"Our study provides the strongest evidence to date that prolonged and exclusive breastfeeding makes kids smarter," said Kramer, a Professor of Pediatrics and of Epidemiology & Biostatistics in the McGill University Faculty of Medicine and lead investigator in the study.

Kramer and his colleagues evaluated the children in 31 Belarusian hospitals and clinics. Half the mothers were exposed to an intervention that encouraged prolonged and exclusive breastfeeding. The remaining half continued their usual maternity hospital and outpatient pediatric care and follow-up. This allowed the researchers to measure the effect of breastfeeding on the children’s cognitive development without the results being biased by differences in factors such as the mother’s intelligence or her way of interacting with her baby.

The children’s cognitive ability was assessed by IQ tests administered by the children’s pediatricians and by their teachers’ ratings of their academic performance in reading, writing, mathematics and other subjects. Both sets of measures were significantly higher in the group randomized to the breastfeeding promotion intervention.

"The effect of breastfeeding on brain development and intelligence has long been a popular and hotly debated topic,” says Dr. Kramer. "While most studies have been based on association, however, we can now make a causal inference between breastfeeding and intelligence – because of the randomized design of our study.”