Nothing could be further from the truth.
Some studies show an increase in intelligence for each additional month the child was breastfed.
Below are two articles summarizing the findings of the Christchurch School of Medicine in New Zealand, which followed 1,000 children for 18 years to establish the relationship between intelligence and breastfeeding. Below that are references on 7 other separate studies that show a correlation between breastfeeding and cognitive development. Breast-Fed Make Better Grades . Breastfeeding during infancy of the American Academy of Pediatrics. R esearchers from Christchurch School of Medicine in New Zealand studied over 1,000 children born between April and August 1977.