Long - term study found that mortality at age 30 was nearly 4 times higher for babies staying for a month or more . Study conducted in Brazil also associates longer periods with higher income and fertility levels . Critic points out that the study does n't account for other possible contributing factors .
Long-term study finds that IQ at age 30 was nearly 4 points higher for babies breastfed for a year or more . Study conducted in Brazil also associates longer breastfeeding with higher income and education levels . Critic points out that the study does n't account for other possible contributing factors .