Two studies of children in Britain and New Zealand have found that the known link between higher IQ and being breast fed as a baby may be down to a gene variant likely to be present in 90 per cent of the population.

The two studies are published in one paper in the November 5th issue of the Proceedings of the National Academy of Sciences and are the work of Dr Terrie Moffitt a professor of psychological and brain sciences in Duke University's Institute for Genome Sciences and Policy, Durham, North Carolina, USA, and her husband, Dr Avshalom Caspi professor of personality development, Institute of Psychiatry, King's College London, UK, and colleagues.

For some time, scientists have believed that the fatty acids in breast milk might explain why children who were breast fed as babies tend to get higher scores in IQ tests than children who were not.

In these studies, Moffitt, Caspi and colleagues showed that the link betwee breastfeeding and IQ involves a variant of a gene called FADS2 which partly controls the fatty acid pathways.

In the two studies of more than 3,000 children in Britain and New Zealand, the researchers showed that breastfeeding raised IQ by an average of nearly 7 points if the children concerned also had the FADS2 variant.

The analysis ruled out factors such as fetal growth in the uterus, social class, and maternal intelligence, as well as any influence the maternal genes may have had on breastfeeding and breast milk.

Moffitt said that:

"There has been some criticism of earlier studies about breastfeeding and IQ that they didn't control for socioeconomic status, or the mother's IQ or other factors, but our findings take an end-run around those arguments by showing the physiological mechanism that accounts for the difference."

Moffitt, Caspi and colleagues found that it is not a case of nature or nurture, but an alliance of the two that is at work here. It is the way the gene interacts with the child's environmental influences that results in the IQ boost, they said.

The children with at least one copy of the C variant of the gene, which occurred in 90 per cent of the two study groups, scored higher IQ if they were breastfed. But there was no link between breastfeeding and IQ for the other 10 per cent of children, who had the G variant of FADS2.

The researchers decided to focus on FADS2 because it codes for an enzyme that converts fatty acid from digested food into two polyunsaturated fatty acids DHA (docosahexaenoic acid) and AA (arachidonic acid) that collect in the brain during the early months of a baby's life.

Makers of infant formula have been adding DHA and AA fatty acids to their products since this discovery ten years ago. However, the children in the British and New Zealand studies were born in 1972-73 and 1994-95 respectively, before manufacturers started adding fatty acids to infant formula.

Laboratory tests on rats and primates have confirmed that fatty acid supplementation during the first few months of life is linked to higher levels of brain DHA and higher scores in tests of memory, learning and problem solving. As far as we know, there have been no such tests on humans.

The researchers concluded that the research shows that:

"Environmental exposures can be used to uncover novel candidate genes in complex phenotypes. It also shows that genes may work via the environment to shape the IQ, helping to close the nature versus nurture debate."

Stressing the team's interest in both the nature and the nurture side of the science, Moffitt said that:

"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."

"We're more interested in proving to the psychiatric community that genes usually have a physiological effect. When looking at depression or intelligence, the key bit that's often left out here is the environmental effects," she added.

"Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism."
Avshalom Caspi, Benjamin Williams, Julia Kim-Cohen, Ian W. Craig, Barry J. Milne, Richie Poulton, Leonard C. Schalkwyk, Alan Taylor, Helen Werts, and Terrie E. Moffitt.
Proc. Natl. Acad. Sci. published November 5, 2007
10.1073/pnas.0704292104

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Written by: Catharine Paddock