Is breast feeding associated with offspring IQ at age 5? Findings from prospective cohort: Lifestyle During Pregnancy Study

Objectives Breast feeding is associated with health benefits for both mother and child, but many studies focusing on neurodevelopment have lacked information on important confounders and few randomised trials exist. Our objective was to examine the influence of breast feeding on child IQ at 5 years of age while taking maternal IQ and other relevant factors into account. Design Prospective observational study. Setting Population-based birth cohort in Denmark. Participants We used data from The Lifestyle During Pregnancy Study 1782 mother-child pairs sampled from the Danish National Birth Cohort (n=101 042). Outcome measures Child IQ was assessed at age 5 years by the Wechsler Primary and Preschool Scales of Intelligence-Revised. On the same occasion maternal intelligence was assessed by Wechsler Adult Intelligence Scale and Raven's Standard Progressive Matrices. Exposure data on duration of breast feeding (n=1385) were extracted from telephone interviews conducted when the child was 6 and 18 months, and analyses were weighted by relevant sampling fractions. Results In multivariable linear regression analyses adjusted for potential confounders breast feeding was associated with child IQ at 5 years (categorical chi(2) test for overall association p=0.03). Compared with children who were breast fed <= 1 month, children breast fed for 2-3, 4-6, 7-9 and 10 or more months had 3.06 (95% CI 0.39 to 5.72), 2.03 (95% CI -0.38 to 4.44), 3.53 (95% CI 1.18 to 5.87) and 3.28 (95% CI 0.88 to 5.67) points higher IQ after adjustment for core confounders, respectively. There was no dose-response relation and further analyses indicated that the main difference in IQ was between breast feeding <= 1 month versus >1 month. Conclusions Breastfeeding duration of 1 month or shorter compared with longer periods was associated with approximately three points lower IQ, but there was no evidence of a dose-response relation in this prospective birth cohort, where we were able to adjust for some of the most critical confounders, including maternal intelligence.