Can early childhood lifestyle factors explain the relationship between breastfeeding and risk for overweight and obesity?

Purpose: A growing body of research suggests that breastfed children are at lower risk for childhood overweight. This relationship could be explained by factors correlated with breastfeeding such as childhood nutrition, physical activity and screen time. Our objective was to determine whether the relationship between breastfeeding duration and childhood overweight remains after accounting for these important lifestyle factors. Methods: We analyzed data from the Early Childhood Longitudinal Study-Birth Cohort, a nationally representative sample of American children born in 2001 (n~5,450). Linear regression characterized associations between lifestyle factors and breastfeeding duration (exclusively or mixed) in months. Logistic regression models predicted the probability of overweight (BMI ≥85th percentile) and obesity (BMI ≥95th percentile) in kindergarteners that were never breastfed, breastfed 1-4 months, and breastfed >4 months, controlling for child characteristics (e.g., race/ethnicity, birth weight, SES), maternal characteristics and behaviors (e.g., age, smoking during pregnancy, pre-pregnancy BMI), preschool diet and lifestyle. Results: Longer breastfeeding duration was significantly associated with healthier diet, more physical activity, and less screen time in preschool. After multivariate adjustment for controls, those who were breastfed >4 months had a significantly lower prevalence of overweight (33%, p<0.01) and obesity (15%, p<0.05) than those never breastfed (38% and 20% respectively). Compared to never breastfed kindergartners, those breastfed 1-4 months had a lower but insignificant probability of overweight and obesity. Conclusion: Breastfed children in the United States have healthier childhood lifestyles, but these lifestyle differences do not appear to explain the protective relationship between breastfeeding >4 months and obesity in kindergarten.