Children who are breastfed for longer go on to become more intelligent, educated and successful adults, according to a recent study.
Scientists in Brazil analysed breastfeeding data on almost 3,500 babies who were given IQ tests when they reached the age of 30, providing information on educational attainment and income.
Dr Bernardo Lessa Horta, from the Federal University of Pelotas, said the study provides the "first evidence" that prolonged breastfeeding "not only increases intelligence until at least the age of 30 years but also has an impact both at an individual and societal level".
Participants were divided into five groups based on the length of time they were breastfed as infants.
The researchers took account of factors that might influence IQ, such as genetics, birth weight, parental schooling and whether or not the mother smoked during pregnancy.
According to the results of the study, breastfeeding was generally found to increase:
Length of schooling
Someone who had been breastfed for at least a year reportedly gained four more IQ points, on average, at the age of 30 than a person who had been breastfed for less than a month.
The research has been published in The Lancet Global Health journal.