Longer Breastfeeding Is Associated With Healthier Body Mass Index Trajectories and Lower Risk of Overweight and Obesity in Youth Aged 9-12 Years.

BACKGROUND

The association between breastfeeding and adolescent obesity remains unclear because most previous studies included youth with obesity. We explored these associations from ages 9 to 12 amongst initially healthy weight youth.

METHODS

The analytic sample included 4161 youth (10 586 observations across three assessments; all healthy weight at baseline; 50.7% female; 52% breastfed more than 6 months) from the Adolescent Brain Cognitive Development (ABCD) Study. Linear mixed-effects models examined breastfeeding × age × sex and breastfeeding × puberty × sex interactions on BMI trajectories (kg/m2). Logistic regression estimated the risk of unhealthy weight (BMI ≥ 85th percentile) by ages 11-12. All analyses were stratified by sex.

RESULTS

Three-way interactions were not significant. Significant breastfeeding × age interactions (β = -0.005, p < 0.001) indicated that breastfed youth exhibited lower BMI trajectories, particularly when breastfed for more than 6 months (β = -0.006, p < 0.001). Significant breastfeeding × puberty interactions showed lower BMI trajectories across pubertal stages amongst breastfed youth (β = -0.06, p = 0.017), observed only in boys and especially in those breastfed beyond 6 months (β = -0.11, p = 0.005). Breastfeeding was associated with a reduced unhealthy weight risk at ages 11-12 (RR = 0.78, p = 0.002), exclusively in boys and amongst those breastfed more than 6 months (RR = 0.52, p < 0.001). No associations were found in girls.

CONCLUSION

Amongst initially healthy weight youth, breastfeeding, especially beyond 6 months, was associated with healthier BMI trajectories and lower unhealthy weight risk in boys. Although these sex-specific patterns warrant further research, our findings suggest that the associations between breastfeeding and body weight development extend into adolescence.