The association of physical activity, sleep, and screen time with mental health in Canadian adolescents during the COVID-19 pandemic: A longitudinal isotemporal substitution analysis

BACKGROUND: The impact of COVID-19 on adolescent mental health is a global concern. Increased screen time and reduced physical activity due to the lockdown measures have been linked to detrimental mental health outcomes; however, the literature remains limited by cross-sectional and retrospective designs, and consideration of behaviours in isolation. Prospective evidence is necessary to examine whether moderate-to-vigorous physical activity (MVPA), sleep and screen time influenced changes in mental health. METHOD: Analyses used data from a prospective cohort study of secondary school students in Canada with baseline data from the 2018–2019 school year and linked follow-up data from online surveys completed during the initial COVID-19 outbreak (May–July 2020). Multilevel linear regression models were used to evaluate the within- and between-person isotemporal substitution effects of sleep, MVPA and screen time behaviours on depression, anxiety, subjective well-being, and trait emotional dysregulation. RESULTS: Linked longitudinal data from 2645 students attending 44 schools were available. Between-person effects indicated that individuals who engaged in more MVPA and sleep while minimizing screen time had lower depression scores, less severe emotional dysregulation, and better subjective well-being. While controlling for between-person effects, within-person year-on-year change suggests those who increased screen time while decreasing either MVPA or sleep experienced mental health decline on all outcomes. CONCLUSION: MVPA and sleep were associated with youth mental health during the early COVID-19 lockdown. Increasing MVPA and sleep (or at least mitigating the increase of screen time) compared to the prior year was associated with better mental health during the early pandemic. A limitation to consider is that the screen time measure represents a combination of screen behaviours, and effects of replacing screen time may have varied if distinctions were made.