The Benefits of Breastfeeding on Child Intelligence,Behavior,and Executive Function: A Review of Recent Evidence

Abstract

Background:

The effects of breastfeeding on neurodevelopmental outcomes are unclear. Inconsistent findings have been reported and confounding factors make interpretation of studies difficult. The World Health Organization published a systematic review on breastfeeding and intelligence in 2013, demonstrating a positive association with improved performance on intelligence tests. The objective of this review is to explore published literature since 2013 to examine the association between breastfeeding, cognition, executive function, and behavior.

Methods:

Duplicate searches were carried out using Web of Science and OVID for publications between January 2012 and March 2022. Non-English articles and those not correcting for maternal IQ or home environment were excluded.

Results:

Twenty-three studies were included, examining the effects of breastfeeding on cognition (21), executive function (3), and behavior (6). Most studies showed a modest dose-dependent increase in cognitive scores in children who were breastfed, test score differences ranging from 0.19 to 0.96 points per month of breastfeeding comparing any breastfeeding, predominant and exclusive breastfeeding. Four out of six studies showed a positive correlation between breastfeeding and behavior. One out of three studies assessing breastfeeding and executive function showed a positive dose-dependent correlation.

Discussion:

Recent evidence demonstrates that breastfeeding has a small positive effect on IQ in later childhood. Evidence suggesting that breastfeeding is a protective factor in developing conduct disorders and achieving higher executive function is limited. Further research is required. Limitations include potential confounders and recall bias of breastfeeding.

What Is Already Known on This Topic?

There is a positive association between breastfeeding and cognition/IQ.

Confounding factors such as maternal IQ and home environment are important to consider when interpreting study results.

Not breastfeeding can have health implications for the mother and child as well as financial and environmental implications on a wider worldwide scale.

What This Study Adds?

There is a positive association between breastfeeding and conduct disorders.

The correlation between breastfeeding and executive function is less well known.

Recent literature supports the previously shown positive association between breastfeeding and cognition/IQ.

Introduction

The World Health Organization (WHO) recommends exclusive breastfeeding (EBF) for the first 6 months of life, with continued breastfeeding for 2 years and beyond.¹ Breastfeeding rates are improving slowly in the United Kingdom but remain suboptimal. The most recent U.K.-wide infant survey in 2010 demonstrated that 81% of infants received “any” breast milk at birth, but this dropped significantly at 6 and 12 months to 34% and 0.5%, respectively.² England, Scotland, Wales, and Northern Ireland collect data on breastfeeding prevalence independently at the 6- to 8-week check, and the last reports from all four nations in 2016–2017 document that 44.4% (England), 41% (Scotland), 34.2% (Wales), and 28.6% (N Ireland) of infants are at least partially breastfed at 6–8 weeks.^3–5

There are clear short-term benefits of breastfeeding for children, including reduced morbidity and mortality rate from infectious diseases, most notably diarrheal and respiratory infections.⁶ Long-term benefits include a reduction in noncommunicable diseases such as obesity and type 2 diabetes.¹ However, the association between breastfeeding, and particularly EBF, and longer term child development is less clear and challenging to examine. Many of the studies examining breastfeeding and child development are from resource-rich countries and concentrate on outcomes of cognition and IQ. Mothers in these settings who choose to breastfeed are more likely to be from a higher socioeconomic background, have achieved a higher level of education, and provide a stimulating home environment.¹ It has been shown that home stimulation (Home Observation Measurement of the Environment-Short Form score) and maternal IQ scores correlate with breastfeeding duration.⁷

As maternal IQ, maternal education, and stimulation at home are positively associated with a child's cognition, these confounding factors must be accounted for when attempting to establish a link between breastfeeding and improved neurodevelopmental outcomes.¹

In 2013, the WHO published an updated systematic review on the relationship between breastfeeding and intelligence tests, concluding that there was a modest causal effect of breastfeeding on IQ, demonstrating a 3.5-point increase in normalized test scores.¹ Different intelligence tests were used in the studies, but all had a reference mean value of 100 and standard deviation of 15. Of note, the studies included compared two groups according to the method of feeding. Six of the thirteen studies defined this as “ever breastfed” versus “never breastfed,” with the remaining studies quantifying the duration of breastfeeding and/or predominant/EBF.¹ Der et al, identified a 4.69-point difference in IQ in breastfed children, which attenuated to 0.52 points when adjusted for variables including home stimulation and maternal IQ.⁸ Similarly a study by Gibson-Davis and Brooks-Gunn demonstrated a 6.6-point difference in cognitive scores, which attenuated to 1.72 points when corrected for home environment and maternal IQ.⁹

Interestingly, a study by Evenhouse and Reilly involved sibling groups who were fed discordantly. They showed that children who were ever breastfed had on average 1.68 points higher IQ compared with their never breastfed siblings.¹⁰ Most studies have reported on IQ as the outcome, and associations between breastfeeding, executive function, and behavior are less well established. Executive function is the ability to purposely start and complete a goal, problem-solve, and control emotions and impulses during the task. This function emerges throughout childhood into adulthood and is postulated to begin in infancy.⁷

In recent years, there has also been renewed interest in determining whether breastfeeding is protective against the subsequent diagnosis of behavioral disorders such as attention-deficit/hyperactivity disorder (ADHD), conduct disorders, autistic spectrum disorder, and emotional problems. This literature review aims to review the literature over the last 10 years (2012 to March 2022), examining new findings on the association of breastfeeding on IQ, executive function, and behavior.

Methods

Duplicate searches were carried out using Web of Science and OVID. The terms included in the search were “IQ,” “Intelligence,” “Cognition,” “Executive function,” “Emotional development” and “Behavioural development” and “Breastfeeding,” “Breastfed” or “Breast milk.” The limits included English language, and the timing of publication was restricted to 2012 to March 2019. Systematic reviews were further reviewed to check for references. Publications were excluded if the content was not relevant, and studies were included if they documented details of any breastfeeding and a measurable outcome of development. Studies were excluded if they did not correct for maternal IQ and/or home environment or stimulation. We also excluded studies if the patients recruited were predominantly low birth weight or preterm due to differences in expected development.

In March 2022, a further search was carried out using Web of Science and OVID, limits March 2019 to March 2022. The terms included in the search were identical to the above (Fig. 1).

FIG. 1.

Results from online search.

Results

Forty studies were initially identified that aimed to determine if there was an association between breastfeeding and cognition, executive function, or behavior, as shown in Figure 1. Seventeen of these studies were included following exclusions. This literature review was updated in March 2022 and a further 6 studies were identified, bringing the total studies included in this review to 23. Six studies adjusted for maternal IQ and home environment^7,11–15 (Table 3), 10 for maternal IQ only^16–25 (Table 2), and 7 for home environment only^26–32 (Table 1). Twenty-one of the studies were carried out in resource-rich countries^{7,11–14,16,18–32} and two studies in resource-limited countries.^15,17 Twenty-one of the studies assessed cognition,^{11–16,18–32} three assessed executive function,^7,14,15 and six assessed behavior.^{7,13,15,17,20,31}

Table 1.

Summary of Studies Reviewed Adjusted for Home Environment and Maternal Education but Not Maternal IQ

Author (publication year),^Ref. country	Study design	No. in study	Prospective or retrospective collection of breastfed information?	Information on EBF?	Category of feeding	Measure of development (refer to Table 4 for details)	Area assessed	Results	Adjusted result^a	Adjusted for maternal IQ?
Gibbs and Forste (2014),²⁶ United States	Prospective cohort study	7,500	Prospective	No	(1) Predominant—up to 6 months (2). Predominant 3–5 months (3) Not predominant <3 months	Math IRT and reading IRT Age at testing: 4 years	Cognition	Statistically significant improvement in math/verbal scores if predominantly breastfed.	No significant association in fully adjusted models.	No
Huang et al (2014),²⁷ United States	Cohort study	3,129	Retrospective	No	(1) Never breastfed (2) Ever breastfed and (3) Duration breastfed in months up to 12 months	WJ-R Age at testing: 3–17 years	Cognition	No unadjusted results given.	Breastfed increased child's AP score by 3.6 points at age 3 (95% CI), raised the LW score by 3.2 points by age 3, and the PC score by 3.5 points at age 6 (95% CI). One month of additional breastfed raised the AP, LW, and PC score by 0.4, 0.4, and 0.2 points, respectively.	No
Quigley et al (2012),²⁸ United Kingdom	Prospective cohort study	14,819	Prospective	Yes (d)	(1) Never breastfed (2) Exclusive or partial breastfed (<2, 2–3.9 and >4, 6–11 and >12 months)	BAS Age at testing: 5 years	Cognition	The mean naming vocabulary score increased with breastfed duration from 106.5 if never breastfed to 114.2 in children who were breastfed for 12 months at least.	Results were attenuated but there was a 2-point difference at naming vocabulary in term infants breastfed for at least 6 months and a 2-point difference in picture similarities if breastfed >4 months by age 5 years old. Exclusive breastfeeding did not confer any additional points difference.	No
Smithers et al (2012),³⁰ South Australia	Prospective cohort study	7,097	Prospective	No	(1) Ever breastfed (2) Never breastfed	WISC-III Age at testing: 6 and 15 months	Cognition	Breastfeeding at 6 months was associated with +2.54 IQ scores at 8 years.	Breastfed at 6 months was associated with higher IQ scores at 8 years of approximately +1 IQ point difference.	No
Rothstein (2013),²⁹ United States	Cohort study	13,265	Prospective	No	(1) Never breastfed (2) Ever breastfed and (3) Duration breastfed in months up to 6+ months	Data set 1: PIAT-math, reading age 5–6 years Data set 2: math, reading tests in kindergarten Data set 3: WJ LW, AP age 5–6 years	Cognition	Data set 1: a dose–response effect of breastfeeding on partially adjusted scores of 0.026 and 0.074 for reading and math, respectively, for <1 month breastfed and 0.134 and 0.094 for breastfed 6+ months Data set 2: a dose–response effect is evident, math scores of 0.061 for <1 month breastfed increasing to 0.148 for 6 months breastfed. Reading scores 0.08 for <1 month breastfed increasing to 0.116 for 6 months breastfed in partially adjusted results.	Data set 1: results attenuated when corrected for parental score. Reading score no longer statistically significant. Math score attenuated to 0.076-point difference for breastfed +6 months when corrected for parenting score. Data set 2: results attenuated when corrected for parental score. Math scores attenuated to 0.113 for breastfed 6+ months and to 0.084 for reading scores for 6 months breastfed.	No
Amiel Castro et al (2021),³¹ Switzerland	Longitudinal Birth cohort study	11,096	Retrospective	Yes	Exclusive breastfeeding, mixed feeding, exclusive formula feeding	WPPSI 4 years WISC-III 8 years SDQ 4 and 9 years	Cognition behavior	Positive association between breastfeeding and cognition at 4 and 8 years. Negative association with breastfed and hyperactivity/attention deficit, that is, less likely to have diagnosis of ADHD.	EBF (+2.19 points) and mixed feeding (+1.59 points) positively associated with IQ at 8 years. Breastfed negatively associated with hyperactivity/attention deficit at 4 years (EBF) and 9 years (mixed feeding).	No
Wallenborn et al (2021)³² (Switzerland)	Prospective cohort study	2,288	Retrospective	Yes	Exclusive breastfeeding, any breastfed	PRIDI 3 years	Cognition	0.4 SD increase in PRIDI score if EBF compared with mixed feeding.	0.3 SD increase in PRIDI score if EBF compared with mixed feeding in adjusted results.	No

EBF definitions: (a) breast milk only, ±water; (b) breast milk only, no water or other nonbreast milk liquids; (c) predominant breastfed; mainly breastfed but allowed fruit juices/nonmilk liquids; (d) EBF definition not given in article.

Majority adjusted for socioeconomic status, maternal education, income, infant and mother characteristics, paternal factors.

ADHD, attention-deficit/hyperactivity disorder; AP, applied problems; BAS, British Ability Scale test; CI, confidence interval; EBF, exclusive breastfeeding; IRT, item response theory; LW, letter word; PC, passage comprehension; PIAT, Peabody Individual Achievement Test; PRIDI, regional project on child development indicators; SD, standard deviation; SDQ, the Strengths and Difficulties Questionnaire; WISC, Wechsler Intelligence Scale for Children; WJ-R, Woodstock-Johnson Revised; WPPSI, Wechsler Preschool and Primary Scale of Intelligence.

Table 2.

Summary of Studies Reviewed Adjusted for Maternal IQ but Not Home Environment

Author (publication year),^Ref. country	Study design	No. in study	Prospective or retrospective collection of breastfed information?	Information on EBF?	Category of feeding	Measure of development (refer to Table 4 for details)	Area assessed	Results	Adjusted result^a	Adjusted for maternal IQ?
Andres et al (2012),¹⁶ United States	Prospective cohort study	391	Prospective	Yes (a)	Breastfeeding (1) <3 months (2) <6 months (3) >6 months (4) <9 months (5) >12 months	(1) BSID (2) PLS-3 Age at testing: 3, 6, 9, and 12 months	Cognition	Unadjusted results not given	Breastfed infants >IQ scores compared with SF and MF infants. MDI score average difference +2.09 comparing breastfed versus MF/SF. PDI score average 2.69 difference comparing breastfed versus SF. PLS-3 score average difference in breastfed versus MF 3.09 at 3 months, 2.18 at 6 months.	Yes
Girard and Farkas (2019),¹⁷ Chile	Prospective cohort study	3,037	Prospective	No	(1) Never breastfed (2) Breastfed 1–6 months (3) Breastfed 7–12 months (4) Breastfed ≥13 months	CBCL Age at testing: 32–48 months	Behavior	Prepropensity score matching: Breastfed 1–6 months benefit on emotional reactivity (MD −0.81 95% CI) and somatic complaints (MD −0.64 95% CI) Breastfed 7–12 months significant differences if breastfed in emotional reactivity, somatic complaints, withdrawn, attention problems, aggressive scores	Postpropensity score matching: Breastfed 1–6 months benefit on emotional reactivity (MD −1.00 95% CI) and somatic complaints (MD −1.02 95% CI) Breastfed 7–12 months emotional reactivity (MD −0.86 95% CI) and attention problems (MD −0.50 95% CI) Breastfed >13 months; no statistical difference.	Yes
Jedrychowski et al (2012),¹⁸ Poland	Prospective cohort study	468	Prospective	Yes (b)	(1) Never breastfed (2) Combination breast and formula fed (3) Breastfed in number of months	(1) BSID-II (2) WISC-R Age at testing: 1, 2, 3, 6 and 7 years	Cognition	Positive dose-dependent response in breastfed and IQ score. In unadjusted model at age 7 there was an MD in IQ points of +5 comparing breastfed >6 months and complementary feeding	In fully adjusted model children EBF for 3, 4–6 months, >6 months had higher IQ points of +2.1, 2.6, and 3.8, respectively.	Yes
Kim et al (2017),¹⁹ South Korea	Cross-sectional design study	1,712	Retrospective	No	(1) Any breastfeeding (2) Never breastfed	LDES Age at testing: 8–11 years	Cognition	Higher LQ scores in breastfed group 3.2 points difference in unadjusted model	Higher LQ score (speaking, reading, writing, spelling, and maths), 1.95 points increase in ever breastfed versus never breastfed. The effect size was small (0.041–0.117).	Yes
Park et al (2014),²⁰ Korea	Prospective cohort study	874	Retrospective	No	(1) Any breastfeeding (2) Never breastfed	(1) DISC-IV ADHD diagnostic module (2) CBCL (3) KEDI-WISC Age at testing: 8–11 years	Behavior Cognition	Lack of breastfed associated with increased risk of behavioral problems (aOR 3.36, 95% CI) and diagnosis of ADHD (aOR 2.01, 95% CI)	Associations of overall behavioral problems weakened when adjusted for child IQ but remained significant at aOR 2.87 for overall behavioral problems. Association of increased risk of ADHD became insignificant when adjusted for child IQ. Results were similar when adjusted for maternal IQ. Cognition 4.07 additional IQ points any breastfeeding versus never breastfed.
Sajjad et al (2015),²⁵ Rotterdam	Prospective cohort study	3,761	Prospective	Yes (a)	(1) Never(2) Partial for <4 months(3) Exclusive for >4 months (infants EBF >6 months were included in category 3 as they were such a small group)	Dutch nonverbal IQ test (Snijders-Ooomen nonverbal intelligence test)Age at testing: 6 years	Cognition	+4.21 IQ points EBF >4 months and +2.53 IQ points if partial breastfed 4 months compared with never breastfed+4.79 IQ points if partial breastfed 6–10 months compared with children who were never breastfed	Results attenuated when fully adjusted including maternal IQ with large p-value, not statistically significant.	Yes
Guzzardi et al (2020),²² Italy	Prospective birth cohort study	90	Retrospective	Yes	Exclusive breastfeeding and nonexclusive feeding	GMDSAge at testing: 6, 12, 18, 24 and 36 months	Cognition	Higher scores in hearing and language development at 6 months in boys and girls and locomotor skills at 36 months in girls only	In model adjusted for maternal IQ higher scores in hearing and language development at 6 months only (p = 0.046)	Yes
Bellando et al (2020),²¹ United States	Longitudinal cohort study	504	Retrospective	No	Breastfed, MF, soy protein-based formula fed (SF)	BSID-2PLS-33, 12, 24 monthsRIAS48 and 60 months	Cognition	Increase in IQ and language scores in breastfed children compared to MF and SF	Increase in IQ scores at 48 months if breastfed (+3.8 and 5 points) compared to MF and SF. breastfed children had higher language scores (∼6 points) compared with MF/SF at 36 and 48 months.	Yes
Strøm et al (2019),²⁴ Denmark	Prospective cohort study	1,782	Retrospective	No	Breastfed <1 month, breastfed >2–3, 4–6, 7–9, >10 months	WPPSI-RAge 5	Cognition	Increase in IQ in children breastfed >1 month	Compared with children breastfed <1 month children breastfed for 2–3, 4–6, 7–9, >10 months had +3.06, 2.03, 3.53, and 3.28 points higher IQ. No dose–response identified.	Yes
Sobik et al (2021),²³ United States	Prospective cohort study	600	Retrospective	No	Breastfed, MF, soy formula	WPPSI-IIIPLS-3Age 72 months	Cognition	No significant difference in intelligence between the feeding groups	No significant difference in intelligence between the feeding groups.	Yes

Majority adjusted for socioeconomic status, maternal education, income, infant and mother characteristics, paternal factors.

ADHD, attention-deficit/hyperactivity disorder; aOR, adjusted odds ratio; BSID, Bayley Scale of Infant Development; CBCL, Child Behavior Checklist; CI, confidence interval; DISC-IV, Diagnostic Interview Schedule for Children Version IV; EBF, exclusive breastfeeding; GMDS, Griffiths Mental Developmental Scale; KEDI-WISC, Korean Educational Development Institutes Wechsler Intelligence Scale for Children; LDES, Learning Disability Evaluation Scale; LQ, learning quotient; MD, mean difference; MDI, Mental Development Index; MF, cow's milk formula; PDI, Psychomotor Development Index; PLS-3, Preschool Language Scale 3; RIAS, Reynolds Intellectual Assessment Scales; SF, soya formula; WISC-R, Wechsler Intelligence Scale for Children-Revised; WPPSI-R, Wechsler Preschool and Primary Scale of Intelligence-Revised.

Table 3.

Summary of Studies Reviewed Adjusted for Home Environment and Maternal IQ

Author (publication year),^Ref. country	Study design	No. in study	Prospective or retrospective collection of breastfed information?	Information on EBF?	Category of feeding	Measure of development (refer to Table 4 for details)	Area assessed	Results	Adjusted result^a	Adjusted for maternal IQ and home environment
Belfort et al (2013),¹¹ United States	Prospective cohort study	1,312	Prospective	Yes (a)	(1) Ever breastfed(2) EBF to 6 months	(1) PPVT-III(2) WRAVMA(3) KBIT-II(4) WRAMLAge at testing: 3 and 7 years	Cognition	EBF and any breastfeeding were positively associated with cognitive scores. In model only adjusted for child age/sex PPVT-III score (age 3), KBIT-II verbal and nonverbal scores (age 7) were 0.58, 0.96, and 0.65 points higher, respectively, for each month of any breastfed	Results remained significant, although attenuated when demographic variables, HOME-SF score, and maternal IQ accounted for. PPVT-III (age 3) and KBIT-II verbal/nonverbal (age 7) scores were 0.21, 0.35, and 0.29 points higher for each month breastfed and 0.5, 0.8, and 0.58 for each month exclusively breastfed compared with never breastfed	Yes
Belfort et al (2016),⁷ United States	Prospective cohort study	1,037	Prospective	Yes (a)	(1) Any breastfed(2) EBF at 6 months(3) What age weaned off breastfed	(1) BRIEF(2) SDQAge at testing: mean age 7.7 years	Executive function, behavior	Infants EBF scored 0.28 BRIEF points less per month breastfed (fewer metacognition problems)	BRIEF score +0.1 higher per month breastfed and +0.06 higher SDQ score indicating more problems if breastfed for longer duration (against the hypothesis)	Yes
Boucher et al (2017),¹³ Spain	Prospective cohort study	2,080	Prospective	Yes (b, c)	(1) Any breastfed(2) Predominant breastfed(3) EBF	(1) MSCA(2) K-CPT(3) ADHD-DSM-IV(4) CASTAge at testing: mean age 4.9 years	Cognition, behavior	MSCA score; 0.26 extra points per month of any breastfed versus never breastfed, 0.64 points extra per month of predominant breastfed and 0.69 points per month if EBF compared with never breastfed	MSCA GCI score; 0.19 extra points per month of any breastfed versus never breastfed, 0.37 extra points per month of predominant breastfed and 0.48 points if EBF versus never breastfed. CAST score; 0.04-point decrease in CAST score per month of any breastfed compared with never breastfed	Yes
Boutwell et al (2018),¹² United States	Prospective cohort study	1,526	Prospective	No	(1) Never breastfed(2) Breastfed <1 month(3) Breastfed <6 months(4) Breastfed >6 months	WJ-R testsAge at testing: third grade, fifth grade, and age 15	Cognition	Unadjusted results not available	Any amount of breastfeeding associated with higher cognitive scores at grade 3 (b = 0.467, p = .01.)	Yes
Julvez et al (2014),¹⁴ Spain	Prospective cohort study	434	Prospective	Yes (c)	(1) Never(2) Short term <4 months(3) Long term 4–6 months(4) Very long term >6 months	MSCAAge at testing: 4 years	Cognition, executive function	(1) Cognition; +9 increase in MSCA score from never breastfed to >EBF 6 months(2) Executive function scores +9 point difference between never breastfed and EBF >6 months	(1) Cognition; 2.9, 2.7, and 7.3 increase in MSCA points at 4 years if EBF ≤4, 4–6, and >6 months compared with never breastfed(2) Executive function; 2.3, 3.1, and 6.9 additional points in the MSCA subsets at 4 years if EBF ≤4, 4–6, and >6 months compared with never breastfed	Yes
Rochat et al (2016),¹⁵ South Africa	Non-randomised prospective intervention cohort study	906	Prospective	Yes (b, c)	(1) EBF 0–1 month(2) EBF 2–5 months(3) EBF >6 months	(1) KABC-II(2) Developmental neuropsychological assessment(3) Parent-reported CBCLAge at testing: 7–11 years	Cognition, behavior, executive function	EBF for 6 months compared with <1 month was half as likely to score above the mean for conduct disorders (aOR 0.44 with CI 0.3–0.7)	Results remained significant following adjustment of confounders	Yes

Majority adjusted for socioeconomic status, maternal education, income, infant and mother characteristics, paternal factors.

ADHD, attention-deficit/hyperactivity disorder; aOR, adjusted odds ratio; BRIEF, Behavior Rating Inventory of Executive function; CAST, Childhood Autism Spectrum Test; CBCL, Child Behavior Checklist; GCI, General Cognitive Index; EBF, exclusive breastfeeding; HOME-SF, Home Observation Measurement of the Environment-Short Form; KABC-II, Kaufman Assessment Battery for Children-2nd edition; KBIT-II, Kaufman Brief Intelligence Test, 2nd edition; K-CPT, Conners' Kiddie Continuous Performance Test; MSCA, McCarthy Scales of Children's Abilities; PPVT-III, Peabody Picture Vocabulary Test 3rd edition; SDQ, the Strengths and Difficulties Questionnaire; WJ-R, Woodstock-Johnson Revised; WRAML, Wide Range Assessment of Memory and Learning; WRAVMA, Wide Range Assessment of Visual Motor Abilities.

All the studies included infants who were breastfed either exclusively, predominantly, or partially, although not all specified the exact pattern of breastfeeding. Details of the definitions used by the studies are found in Tables 1 –3, and the range of assessment tools is found in Table 4.

Table 4.

Assessment Tools Used in the Study Assessment

Assessment tool	Full name	Information on assessment tool
IRT-math	Item response theory-math	Cognition; assesses ability to understand size/quantity/matching/counting/numbers/ordering.
IRT-reading	Item response theory-reading	Cognition; assesses ability to read including phonology/letters/words.
WJ-R	Woodstock-Johnson Revised Tests of Achievement	Cognition; A standardised measure of a childs cognitive ability. LW identification test and the AP test on children who were >3 and the PC test on children who were >6 in all three waves.
BAS	British Ability Scale Test	Cognition; Assesses children's cognitive function.
WISC	Wechsler Intelligence Scale for Children	Cognition; Measure of memory.
PIAT-R	Peabody Individual Achievement Test—Reading Recognition	Cognition; Measures academic achievement in reading.
PIAT-M	Peabody Individual Achievement Test—Math Ability	Cognition; Measures academic achievement in maths.
BSID	Bayley Scale of Infant Development	Cognition; Assesses mental and psychomotor development giving the test subject an MDI score and a PDI score.
PLS-3	Preschool Language Scale 3	Cognition; Assesses expressive communication and auditory comprehension skills.
CBCL	Child Behavior Checklist	Behavior; Child emotional and behavioral functioning assessed using a parent-reported checklist.
WISC-R	Wechsler Intelligence Scale for Children	Cognition; Measure of memory.
LDES	Learning Disability Evaluation Scale	Cognition; Evaluates learning skills and calculates LQ.
DCIS-IV ADHD diagnostic module	Diagnostic Interview Schedule for Children Version IV ADHD diagnostic module	Behavior; Assesses ADHD symptoms.
KEDI-WISC	Korean Educational Development Institutes Wechsler Intelligence Scale for Children	Cognition; Assesses cognition.
Snijders-Ooomen nonverbal intelligence test	Dutch nonverbal intelligence test	Cognition; Assesses cognition.
PPVT-III	Peabody Picture Vocabulary Test 3rd edition	Cognition; Measures hearing and receptive language.
WRAVMA	Wide Range Assessment of Visual Motor Abilities	Cognition; Assesses fine motor, visual spatial, and visual motor skills.
KBIT-II	Kaufman Brief Intelligence Test, 2nd edition	Cognition; Measures verbal and nonverbal intelligence—a measure of IQ.
WRAML	Wide Range Assessment of Memory and Learning	Cognition; Assesses visual memory.
BRIEF	The Behavior Rating Inventory of Executive Function	Executive function; Assessment tool on executive function; higher scores represent worse executive function.
SDQ	The Strengths and Difficulties Questionnaire	Behavior; A behavioral screening questionnaire valid for completion by parents or teachers of 4- to 16-year olds. Higher scores indicate greater difficulty except for prosocial subscale.
MSCA	McCarthy Scales of Children's Abilities	Cognition; MSCA generates a general cognitive index. MSCA (using a Spanish standardized version); tests across six domains (general cognition, verbal, quantitative, memory, perceptive performance, and motor function). All tests were carried out by one specially trained psychologist.
K-CPT	Conners' Kiddie Continuous Performance Test	Behavior; K-CPT tests attention function.
ADHD-DSM-IV	DSM-ADHD symptoms form list	Behavior; ADHD-DSM-IV completed by teacher; assesses ADHD symptoms.
CAST	The Childhood Autism Spectrum Test	Behavior; CAST filled in by parents aka childhood Asperger's test.
KABC-II	Kaufman Assessment Battery for Children-2nd edition	Cognition; Cognitive function is assessed by four subscales; sequential processing, simultaneous processing, learning ability, and planning.
PRIDI	Regional Project on Child Development Indicators	PRIDI is a method of collecting data on overall development of children aged 2–5 in Latin America including cognition, language, social, emotional, and motor development.
RIAS	Reynolds Intellectual Assessment Scales	Measures general cognitive ability, verbal intelligence, and nonverbal intelligence.
WPPSI	Wechsler Preschool and Primary Scale of Intelligence	Intelligence test for children; verbal, performance, and full-scale IQ.
GMDS	Griffiths Mental Developmental Scale	Measures rate of development of infants and young children in 6 domains; locomotor, personal-social, hearing and language, eye and hand co-ordination, performance, and practical reasoning domain.
Developmental neuropsychological assessment	Developmental neuropsychological assessment	Executive function; Assesses child's executive function-3 subsets of animal sorting, auditory attention, and response set.

ADHD, attention-deficit/hyperactivity disorder; AP, applied problems; CAST, Childhood Autism Spectrum Test; K-CPT, Conners' Kiddie Continuous Performance Test; LQ, learning quotient; MDI, Mental Development Index; MSCA, McCarthy Scales of Children's Abilities; PC, passage comprehension; PDI, Psychomotor Development Index; WISC-R, Wechsler Intelligence Scale for Children-Revised.

Long-term effects of breastfeeding on cognitive function

Twenty-one of the articles assessed the effects of breastfeeding on cognition, five of which adjusted for both maternal IQ and home environment^11–15 (Table 3), nine for maternal IQ only^16,18–25 (Table 2), and seven for home environment only^26–32 (Table 1). Of the 21 studies, 17 demonstrated a modest increase in cognitive scores in children who were breastfed.^{11–14,16,18–22,24,27–32} Two studies used the McCarthy Scales of Children's Abilities (MSCA) assessment tool, both demonstrating a positive dose-dependent effect between breastfeeding and MSCA test scores of between 2.9 and 7.3 depending on the length of breastfeeding.^13,14 Studies comparing EBF and partial breastfeeding demonstrated a dose effect with exclusively breastfed infants showing higher cognitive scores per month of EBF compared with infants who were partially breastfed. The test score differences ranged from 0.19 to 0.96 points per month of breastfeeding comparing any breastfeeding, predominant and EBF.^12,13,27

Boutwell et al showed that higher cognitive scores at third grade, fifth grade, and age 15 years were evident if the infants had been breastfed for more than 6 months compared with <1 month and between 1 and 6 months.¹² However, 2 of the 15 studies did not show a statistical difference when adjusted for confounders.^25,26 A study from South Africa was the only article that assessed the effects of breastfeeding on cognition in a resource-limited setting. Overall, there was no benefit to IQ in children who were breastfed. Breastfeeding for 2–5 months was weakly associated with an increase in IQ in comparison to those who were breastfed <1 month.¹⁵

Long-term effects of breastfeeding on executive function

Three studies assessed the association between breastfeeding and executive function.^11,14,15 An American study hypothesized that longer duration of breastfeeding would be associated with improved executive function, assessed using the Behavior Rating Inventory of Executive function (BRIEF) where lower metacognition scores indicate higher executive function. Initial results demonstrated that a longer duration of EBF resulted in lower metacognition scores, that is, better executive function (−0.28 points per month breastfed). However, in the fully adjusted results, breastfeeding was associated with higher metacognition scores, that is, longer duration breastfeeding was associated with a poorer executive function score in children aged 7–10 years.¹¹ Similarly, a study from rural South Africa, testing children ages 7–11 years, did not demonstrate a significant association between improved executive function and longer duration of breastfeeding.¹⁵

Conversely, a prospective cohort study from Spain demonstrated a significant improvement in executive function scores (tested at 4 years of age) in infants fully breastfed compared with those who were never breastfed, and this finding was dose dependent.¹⁴

Long-term effects of breastfeeding on behavior

Six studies aimed to establish if there is a link between breastfeeding and behavioral outcomes and demonstrated conflicting results.^{7,13,15,17,20,31} Four showed a positive correlation,^15,17,20,31 two of which were conducted in resource-limited countries.^15,17 A Korean study demonstrated that not breastfeeding resulted in increased risk of internalizing and externalizing behavioral problems by an adjusted odds ratio of 2.31 and 1.96, respectively.²⁰ Of the two studies in resource-limited settings, Rochat et al describe a rural South African cohort study exploring the association between duration of EBF and behavior, including the six diagnostic mental (DSM) disorders: affective, anxious, somatic, ADHD, oppositional, and conduct disorders. When assessing conduct, EBF was significantly associated with lower scores on the parent-reported Child Behavior Checklist (CBCL), indicating fewer conduct problems in those who were EBF for 6 months compared with those EBF for <1 month. None of the other five DSM disorders showed statistically significant results.¹⁵

A further study in Chile demonstrated that infants breastfed for 0–6 months scored lower for emotional reactivity on the parent-reported CBCL compared with infants never breastfed. They found a dose-dependent relationship up to 13 months, after which the results were not statistically significant. Somatic complaints were less common among the groups breastfed for 1–6 months.¹⁷

Two studies assessing the effect of breastfeeding on behavior demonstrated negative effects. Belfort et al showed that infants in the United States who were breastfed had an increased Strengths and Difficulties Questionnaire (SDQ) score, indicating more behavioral problems.⁷ Similarly a study by Boucher et al showed that Spanish children aged 7 years had slower reaction times on the Conners' Kiddie Continuous Performance Test (K-CPT) assessment tool for each additional month of breastfeeding, indicating they had more inattention. It was postulated that the children who scored higher on the K-CPT had slower reaction times, which could represent better impulse control. The same study demonstrated a positive correlation with breastfeeding observing that breastfed children had fewer autistic traits.¹³

Discussion

An increase in IQ; does it matter?

In line with the previous body of research, most studies in our review demonstrate a positive association between breastfeeding and IQ that appears to be dose dependent, with longer durations of breastfeeding associated with more gains in IQ. However, the differences in IQ between breastfed and nonbreastfed infants remain small, 0.19–0.96 additional test points per month breastfed,^11,13,27 or 2–7.3 additional test points overall.^{13,14,16,18,27,28} Whether or not this small difference in IQ has an impact on the individual is debated. It has been proposed that the benefit of breastfeeding on cognitive function does not end in childhood.

Two unique studies, not included in this literature review, tested participants in adult life and demonstrated that infants who were breastfed had higher cognitive scores much later in life at 67 years³³ and 30 years.³⁴ Evidence that the neurocognitive benefits of breastfeeding reach into adulthood is exciting and could potentially result in higher earnings and economic wealth in later life. A modest but significant increase in IQ points at the population level could have large economic results. Horta et al discuss the impact of breastfeeding on the earning ability. Children who had been breastfed for 12 months had a higher income (an additional 341 Brazilian reals; monthly income approximately one-third higher than the average wage) at age 30 compared with those who were breastfed for <1 month.^34,35 The studies were not included in our review as they did not meet the selection criteria.

Of note, a U.K.-based UNICEF report states that if 1% of women in the United Kingdom who never breastfed were to opt to breastfeed, this could result in £278 million in economic productivity of each birth cohort in the United Kingdom. They also postulated that a 2-point increase in IQ points could result in an increase in lifetime earnings of £35,000–72,000.³⁶ The population implications of this are huge. Hafstead and Lutter explore the relationship between breastfeeding, higher IQ, and potential monetary gains. They estimate that the individual benefit of breastfeeding is an increase in lifetime earnings of $20,000. At a population level, they postulate that if half of the U.S.-born infants were breastfed for 12 months, it would equate to an increase of $40 billion annual increase in future earnings.³⁷

Reverse hypothesis

It has been hypothesized that some children may benefit from breastfeeding more than others. “Differential susceptibility” hypotheses suggest that some children are more vulnerable to the effects of negative rearing. Negative rearing is described as a negative parenting experience, that is, an environment that is not nurturing. These children may benefit more from an intervention such as breastfeeding promotion.¹⁵ While there is limited literature on the differential susceptibility hypothesis and how it relates to breastfeeding, Koh demonstrated a positive association between breastfeeding and IQ and found that breastfeeding has a more positive effect on children with lower cognitive potential compared with children with high cognitive scores.³⁸ Breastfeeding promotion is a relatively inexpensive health improvement strategy that has the potential to increase cognition and thus the future earnings of children involved, with enormous potential impact in resource-limited settings.

Confounders

The role of confounders remains problematic. In our review, the majority of studies that accounted for maternal IQ demonstrated a positive effect of breastfeeding on IQ. Results were typically attenuated following adjustment but maintained statistical significance.^{13,14,18–20} It has been shown that stimulation at home is associated with better cognitive and language skills as is being from a more affluent background.^35,39 In our review, the majority of articles that accounted for home environment had results that were attenuated but remained significant after adjusting for covariates.^{11–15,27–30} Future research focusing on sibling groups fed discordantly could reduce the selection bias and the impact of confounding factors.

Breastfeeding and behavior

A relatively new area of research is exploring the links between breastfeeding and behavior, with only five studies identified in our review. Surprising results were evident in a cohort analysis that demonstrated an increase in SDQ score (correlating to worse behavior) in infants who were breastfed for longer in the fully adjusted models.⁷ The cause for this is unclear, however, the cohort included women of high socioeconomic status and did not represent the general population. Conversely, a South African study concluded that EBF was associated with less conduct disorders and was weakly associated with improved cognition in boys only.¹⁵ A separate study assessing ADHD tendencies showed a negative association between attention score and breastfeeding duration.¹³

Breastfeeding and executive function

This review identified three studies that assessed executive function and breastfeeding.^7,14,15 It was expected that the dose-dependent positive relationship between breastfeeding and improved executive function demonstrated by Julvez et al would also be demonstrated in other studies. It was therefore surprising that Belfort et al demonstrated a negative correlation, and the study by Rochat et al showed no benefit. Executive function evolves throughout childhood and into adult life and it could be that testing in childhood is underestimating the effects that may become more apparent over time. Studies following cohorts into adulthood are currently limited, but may provide further useful findings.⁷

Methodology of recent studies

Limitations of this review include confounders and recall bias. In the currently utilized research models of cohort studies, it is truly impossible to eliminate residual confounders. However, there are ethical issues with randomized controlled trials where infants are randomized to breast or artificial feeding. This could be overcome by randomizing women to receive standard breastfeeding support or a higher level of support.^40,41 While some studies specify the pattern of breastfeeding (EBF, predominant, or partial breastfeeding), many state only “any” or “never” breastfed. It is important that future studies use universally accepted definitions of breastfeeding patterns, to allow more accurate comparisons.

Recall of breastfeeding exclusivity and duration is subject to bias and women may over or underestimate the length of breastfeeding. A study examining maternal recall of the duration of EBF found that 48 h recall did not accurately reflect breastfeeding practices since birth, and longer term recall of EBF was even more inaccurate. The authors recommended collecting data prospectively with a maximum of 7-day recall.⁴²

A meta-analysis review was out of the scope of this review. The studies examining breastfeeding and cognition and child behavior are diverse with different measures and diverse outcomes, making a systematic or literature review more appropriate.

Summary

The current review demonstrates that breastfeeding is likely to have a positive effect on IQ in later childhood although the magnitude of this is uncertain. There is also limited evidence suggestion that breastfeeding is a protective factor in developing later conduct disorders and achieving higher executive function, providing an exciting new area of research. The role of confounders in all these areas is problematic. Potential research could explore groups of siblings who have been fed discordantly, limiting the role of confounders, or explore outcomes in children where mothers have been randomized to different breastfeeding promotion interventions. Future research should carefully document the duration and pattern of breastfeeding, with attention paid to the length of recall of breastfeeding practices. Breastfeeding has numerous benefits for children, their mothers, and the society. Working to establish further long-term benefits of breastfeeding is warranted and an exciting area of research.

Footnotes

Authors' Contributions

C.M.: Conceptualization, methodology, validation, formal analysis, investigation, writing—original draft, writing—review and editing, and project administration. R.B.: Conceptualization, methodology, validation, formal analysis, investigation, writing—review and editing, project administration, and supervision.

Disclosure Statement

There is no conflict of interest to declare.

Funding Information

There are no sources of funding to declare.

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