Social connections with family and friends in adolescence: Shaping body mass index trajectories into adulthood.

To investigate whether adolescent social connections influence body mass index (BMI) trajectories into adulthood and explore whether associations are moderated by gender, ethnicity or age. Data came from 17,719 American adolescents in grades 7-12 at baseline (1994-95) from the National Longitudinal Study of Adolescent to Adult Health. Growth curve models tested associations between baseline social connections and BMI trajectories from waves II-V including interactions for gender, ethnicity and age. Stronger peer connections were associated with flatter BMI trajectories. For example, BMI for those with high peer contact was 0.79 kg/m2 lower [95% CI -1.20, -0.38] 22 years after baseline, compared to those with low contact. Stronger family connections were associated with steeper trajectories. For example, BMI for those with high family contact was 0.52 kg/m2 higher [95% CI 0.01, 1.02] 22 years after baseline, compared to those with low contact. Among adolescents, stronger peer connections were associated with flatter BMI trajectories and stronger family connections with steeper trajectories. Promotion of peer-based interventions could be explored as a strategy to promote healthy weight trajectories.