Aim: To assess the effect of breastfeeding duration on school achievement in a Brazilian cohort.
Methods: In a population-based birth cohort, we analysed the highest grade achieved in school of over 2,000 male 18-y-olds relative to breastfeeding information collected in early life. Analyses were adjusted for birthweight, family income, maternal and paternal schooling, household assets, number of siblings, social class, maternal smoking during pregnancy, and ethnicity.
Results: After adjustment for confounding variables, there was a highly significant trend in school achievement with increasing breastfeeding duration. Those breastfed for 9 mo or more were ahead by 0.5-0.8 school grades, relative to those breastfed for less than 1 mo. Data from a cross-sectional survey in the same population suggest that such a difference corresponds to a 10-15% difference in adult income levels. The duration of exclusive or predominant breastfeeding was also positively associated with schooling.
Conclusion: Unlike studies from developed countries, there was no clear association between breastfeeding duration and either the family's socio-economic level or parental schooling in our sample and therefore residual confounding is improbable. These results suggest that the impact of breastfeeding on intellectual development may lead to sizeable differences in adult education and wage-earning performance.