A new study shows that the intellectual boost associated with breast milk is only attained if a child has inherited one of two versions of a specific gene. The NIMH funded research is among the first to provide evidence of a specific genetic-environment interaction involved in complex mental functioning.
NIMH grantees Avshalom Caspi, Ph.D, and Terrie Moffitt, Ph.D.,
Breastfed children are thought to have a 6-7-point IQ advantage over non-breastfed children, likely traceable to certain fatty acids found in human milk and important for brain development, according to the researchers.
Caspi and colleagues suspected that IQ hinges, in part, on differences in metabolizing these fatty acids that could be influenced by variability in a gene. To find out if such a gene-environment interaction is involved, they first identified a likely candidate gene, FADS2, which codes for an enzyme known to play a key role in fatty acid production.
Then they studied how two versions of this gene, called C and G, affected IQ in 1000 children who grew up in New Zealand and 2200 children who grew up in Britain.
They confirmed that children who had been breastfed had a 6.8-point IQ advantage, but only if the children had at least one copy of the C version.
Children with two copies of the G version, 10 percent of those studied, neither gained nor suffered intellectually from breast feeding. The study adds to evidence that genes may be influenced by environmental factors to shape IQ.
Caspi A, Williams B, Kim-Cohen J, Craig IW, Milne BJ, Poulton R, Schalkwyk LC, Taylor A, Werts H, Moffitt TE. Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism. Proc Natl Acad Sci U S A. 2007 Nov 5; [Epub ahead of print] PMID 17984066