Exploring gender differences in the longitudinal association between bullying and risk behaviours with Body Mass Index among COMPASS youth in Canada.

The purpose of this study was to identify gender differences in the association between bullying and Body Mass Index (BMI) longitudinally. Longitudinal data (2013-2015) from 4510 youth (Ontario, Canada) were used to model BMI with consecutive bullying status prospectively, adjusting for previously identified gender-specific health risk behaviour latent classes. To assess for gender differences, these mixed-effects models were stratified by gender. Youth who were victims of bullying (VoB) were more active, engaged in more substance use and reported higher BMI than their non-victim of bullying (NVoB) peers. The gender-specific mixed-models showed that there are gender differences in the association between bullying and BMI. Among females, repeated bullying was associated with higher odds of having overweight/obesity [by 51% (95% C.I. = 1.03, 2.23)] at follow-up. Among male youth, being a VoB at the previous wave only, was associated with higher odds of having overweight/obesity [by 60% (95% C.I. = 1.11, 2.29)] at follow-up. In contrast with previous literature that measured BMI during adulthood (i.e., years after school victimization), our study adds a unique contribution to the literature that across one year (while youth are still in secondary school), bullying is associated with higher odds of weight status and BMI among female and male youth. Since this increase occurs during secondary school, school-based programs aimed at decreasing youth bullying behaviours and addressing increases in BMI before youth leave school are of paramount importance.