChildren breast-fed for three or more months scoring over one-quarter of the SD above the normThe age of the child at testing; the child's sex and birth weight; whether there were older or younger siblings in the home when the study child was five years old; home furnishings and equipment; maternal age at the child's birth; maternal smoking and the social indexBreastfeeding remained a significant influence on EPVT scores, but the difference between the groups was small: +0.12 in the standardised EPVT scoreA
Temboury et al94Prospective cohort229 infants in SpainBreastfed—at least 3 months
Bottle-fed—none or less than 1 month
Bayley's scale at age 18–29 monthsBottle-fed infants had lower IMD scores (index of mental development)Maternal age, education and social class, job, psychosocial risk, number of children, infants’ shyness, tantrum, hyperactivity, gender, birth weight, height, place of birthThe result remained significantC
Thorsdottir et al95Longitudinal cohort85 children in IcelandDuration of exclusive breastfeedingThe Icelandic developmental inventory at age 6 years. Information collected from the mothersDuration of exclusive breastfeeding, in months, was positively related to children's total developmental indexMaternal and paternal education and family income, birth weight, maternal BMITotal developmental index (B=1.07±0.5, p=0.04)C
Tozzi et al96Prospective cohort1403 children originally included in an Italian clinical trial on acellular
Pertussis vaccines
Duration of exclusive breastfeeding both as a continuous variable and as a categorical variable (<6 months, >6 months)An estimated IQ was obtained from scores of the vocabulary, similarities, block design and coding tests at 10–12 years of age
An estimation of IQ was obtained from the scores of the four WISC-R subtests
Scores of only a few neuropsychological tests were affected by exclusive breastfeeding duration: Mean scores on vocabulary, similarities, the Boston naming test and estimated IQ improved with the duration of breastfeeding, whereas performance in one of the subtests for writing praxis decreased with breastfeeding durationSex, birth weight, gestational age, mother's age at birth, type of delivery, family composition, parents’ education, presence of chronic diseases, current prescription of antihistamines or antiepileptic drugs, and the amount of thimerosal to which the children were exposed through vaccinesIn the regression analysis, the score on one subcategory of the California verbal learning test was negatively associated with breastfeeding for longer than 6 months
No difference was detected in any of the other test scores included in the analysis
A
Veena et al97Longitudinal cohort514 children from the Mysore Parthenon birth cohort in south IndiaSix categories from <3 to ≥18 monthsKaufman Assessment Battery at 9-year-old to 10-year-old childrenWithin this cohort, in which prolonged breastfeeding was the norm (90% breastfed ≥6 months), there were no associations between longer duration of breastfeeding and cognitive functionAge, sex, gestation, birth size, maternal age, parity, socioeconomic status, parents’ attained schooling and rural/urban residenceNo difference either unadjusted or after adjustmentB
Whitehouse et al98Longitudinal cohort, breastfeeding data collected prospectively1195 live born children recruited at approximately 18 weeks’ gestation, Western Australian Pregnancy Cohort (Raine) Study(1) Never breastfed,
(2) Breastfed predominantly for <4 months, (3) Breastfed predominantly for 4–6 months
(4) Breastfed predominantly for >6 months
Peabody Picture Vocabulary Test—Revised (PPVT-R) at age 10 years. Raw scores are transformed to standard scores, based around a mean of 100 and an SD of 15Strong positive association between the duration of predominant breastfeeding and PPVT-R at age 10 yearsMaternal age at conception, maternal education, family income and the presence of the biological father in the family home, maternal smoking and alcohol consumption during pregnancy, maternal experience of stressful events during pregnancy, parity, gestational age, child's sex and proportion of optimal birth weight, a measure of the appropriateness of fetal growth, family functioning (MMFAD), Parenting
Scale, language-learning environment
Children who were predominantly breastfed for >6 months had a mean PPVT-R score that was 4.04 points higher than that of children who were never breastfedA
Wigg et al99Longitudinal cohort, breastfeeding data collected prospectively375 children born in Port Pirie, South AustraliaAt 6 month of age: breastfed vs bottle-fed
Children who were breastfed for less than 6 months would have been classified in our analysis as bottle-fed
BSID at age 2, the McCarthy Scales of Children's Abilities age 4 and Wechsler Intelligence Scale for Children at age 7, 11, 13Estimated unadjusted advantages for the breastfed children at ages 2, 4 and 7 years were 5.5 points, 4.6 points and 4.3 points in the MDI, GCI and IQ scores, respectively
At age 11–13 years, the unadjusted advantage for the breastfed children was 3.8 points in IQ
Gender, maternal age at delivery, socioeconomic status, HOME score, maternal IQ, parental smoking habits, birth weight, birth rank, lifetime average blood lead concentration and whether parents were living togetherAdjusting for the covariates diminished the association of the feeding method in infancy with cognitive development.
The covariates contributing most to this attenuating effect were the HOME scores, maternal IQ, socioeconomic status and parental smoking habits
B
Zaini et al100Retrospective cohort1397 children from Selangor Malaysia<6 months
>6 months
Raven's Colored Progressive Matrices at a mean age 9.6 yearsThose who were breastfed less than 6 months performed better (31.01 vs 30.63 of max 36)NoneNoneC
Zhou et al101Prospective cohort302 children born between 1998 and 1999 in Adelaide, AustraliaNot breastfed, breastfed at hospital discharge, less than 6 months, more than 6 monthsStanford-Binet Intelligence Scale at 4 years of ageThere was no association between duration of breastfeeding and childhood IQ in this relatively well-nourished cohort from an industrialised society. Before adjustment, children who were breastfed for at least 6 months had a higher IQ than those who were breastfed for less than 6 monthsBirth order and sex of the child, maternal smoking in pregnancy, parental education, parental occupation and quality of home environmentThere was no association between breastfeeding and childhood IQB
  • BF, breastfeeding; BMI, body mass index; LC-PUFA, long-chain polyunsaturated fatty acids; RCT, randomised controlled trial.