Breastfeeding and intelligence

Studies often find higher IQ in children and adults who were breastfed. It has also been proposed that the omega-3 fatty acids that are found in high doses in breast milk, and that are known to be essential constituents of brain tissues, could at least partially account for an increase in IQ.

Recently, however, the longstanding belief that breastfeeding causes an increase in the IQ of offspring was challenged in a 2006 paper published in the British Medical Journal. The results indicated that mother's IQ, not breastfeeding, explained the differences in the IQ scores of offspring measured between ages 5 and 14. The results of this study argued that prior studies had not controlled for the mother's IQ. Since mother's IQ was predictive of whether a child was breastfed, the study concluded that "breast feeding [itself] has little or no effect on intelligence in children." Instead, it was the mother's IQ that had a significant correlation with the IQ of her offspring, whether the offspring was breastfed or was not breastfed. Another study found that breastfeeding had a positive effect on cognitive development at 24 months of age even after controlling for parental IQ.

A potential resolution to these different interpretations was proposed in a study showing that breastfeeding was linked to raised IQ (as much as 7 points when not controlling for maternal IQ) if the infants had an SNP coding for a "C" rather than G base within the FADS2 gene. Those with the "G" version showed no IQ advantage, suggesting a biochemical interaction of child's genes on the effect of breast feeding. Other studies have failed to replicate any correlation between the FADS2 gene, breastfeeding and IQ, while others show a negative effect on IQ when combining bottledfeeding, and the "G" version of FADS2.