Association between depression and sleep disorder and the mediating role of smartphone addiction: a longitudinal study of Chinese college freshmen during the COVID-19 pandemic

Previous studies have identified a bidirectional association between depression and sleep disorders (SD). However, it remains unclear whether this association has changed in the new social context of the COVID-19 pandemic. Therefore, we aim to investigate the bidirectional association between depression and SD among college freshmen and the mediating role of smartphone addiction (SA) during the COVID-19 pandemic. Two waves of cross-sectional surveys were conducted among 1186 college freshmen, collecting data on depression, SD, SA and physical activity. Cross-lagged mediation models were employed to examine the bidirectional association between depression and SD, as well as the mediating role of SA. Additionally, two stratified analyses were conducted to explore the potential modifying effects of gender and physical activity. Cross-lagged analysis demonstrated that the bidirectional association between depression and SD had changed, with baseline depression significantly predicting subsequent SD, but not vice versa. Mediating analysis revealed that SA partially mediated the pathway from depression to SD, and fully mediated the pathway from SD to depression. Furthermore, stratified analyses indicated that the association between depression and SD varied by gender and the amount of time spent on daily physical activity. Our results did not support a bidirectional association between depression and SD during the COVID-19 pandemic. SA may be an important pathway in the bidirectional association between depression and SD. Reducing SA and increasing physical activity may help break the vicious cycle between depression and SD, improving negative mood, SD, and SA.