Almost 3500 participants in Brazil were followed up from birth in 1982 until they were around 30 years old to try and assess whether there were long-term differences between those who had been breastfed and those who had not. The variables that were studied were intelligence—as assessed by a widely used intelligence test (Wechsler Adult Intelligence Scale, 3rd version)—educational attainment, and income.

The study contributed important knowledge about three issues related to the effects of breastfeeding on cognitive development. Firstly, the study’s findings showed the effects of breastfeeding in a cultural and economic setting without strong social patterning of breastfeeding; second, it investigated long-term effects of breastfeeding during a substantial part of the full lifespan; and third, it described life course consequences of breastfeeding by incorporating socially important outcomes, such as education and income.

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