Promoting physical activity can improve population health. This study aimed to examine associations of leisure-time moderate-to-vigorous physical activity and active school transport with mental health, that is, symptoms of depression and anxiety, among 15-to 16-year-old adolescents. We also assessed the relationships with less-studied outcomes, such as chronic stress and visits to school psychologist. A nationwide Finnish cohort of eighth and ninth graders from the School Health Promotion study (32 829 participants; mean age 15.4 years; 53% girls) was studied. We used logistic regression to estimate odds ratios (OR), with models adjusted for major sociodemographic, health behavior, and physical activity variables. Key findings suggest that leisure-time moderate-to-vigorous physical activity is associated with better mental health in a dose-response manner. Even the smallest dose, 30 weekly minutes, was linked to 17% lower odds of chronic stress symptoms compared to inactivity (OR 0.83, 95% CI 0.71-0.96). Compared to nonactive transportation, more than 30 min of daily active school transport yielded 19% (OR 1.19, 95% CI 1.07-1.31) and 33% (OR 1.33, 95% CI 1.12-1.58) higher odds of depression symptoms and school psychologist visits, respectively. However, no associations were found for low-to-moderate daily active school transport levels (<30 min). This large-scale study further highlights a positive association between leisure-time physical activity and mental health among youth. Future

IntroductionAir pollution has been suggested to be associated with depression. However, current evidence is conflicting, and no study has considered different sources of ambient particulate matter with an aerodynamic diameter below 2.5 µm (PM2.5). We evaluated the associations of long-term exposure to PM2.5 from road traffic and residential wood combustion with the prevalence of depression in the Helsinki region, Finland.MethodsWe conducted a cross-sectional analysis based on the Helsinki Capital Region Environmental Health Survey 2015–2016 (N=5895). Modelled long-term outdoor concentrations of PM2.5 were evaluated using high-resolution emission and dispersion modelling on an urban scale and linked to the home addresses of study participants. The outcome was self-reported doctor-diagnosed or treated depression. We applied logistic regression and calculated the OR for 1 μg/m3 increase in PM2.5, with 95% CI. Models were adjusted for potential confounders, including traffic noise and urban green space.ResultsOf the participants, 377 reported to have been diagnosed or treated for depression by a doctor. Long-term exposure to PM2.5 from road traffic (OR=1.23, 95% CI 0.86 to 1.73; n=5895) or residential wood combustion (OR=0.78, 95% CI 0.43 to 1.41; n=5895) was not associated with the prevalence of depression. The estimates for PM2.5 from road traffic were elevated, but statistically non-significant, for non-smokers (OR=1.38, 95% CI 0.94 to 2.01; n=4716).ConclusionsWe found no convincing evidence of an effect of long-term exposure to PM2.5 from road traffic or residential wood combustion on depression.

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