Smart kid? (Image: F1 Online/Rex Features)

Breastfeeding improves later academic performance in boys but appears to have no such effect in girls.

Wendy Oddy at the Telethon Institute for Child Health Research in Subiaco, Western Australia, and colleagues, examined whether having been breastfed affected the test scores of over 1000 10-year-olds.

Studies have suggested that children who were breastfed have higher IQs than those who were not, but few separated out boys and girls. Mothers who breastfeed are on average wealthier and more educated, so Oddy’s team accounted for these factors.

Boys who were mainly breastfed for at least six months scored 9 per cent higher in mathematics and writing tests, 7 per cent higher in spelling and 6 per cent higher in reading, compared with boys fed with formula milk or breastfed for shorter periods. There were no significant differences in results for girls.

“We know that breast milk contains the optimal nutrients for development of the brain and central nervous system,” says Oddy, but the gender differences were surprising.

Hormone link

Oddy points out that other studies have suggested boys are more vulnerable to stress and adversity during critical periods of brain development. She speculates this could be because girls seem to be protected by higher levels of oestrogen during childhood. She says the improved academic performance of boys could be explained by oestrogen in breast milk having similar neuro-protective effects.

Some studies have suggested that fatty acids uniquely present in breast milk explain research showing that it can help babies become more intelligent. Whether or not these fatty acids help in boosting IQ may be linked to the presence of certain gene variants involved in their processing.

A large randomised trial conducted by Michael Kramer at McGill University in Montreal, Canada, concluded that prolonged breastfeeding was linked to higher IQ and academic ratings by teachers in Belarussian children at age 6, but found no sex differences.

“These results add to the evidence that longer and exclusive breastfeeding is beneficial for cognitive development,” says Kramer.

The World Health Organization recommends exclusive breastfeeding for at least six months, and states that failing to do so impairs intellectual and social development.

Journal reference: Pediatrics, DOI: 10.1542/peds.2009-3489