A moderated mediation model explains the association between sedentary time and depressive symptoms among Chinese university students

Background Sedentary behavior is a critical public health concern for university students and linked to increased depressive symptoms, yet its mechanisms are unclear. This study aimed to examine the relationship between sedentary time and depressive symptoms among Chinese university students, with a focus on sleep quality as a mediator and sports participation as a moderator. Methods A cross-sectional survey was conducted among 2,661 college students from one university in Jiangsu, China. Data were collected using a validated self-report questionnaire including sedentary time, depressive symptoms, sleep quality, and sports participation. Model 4 and Model 59 in Hayes' PROCESS macro for SPSS were employed to test both the mediation effect and the moderated mediation model. Results Sleep quality partially mediated the relationship between sedentary time and depressive symptoms, accounting for 68.6% of the total effect ( effect = 0.074, 95% CI [0.049, 0.113]). Sports participation moderated the indirect effect: the link between sedentary time and sleep quality ( β = -0.044, p < 0.01), and between sleep quality and depressive symptoms ( β =-0.093, p < 0.001) weakened with higher sports participation. However, sports participation did not moderate the direct effect of sedentary time on depressive symptoms. Conclusions Sedentary time contributes to depressive symptoms indirectly through poor sleep quality. Sports participation buffers these effects by improving sleep quality and reducing the psychological impact of sedentary behavior. Interventions targeting sleep hygiene and promoting sports participation may mitigate depression risk in university students.