A moderated mediation model of depression and insomnia in adolescents

This study aimed to examine the association between depression and insomnia among adolescents and to investigate the mediating role of short video addiction (SVA) and the moderating role of physical activity (PA) in this association. A cross-sectional questionnaire survey was conducted among 725 adolescents from Hunan and Sichuan provinces, China. Depression, insomnia, SVA, and PA were assessed using standardized measures. Descriptive statistics and correlation analyses were performed using SPSS 26.0. The PROCESS macro for SPSS was used to test the mediating effect of SVA (Model 4) and the moderated mediation model involving PA (Model 7), with 5,000 bootstrap resamples used to estimate 95% confidence intervals. Depression was positively associated with both SVA and insomnia, whereas PA was negatively associated with depression and SVA. SVA partially mediated the association between depression and insomnia, with the indirect effect accounting for 6.94% of the total effect. PA significantly moderated the association between depression and SVA ( β = −0.095, SE = 0.044, t = − 2.169). Simple slope analysis further showed that the positive association between depression and SVA progressively weakened as PA levels increased, with conditional effects of β = 0.313 at one standard deviation below the mean, β = 0.269 at the mean, and β = 0.173 at one standard deviation above the mean. SVA may represent one behavioral pathway linking depressive symptoms with insomnia among adolescents, although its mediating effect was relatively modest. Higher levels of PA were associated with a weaker positive relationship between depression and SVA, suggesting a potential protective role of PA. From a practical perspective, these findings support the potential value of school-based mental health strategies that increase opportunities for regular PA through physical education, active recess, and extracurricular sports, while also providing guidance on reducing excessive short-video use, particularly before bedtime, and promoting healthy sleep habits. Given the cross-sectional design, these implications should be interpreted cautiously and further evaluated in longitudinal and intervention studies.