Intelligence and breast feeding

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Studies often find higher IQ in children and adults who were breastfed.[1][2] 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.

Studies examining whether breastfeeding in infants is associated with higher intelligence later in life include:

• Horwood, Darlow and Mogridge (2001) tested the intelligence quotient (IQ) scores of 280 low birthweight children at seven or eight years of age. Those who were breastfed for more than eight months had verbal IQ scores 6 points higher (which was significantly higher) than comparable children breastfed for less time. They concluded "These findings add to a growing body of evidence to suggest that breast milk feeding may have small long term benefits for child cognitive development."
• A 2005 study using data on 2,734 sibling pairs from the National Longitudinal Study of Adolescent Health "provide[d] persuasive evidence of a causal connection between breastfeeding and intelligence."
• In "the largest randomized trial ever conducted in the area of human lactation," between 1996 and 1997 maternity hospitals and polyclinics in Belarus were randomized to receive or not receive breastfeeding promotion modeled on the Baby Friendly Hospital Initiative. Of 13,889 infants born at these hospitals and polyclinics and followed up in 2002-2005, those who had been born in hospitals and polyclinics receiving breastfeeding promotion had IQs that were 2.9-7.5 points higher (which was significantly higher). Since (among other reasons) a randomized trial should control for maternal IQ, the authors concluded in a 2008 paper that the data "provide strong evidence that prolonged and exclusive breastfeeding improves children's cognitive development."
• 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.
• The 2007 review for the AHRQ found "no relationship between breastfeeding in term infants and cognitive performance."
• The 2007 review for the WHO concluded "Subjects who were breastfed experienced... higher performance in intelligence tests."

• 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 .. FADS2 affects the metabolism of polyunsaturated fatty acids found in human breast milk, such as docosahexaenoic acid and arachidonic acid, which are known to be linked to early brain development. The researchers were quoted as saying "Our findings support the idea that the nutritional content of breast milk accounts for the differences seen in human IQ. But it's not a simple all-or-none connection: it depends to some extent on the genetic makeup of each infant." The researchers wrote "further investigation to replicate and explain this specific gene–environment interaction is warranted."