Published online 5 November 2007 | Nature | doi:10.1038/news.2007.217

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The gene that turns breast-milk into brain food

Not all children can harness the full goodness of their mother’s milk.

Breast is best: mother's milk helps some babies to get an intelligence boost.Getty

Does breast-feeding a child boost its brain development and raise its intelligence? Only if the child carries a version of a gene that can harness the goodness of breast-milk, say researchers.

The results add to the ‘nature versus nurture’ debate over intelligence, by showing how the two effects can interact.

The question of whether people are born intelligent or made intelligent by their environment has been debated for decades. Research with identical twins separated at birth has shown that both genetics and rearing conditions are important in determining intelligence.

One of the important environmental effects seems to be breast-feeding. Children who are breast-fed generally perform better in IQ tests than do those fed on other types of milk. Researchers think that this might be because specific fatty acids found in human milk, but not in cow’s milk or infant formulas, improve brain development.

Avshalom Caspi and Terrie Moffitt, psychologists at King’s College, London, and their colleagues looked at the relationship between breast-feeding and intelligence to explore the possibility that in this case nature and nurture might be intimately linked.

The group first looked for genes that metabolize fatty acids, which in turn are important for the growth of neurons. Differences in such genes, they hypothesized, might moderate the intellectual advantage associated with breast-feeding. They searched the literature and gene databases and found a good candidate: a gene called FADS2.

Class test

The team then looked at more than 1,000 children in New Zealand who were born in 1972 and IQ tested at ages 7, 9, 11, and 13; a record was kept of which children had been breast-fed. The study was repeated with about 2,200 children in Britain who were born in 1994–95 and IQ tested at age 5. DNA tests were used to look at a specific spot in their FADS2 genes, to see which version or ‘allele’ of the gene they carried.

In children who carried at least one copy of a ‘C’ allele for FASD2, those who were breast-fed generally had a higher IQ than those who were not: by an average of 6.4 IQ points in the New Zealand study, and by 7.0 IQ points in the British one. By contrast, children carrying two ‘G’ alleles had roughly the same IQ irrespective of their diet. About 10% of the population is thought to be ‘GG’.

“We had a very strong hypothesis, but it could easily have turned out wrong, so we were pleased when the data fit the hypothesis in New Zealand, and then really delighted when it was confirmed in Britain,” says Moffitt. The team reports their findings in the Proceedings of the National Academy of Sciences1.

Why and how this genetic difference came into being is unclear. “It is almost as though the G allele evolved as a protective genotype for children who might not get enough breast-milk,” says developmental psychologist Linda Gottfredson at the University of Delaware in Newark.

Mother care

The result will help to settle the debate over whether breast-feeding is linked to intelligence because of the nutritional quality of the milk, or because mothers who breast-feed are the sorts of mothers who encourage child learning. “I think this research will settle that debate, or at the very least bring it near a close,” says epidemiologist Jean Golding at the University of Bristol, UK.

“Many of us are starting to think that ‘nature via nurture’ might be a better catch phrase”

Avshalom Caspi

It might also serve as a guide for researchers aiming to find the genetic factors that affect other complex developmental factors, such as height. Such studies are usually approached by scanning thousands of people in search for different alleles associated with the trait of interest. “This research is suggesting that simply looking at huge samples may be missing the point,” says psychologist and geneticist Matt McGue of the University of Minnesota in Twin Cities. He notes that using specific context clues, as was done in this study, is a more efficient way to look for a gene.

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And the finding contributes to the growing feeling that scientists shouldn’t think of nature or nurture acting in isolation from each other. “Our team has reported gene–environment interactions involved in depression, violence and psychosis ... with these new data, many of us are starting to think that ‘nature via nurture’ might be a better catch phrase,” says Caspi. 

  • References

    1. Caspi, A. et al. Proc. Natl Acad. Sci. USA doi: 10.1073_pnas.0704292104 (2007).
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