Abstract
OBJECTIVE: This study aimed to examine the associations between internet addiction (IA), physical activity (PA), and mental health comorbidities (depression, anxiety, and their co-occurrence) among Chinese adolescents, and assess the mediating role of PA in the IA-mental health relationship. METHODS: A cross-sectional analysis was conducted using data from the 2024 National Student Common Diseases and Risk Factors Surveillance (NSCDRFS) in Tianjin, China, involving 20,692 adolescents aged 12-19 years. IA was assessed via a DSM-5-derived 9-item scale (cutoff ≥ 5). PA levels were categorized as insufficient (≤ 2 days/week of moderate-to-vigorous activity). Mental health outcomes included depressive symptoms (CES-D ≥ 16), anxiety symptoms (GAD-7 ≥ 10), and anxiety-depression comorbidity (ADC), defined as meeting both depression (CES-D ≥ 16) and anxiety (GAD-7 ≥ 10) diagnostic criteria. Multivariable logistic regression and mediation analyses were performed to evaluate direct and indirect pathways. RESULTS: Adolescents with IA exhibited significantly higher risks of anxiety (OR = 1.80, 95% CI: 1.68-1.91), depression (OR = 1.99, 95% CI: 1.88-2.11), and ADC (OR = 2.12, 95% CI: 2.00-2.25) compared to non-IA peers (all P < 0.001). Insufficient PA independently increased risks of anxiety (OR = 1.17), depression (OR = 1.27), and ADC (OR = 1.23). Mediation analysis revealed that PA accounted for only 3.5-4.3% of the total effects of IA on mental health outcomes, with direct effects remaining predominant (95.7-96.5%). Subgroup analyses highlighted stronger IA-mental health associations in younger adolescents (12-15 years), non-boarding students, and junior high school cohorts. CONCLUSION: IA is an independent risk factor for mental health comorbidities in Chinese adolescents, with PA serving as a minor yet significant mediator. Targeted interventions should integrate IA screening, culturally adapted PA promotion, and digital literacy education to address this triad. Future longitudinal studies are needed to elucidate causal pathways and neurodevelopmental mechanisms.