Impact of breast milk on IQ, brain size and white matter development (2010)
This study does not control for maternal IQ or socio-economic status. Later studies show that much of the link between breastfeeding and cognitive development is due to confounding effects (in particular, higher SES mothers are more likely to breastfeed): <a href="http:&#x2F;&#x2F;bmjopen.bmj.com&#x2F;content&#x2F;3&#x2F;8&#x2F;e003259" rel="nofollow">http:&#x2F;&#x2F;bmjopen.bmj.com&#x2F;content&#x2F;3&#x2F;8&#x2F;e003259</a><p>&gt; Conclusions Much of the reported effect of breastfeeding on child neurodevelopment is due to confounding. It is unlikely that additional work will change the current synthesis. Future studies should attempt to rigorously control for all important confounders. Alternatively, study designs using sibling cohorts discordant for breastfeeding may yield more robust conclusions.<p>See also: <a href="http:&#x2F;&#x2F;pediatrics.aappublications.org&#x2F;content&#x2F;early&#x2F;2017&#x2F;03&#x2F;23&#x2F;peds.2016-1848" rel="nofollow">http:&#x2F;&#x2F;pediatrics.aappublications.org&#x2F;content&#x2F;early&#x2F;2017&#x2F;03&#x2F;...</a><p>&gt; RESULTS: Before matching, breastfeeding was associated with better development on almost every outcome. After matching and adjustment for multiple testing, only 1 of the 13 outcomes remained statistically significant: children’s hyperactivity (difference score, –0.84; 95% confidence interval, –1.33 to –0.35) at age 3 years for children who were breastfed for at least 6 months. No statistically significant differences were observed postmatching on any outcome at age 5 years.<p>The linked study also yields some odd results:<p>&gt;  In the total group �M correlated significantly with Verbal IQ (VIQ); in boys, with all IQ scores, TBV and WMV. VIQ was, in turn, correlated with WMV and, in boys only, additionally with TBV. <i>No significant relationships were seen in girls</i> or with grey matter.<p>A meta-study that adjusted for maternal IQ only (but not socioeconomic status, which independently correlates with higher rates of breastfeeding) found a very small effect on IQ: <a href="https:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;26211556" rel="nofollow">https:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;26211556</a><p>&gt; We included 17 studies with 18 estimates of the relationship between breastfeeding and performance in intelligence tests. In a random-effects model, breastfed subjects achieved a higher IQ [mean difference: 3.44 points (95% confidence interval: 2.30; 4.58)]. We found no evidence of publication bias. <i>Studies that controlled for maternal IQ showed a smaller benefit from breastfeeding [mean difference 2.62 points</i> (95% confidence interval: 1.25; 3.98)]. In the meta-regression, none of the study characteristics explained the heterogeneity among the studies.