KEY POINTS:
Breastfeeding can have a positive effect on the IQ of children when combined with the right genes, says an Otago University study.
The findings, published this week in the journal Proceedings of the National Academy of Science, come out of the university's Dunedin multidisciplinary health and development study.
Study director Professor Richie Poulton said previous studies had shown that breastfed children averaged higher IQ scores than non-breastfed children.
"However, not all breastfed children show this higher IQ score.
"What we and our international collaborators have found is that they also have to have a certain version of a gene called FADS2," Dr Poulton said.
"We were able to rule out other potential explanations for the IQ findings, including the mother's socioeconomic status and birth weight of the baby."
Researchers followed two groups of people - 1000 Dunedin-born study members and 2200 British children born in 1994-95.
The IQ of all study members was tested, and the mothers of study members were asked about breastfeeding practices.
The FADS2 gene is inherited from both the mother's and father's side.
The gene comes in two versions: C and G. Children inherit either two of the C version, one each of C and G, or two of the G version.
The C version of the FADS2 gene is associated with more efficient processing of the omega-3 and omega-6 fatty acids found in breast milk. This may in turn help brain development and function, though the exact link is not yet known.
The researchers found that children with the C version of the gene averaged slightly higher IQ scores when breastfed as babies than those who were not breastfed. This IQ advantage was about 6 to 7 points.
Breastfeeding had no effect on children with two of the G version of the gene. IQ scores were neither advantaged nor disadvantaged.
"Their IQ was still in the normal healthy range," Prof Poulton said.
In total, 90 per cent of the children studied had either one or two of the C version of the gene, and 10 per cent had two G versions of the gene.
Prof Poulton said both genetic makeup and environmental factors were important.
"This shows that the argument is not nature versus nurture any more. We're finding that nature and nurture actually work together to produce health outcomes.
"This is true across all sorts of health areas, including positive outcomes like this study, and work involving mental health disorders."
The research was supported by the Health Research Council (NZ), the National Institute of Mental Health (US), and the Medical Research Council (UK).
- NZPA