Associations between Physical Activity and Depressive Symptoms through Obesity and School Bullying among Adolescents

Physical activity has been shown to be associated with improved physical and mental health conditions and can reduce the risk of depressive symptoms among adolescents. While the underlying mechanisms thought to mediate the relation between physical activity and depressive symptoms have not been well-established, the current study investigated the association of physical activity with depressive symptoms and whether this relationship would be explained by obesity and experiencing school bullying. This study is a cross-sectional analysis of the data drawn from the 2019 Youth Risk Behavior Survey including a nationally-representative sample of U.S. high school students (N = 13677, Female N = 6885 (49.4%)). Self-report measures of physical activity (i.e., Youths’ participation in vigorous physical activity, physical education, and sports teams, score range = 0-3), depressive symptoms (yes/no), school bullying experience (yes/no), and obesity (yes/no) were used to conduct a series of binary logistic regression models. Among the total sample of 9th-12th graders, 44.1% of students reported that they were physically active for a total of at least 60 minutes per day on 5 or more days per week, and half of the participants were involved in physical education programs (52.2%) and 1 or more sports teams (57.4%). Regarding depressive symptoms, 36.7% of students reported feeling sad or hopeless almost every day for two weeks or more in a row during the path 12 months. After controlling the student’s sociodemographic factors (i.e., age, sex, race/ethnicity, grade), higher levels of physical activity significantly decreased the odds of depressive symptoms by 16.4% (OR = 0.836; 95% CI = 0.805, 0.868; p < 0.001) as well as being obese by 20.2% (OR = 0.798; 95% CI = 0.757, 0.841; p < 0.001) and being bullied at school by 5.3% (OR = 0.947; 95% CI = 0.905, 0.991; p = 0.019). In a subsequent analysis including obesity and school bullying as simultaneous regressors with physical activity, the magnitude of the association between physical activity and depressive symptoms was attenuated (OR = 0.825; 95% CI = 0.791, 0.860; p < 0.001), and obesity (OR = 1.276; 95% CI = 1.137, 1.431; p < 0.001) and school bullying (OR = 3.572, 95% CI = 3.231, 3.948; p < 0.001) were significantly associated with increased odds of depressive symptoms. These findings suggest that physical activity is inversely related to depressive symptoms and may help to mitigate the negative effects of mood disorders among adolescents via biological and psychosocial processes (i.e., obesity, school bullying). Elucidating the processes underpinning the effects of physical activity on depressive symptoms among adolescents may provide the necessary impetus for schools and policy makers to prioritize the promotion of physical activity.