Breastfeeding and Development of Attention-Deficit/Hyperactivity Disorder Symptoms Across Childhood

Background Studies suggest that breastfeeding may be associated with a reduced risk of childhood ADHD. However, determining causality is challenging because potential confounders, including genetic predisposition, may influence this relationship. We prospectively examined the relationship between full (exclusive or predominant) breastfeeding duration and ADHD symptoms in children, accounting for sociodemographic and perinatal factors and polygenic risk of ADHD. Methods We obtained data from 37,643 children (49.1% girls) born 1999-2009, and 18,349 mother-father-child units from the Norwegian Mother, Father and Child Cohort Study. We examined the effect of full breastfeeding per month (self-reported when the child was 6 months old) on parent-rated ADHD symptoms in offspring at 3, 5 and 8 years (multivariate regression models). Measures are expressed as unstandardized regression coefficients (B) with 95% confidence intervals, adjusting for socioeconomic and perinatal factors, and ADHD polygenic scores in child, mother, and father. Results Full breastfeeding per month was significantly associated with lower ADHD symptoms at all ages (adjusted B age3 = -0.08(-0.09, -0.07); B age5 = -0.07(-0.08, -0.06); B age8 = -0.06(-0.07, -0.05)), indicating that each month of full breastfeeding associated with lower ADHD symptoms. Similar results were observed when modelling breastfeeding as a categorical variable including both full and partial breastfeeding. Inverse probability weighting, accounting for loss to follow-up, and sibling analyses with discordant breastfeeding exposures, accounting for unmeasured confounding, supported the main results. Conclusions Our findings suggest that full breastfeeding could partially protect against childhood ADHD symptoms. Further studies are needed to understand the potential mechanisms of the association between breastfeeding and lower ADHD symptoms.