The Longitudinal Examination of Body Mass Index and Internalizing Symptoms among Canadian Adolescents

Child and adolescent overweight and obesity issues are a rising concern. The mental health correlates of weight issues for youth are gaining recognition within the literature. However, the cross-sectional literature indicates that the relationship between weight and mental health problems is unclear. Further, few longitudinal studies have been completed to date. Thus, the overarching goal of the present dissertation was to examine longitudinally the relationship between body mass index (BMI) and internalizing symptoms among Canadian youth (ages 10-17, N = 6,987, 50.6% boys) using Statistics Canada’s National Longitudinal Survey of Children and Youth (NLSCY), cycles 4 to 8. In order to achieve the abovementioned goal, the dissertation is presented as two distinct studies. Given differences in the availability of measures based on age group, developmental trajectories were mapped from ages 10 to 15 and follow-up measures were analyzed for ages 16 and 17. The first study focused on the relationship between the developmental trajectories of BMI and internalizing symptoms. This objective was achieved through a parallel-process growth curve analysis, whereby the latent variables (i.e., intercept, slope, and quadratic) of the growth curves of BMI and internalizing symptoms were regressed on one another to examine the relationships over time. Results indicated that there were gender differences in trajectories and in the relationships among trajectories. More specifically, the shape of the BMI trajectory among girls (i.e., linear) and boys (i.e., quadratic) differed, possibly reflecting gender differences in pubertal timing. Regarding the parallel-process analysis, among boys, factors of the BMI trajectory predicted changes in the trajectory of internalizing symptoms. Among girls, there was a bidirectional relationship between BMI and internalizing symptoms. As heterogeneity in BMI development exists, there may be groups of youth that are most vulnerable to problems. As such, the second study used growth mixture modelling to identify different trajectory classes of BMI. Then, the trajectories of internalizing symptoms and physical activity were modelled and plotted to explore patterns across classes. Three classes were found for both boys and girls: ‘normative,’ ‘increasing,’ and ‘decreasing’ classes. Demographic attributes such as socioeconomic status, pubertal status, parent health, and community setting, were examined as predictors of class membership. Significant attributes differed between boys and girls. For both boys and girls, youth in the ‘increasing’ classes demonstrated higher levels of internalizing symptoms and lower levels of physical activity compared to other classes. Findings highlight that gender differences exist in the relationship between BMI and mental health. Implications for research and practice are discussed.