Researchers at King's College London discovered that breastfeeding can increase the IQ of children when combined with the right genes. Based on two studies of 3,000 breastfed babies in Britain and New Zealand, breastfeeding was found to raise intelligence by an average of nearly seven IQ points if the children had a particular version of a gene called FADS2.
The known association between breastfeeding and slightly higher IQ in children is shown to relate to this particular gene in the babies and the findings are published on-line in the Proceedings of the National Academy of Sciences in the US.
Lead author Avshalom Caspi and colleagues Ben Williams, Ian Craig and Terrie Moffitt at the Institute of Psychiatry (IoP), King's College London, collaborated with colleagues from the University of Otago, New Zealand, together with Duke University and Yale University in the US.
Terrie Moffitt, Professor of Social Behaviour & Development, a co-author on the paper at the MRC Social, Genetic and Developmental Psychiatry Centre at the IoP, says: ‘There has been some criticism of earlier studies about breastfeeding and IQ saying that they didn't properly control for socioeconomic status, or the mother's IQ or other factors, but our findings give a fresh perspective different from those arguments by showing a physiological mechanism that could account for the difference.'
‘Nature works via nurture'
The researchers found that the baby's intellectual development was influenced by both genes and environment or, more specifically, by the interaction of its genes with its environment.
Moffitt continues: ‘The argument about intelligence has been about nature versus nurture for at least a century. However we have shown that in fact nature works via nurture to create better health outcomes. In this case the environment is breastfeeding, the gene is the FADS2 gene, and the outcome is better cognitive function.'
The FADS2 gene is inherited from both the mother and father's side and comes in two versions: C and G. Ninety per cent of the children in the two study groups had a “C” version of FADS2, which yielded higher IQ if they were breast-fed. The other 10 per cent, with only the “G” version of the gene, showed no IQ advantage or disadvantage from breastfeeding.
The gene was singled out for the researchers' attention because it produces an enzyme that helps convert dietary fatty acids into the DHA (docosahexaenoic acid) and AA (arachidonic acid) polyunsaturated fatty acids that have been shown to accumulate in the human brain during the first months after birth.
The first findings about breastfeeding and IQ appeared over a decade ago, and in the past 10 years many formula makers have added DHA and AA fatty acids to their products. The children in these studies however were born in 1972-73 in New Zealand and 1994-95 in England, before fatty acid supplementation in formula began.
Though uncertain as to whether such supplementation has made a difference in humans, laboratory studies in which rodents and primates were fed supplemental fatty acids have shown increased brain DHA concentrations and enhanced abilities in tests of learning, memory and problem-solving.
‘Our findings support the idea that the nutritional content of breast milk accounts for the differences seen in human IQ,' Professor Moffitt remarks. ‘But it's not a simple all-or-none connection: it depends to some extent on the genetic makeup of each infant.'
Professor Moffitt notes that the researchers were not especially interested in IQ or breastfeeding per se, but that the study fitted into a body of work they have undertaken on gene-environment interactions and the brain.
She concludes: ‘What we are really interested in proving to the mental health community is that genes often influence behaviour through sensitivity to environments. When looking at genetic effects on depression, violence, schizophrenia, or intelligence, the key bit that's often left out here is the environmental effects.'
The research was supported by the National Institute of Mental Health (US), the Medical Research Council (UK), the Health Research Council (New Zealand) and the Royal Society-Wolfson Research Merit Award (UK).