{"p"=>{"__content__"=>"To examine the associations between sleep,outdoor activity, sedentary time, and depressive symptoms among secondaryschool students in Wuhan, using an isotemporal substitution model. This prospective cohort study included 2,615 secondary school students in Wuhan. All participants were free of depressive symptoms at baseline in September 2023 and were followed up in September 2024. Sleep duration, outdoor activity time, and sedentary time were assessed using questionnaire surveys, and depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CES-D). Multivariate logistic regression models were applied to analyze the association between time-use behaviors and depression. Restricted cubic spline models were used to explore the dose-response relationship. Isotemporal substitution models were further employed to evaluate the impact of time reallocation between different behaviors on depression risk under the assumption of fixed total time. A total of 2,615 secondary school students were included in this study. After one year of follow-up, 456 students developed depression (17.4%). Sleep duration was inversely associated with incident depressive symptoms, while sedentary time was positively associated with depressive symptoms ( < 0.05). However, after adjustment for relevant confounders, the association between sedentary time and depressive symptoms was no longer statistically significant. Isotemporal substitution analysis revealed that, with total time spent in the assessed behaviors held constant, replacing 1 h of sedentary time (OR = 0.89, 95% CI: 0.81–0.97,  = 0.008) or 1 h of outdoor activity time (OR = 0.84, 95% CI: 0.73–0.97,  = 0.019) with 1 h of sleep was associated with a lower risk of incident depressive symptoms. Sufficient sleep was consistently associated with a lower risk of depressive symptoms among secondary school students, whereas sedentary time may be a potential risk factor that requires further investigation in future studies.", "i"=>[{"__content__"=>"P"}, {"__content__"=>"P"}, {"__content__"=>"P"}]}}