Effects of Reallocating Physical Activity, Sedentary Behaviors, and Sleep on Mental Health: A Cross-Sectional Examination of Canadian Adolescents in the COMPASS Study

Abstract

Background: Physical activity, sedentary behavior, and sleep are associated with mental health in adolescents. Mental health may depend not only on the amount of time spent in a specific activity, but also on the activity it displaces. The aim of this study was to examine the impact of reallocating 15 minutes of time spent in one health behavior with 15 minutes in another on adolescent mental health. Methods: Cross-sectional data from the students participating in the COMPASS Study (2018-2019) were analyzed (N = 46,413). Participants self-reported the amount of time they spent engaged in moderate-to-vigorous physical activity (MVPA), doing homework and using screens, and their sleep duration on average each day. Participants also self-reported depressive symptoms, anxiety, and flourishing. Data were analyzed using isotemporal substitution modeling. Results: Non-linear associations were evident between sleep and the mental health outcomes, so analyses were stratified by sleep duration based on whether students reported meeting current guidelines or not. Among adolescents getting less than the recommended amount of sleep, replacing any behaviour with sleep was generally associated with better mental health outcomes. Conversely, among adolescents getting adequate sleep, the findings did not support replacing other behaviors with sleep with the exception of screen time. Replacing homework and MVPA with sleep was associated with less flourishing regardless of sleep duration. Of the two sedentary behaviors assessed, replacing screen time with homework was associated with less depression and greater flourishing. However, replacing any behavior with homework was associated with greater anxiety regardless of whether participants reported adequate sleep or not.Conclusions: Replacing screen time with any behaviour may be better for mental health outcomes. Results provide further support for the critical role of sleep in promoting healthy development during adolescence, though more sleep than is recommended may confer little benefit for mental health. Youth getting adequate sleep may benefit from replacing screen time with homework or MVPA. The findings demonstrate that mental health benefits may be obtainable at intervals as short as 15 minutes.