The longer a baby is breastfed, the more likely it is to grow up to be intelligent, stay in school and earn a better salary, according to new research.
Previous studies have demonstrated the short term benefits of breastfeeding, but previous evidence of its long-term effects has been criticised for failing to take into account the fact that in many countries socially advantaged children are more likely to be breastfed in the first place.
The new research, published in The Lancet medical journal, was carried out in a Brazilian population where, it is claimed, there was no difference in breastfeeding rates between different social classes.
Facebook updates banned content guidelines, including nudity
Mothers prevented from breastfeeding at breastfeeding conference
Nearly 3,500 babies born in Pelotas, Brazil, in 1982, were followed up 30 years later and given an IQ test and asked about their education and income.
Those who had been breastfed for a year had on average four more IQ points, had spent nearly a year longer in school and had a higher income of around 341 Brazilian reais (£70) per month.
Dr Bernado Lessa Horta, of the Federal University of Pelotas, who led the study, said that a group of fatty acids called docosahexaenoic acids (DHAs) found in breast milk were essential for brain development, possibly explaining the impact on intelligence.