School level contextual factors are associated with the weight status of adolescent males and females.

OBJECTIVE: To determine whether school context influences the BMI of adolescent males and females. METHODS AND PROCEDURES: Our sample was 17,007 adolescents (aged 12-19) from the National Longitudinal Study of Adolescent Health (Add Health). We used gender-stratified multilevel modeling to examine the contribution of schools to the overall variance in adolescent BMIs, calculated from self-reported weight and height. We then examined the associations of individual attributes with BMI after controlling for the average BMI of the school and the association of two school-level variables with BMI.
RESULTS: Participants attended schools that were segregated by race/ethnicity and socioeconomic status (SES). In females, when controlling only for individual-level attributes, individual household income was inversely associated (beta = -0.043, P = 0.01) while Hispanic (beta = 0.89, P < 0.001) and black (beta = 1.61, P < 0.001) race/ethnicity were positively associated with BMI. In males, Hispanic (beta = 0.67, P < 0.001) race/ethnicity was positively associated with BMI; there was no difference in the BMIs of blacks compared with whites (beta = 0.24, P = 0.085). After controlling for the school racial/ethnic makeup and the school level median household income, the relationship between individual race/ethnicity and BMI was attenuated in both male and female adolescents. Higher school level median household income was associated with lower individual BMIs in adolescent girls (gamma = -0.37, P < 0.001) and boys (gamma = -0.29, P < 0.001) suggesting a contextual effect of the school. DISCUSSION: Male and female adolescents attending schools with higher median household incomes have on average lower BMIs. Resources available to or cultural norms within schools may constitute critical mechanisms through which schools impact the BMI of their students.