Depression is one of the most prevalent mood disorders during adolescence and has profound implications for mental health and overall well-being. However, the mechanisms through which depression influences adolescent mental health remain insufficiently understood, particularly regarding modifiable psychosocial factors. Quality of life (QL) and sleep regularity (SR) have been identified as important correlates of both depression (DPS) and mental health (MH), yet their sequential roles have rarely been examined within a single explanatory framework. A cross-sectional survey was conducted among 487 late adolescents using validated self-report instruments measuring depression, quality of life, sleep regularity, and mental health. Data were analyzed using partial least squares structural equation modeling (PLS-SEM) to assess the measurement model, structural relationships, and mediating effects. Bootstrapping with 5,000 resamples was employed to test indirect and sequential mediation effects. Depression was found to be negatively associated with quality of life (β = −0.344, p < 0.001). Quality of life positively predicted sleep regularity (β = 0.276, p < 0.001), which in turn was positively associated with mental health (β = 0.232, p < 0.01). Mediation analyses revealed that quality of life partially mediated the relationship between depression and mental health (β = −0.144, p < 0.001) and between depression and sleep regularity (β = −0.095, p < 0.001). Furthermore, a significant sequential mediation effect was observed, indicating that depression indirectly influenced mental health through the combined pathways of quality of life and sleep regularity (β = −0.022, p = 0.001). The model demonstrated acceptable explanatory power and overall fit. The findings indicate that depressive symptoms are statistically associated with lower positive mental health among late adolescents, both directly and indirectly through quality of life and sleep regularity. These results suggest that quality of life and sleep regularity represent potentially modifiable psychosocial and behavioral correlates within this association. However, given the cross-sectional design, the observed pathways should be interpreted as patterns of association rather than evidence of temporal or causal effects. Future longitudinal and intervention-based studies are needed to clarify the directionality and practical implications of these relationships. Not applicable.
Yan et al. (Mon,) studied this question.