Infants whose mothers drank alcohol while breast-feeding had lower cognition scores by age 6, according to an observational study.

Australian researchers followed over 5,000 children from infancy through age 11. Roughly 4,700 of these infants were ever breast-fed. Mothers were asked about their alcohol intake during breastfeeding.

After controlling for potential confounders, heavier maternal alcohol consumption during breast-feeding was associated with lower nonverbal reasoning scores in a dose-response manner at age 6–7 years. By age 10–11, the difference was no longer significant. The authors suggest that variables like increased education by this age may mediate the effects of alcohol exposure.

Commentators note: "Although findings in this study were independent of prenatal alcohol consumption, pregnancy alcohol use was recorded by maternal self-report retrospectively, and there are often multiple psychosocial and other pressures for women to deny gestational substance use."