Background: Internet addiction and depression are important mental health concerns among adolescents. Although prior research has examined their bidirectional relationship, the underlying mechanisms remain unclear. Drawing on conservation of resources theory, this study examined their bidirectional relationship and tested the mediating role of self-control, with attention to gender differences. Methods: A two-wave longitudinal survey (T1: November 2021; T2: May 2022) was conducted in China among 1908 adolescents (1026 females, 882 males; mean age = 13.546, SD = 1.463). At both waves, participants completed self-report measures of internet addiction, self-control, and depression (using the Internet Addiction Scale, Self-Control Scale, and CES-D). Results: The cross-lagged model revealed a bidirectional positive association between internet addiction and depression (β = 0.088, p < 0.001; β = 0.082, p < 0.001). Although effect sizes were modest, their cumulative effects may be clinically meaningful. The mediation analysis revealed bidirectional indirect effects through self-control. T1 internet addiction indirectly predicted T2 depression through self-control (indirect effect = 0.009, 95% CI 0.003, 0.014), and T1 depression indirectly predicted T2 internet addiction through self-control (indirect effect = 0.016, 95% CI 0.009, 0.025). These findings highlight self-control as a key linking mechanism. In addition, the negative effect of T1 internet addiction on T2 self-control was stronger in males than in females (β = −0.156, p < 0.001; β = −0.049, p = 0.014; Wald χ2 = 4.903, p = 0.027). Conclusions: Internet addiction and depression show a bidirectional predictive relationship, and reduced self-control serves as the underlying mechanism sustaining this cycle. Males show greater depletion of self-control resources following internet addiction than females.
Zhou et al. (Thu,) studied this question.