Duration of breastfeeding and early childhood growth: sex- and race-specific trajectories in a nationally representative birth cohort

Despite established nutritional benefits of human milk, evidence regarding breastfeeding’s protective effect against childhood adiposity remains equivocal across subpopulations. This study investigates sex- and race-specific heterogeneity in the longitudinal association between duration of breastfeeding and early childhood BMI percentile trajectories. Data were drawn from the Early Childhood Longitudinal Study, Birth Cohort, a nationally representative US prospective cohort ( N 8500). The primary outcome was child BMI percentile from anthropometric measurements taken at 9, 24, 36, 48 and 60 months. Breastfeeding duration was categorised as never, less than 6 months and 6 months or longer. Stepwise hierarchical linear modelling, specifying non–linear individual growth curves, was utilised. Models were stratified by sex and adjusted for maternal, obstetric and sociodemographic confounders. A distinct sex-specific effect of breastfeeding was identified, whereby a duration of 6 months or longer significantly lowered BMI percentile trajectories in girls ( b = −3·70, 95 % CI: −5·86, −1·54) but yielded no significant association in boys. BMI percentiles by race/ethnicity also varied between sexes. Among boys, only Hispanic infants exhibited significantly higher percentiles than Non-Hispanic (NH) Whites ( b = 4·61, 95 % CI: 2·63, 6·60), whereas among girls, both Hispanic ( b = 3·26, 95 % CI: 1·24, 5·29) and NH Black infants ( b = −3·14, 95 % CI: −5·38, −0·90) showed significant differences relative to NH Whites. No significant interaction emerged between breastfeeding duration and race/ethnicity. These findings suggest that paediatric obesity prevention strategies may benefit from considering sex-specific mechanisms and addressing the structural factors associated with racial disparities.