Digital addiction comorbidity patterns and their differential links to internalizing symptoms, suicidal behaviors and non-suicidal self-injury in vocational high school students

Abstract

Digital addiction is a growing public health concern among adolescents, yet evidence on co-occurring addiction patterns and their differential associations with mental health outcomes remains limited, particularly in vocational students. A cross-sectional survey of 15,311 vocational high school students was conducted in Zigong, China. Smartphone, gaming, and social media addiction were assessed using validated scales. Participants were classified into no addiction, single addiction, and multiple addictions groups. Outcomes included internalizing symptoms (clinically significant depression or anxiety), suicidal behaviors (ideation, planning, or attempts), and non-suicidal self-injury (NSSI). Hierarchical regression models with progressive adjustment were supplemented by sensitivity analyses using continuous scores and operating characteristic (ROC)-derived alternative cut-offs. A total of 20.9% of participants met the criteria for one form of digital addiction, with smartphone-only addiction being the most prevalent pattern (19.4%). A graded association was observed, with the prevalence of all adverse outcomes increasing progressively with the number of addictions (all p < 0.001). In fully adjusted models, single addiction was associated with internalizing symptoms (OR = 1.77, 95% CI: 1.54-2.04), suicidal behaviors (OR = 1.38, 95% CI: 1.24-1.52), and NSSI (OR = 1.42, 95% CI: 1.24-1.63). Multiple addictions were associated with internalizing symptoms (OR = 5.58, 95% CI: 3.71-8.41) and suicidal behaviors (OR = 2.56, 95% CI: 1.74-3.77), but the association with NSSI was attenuated (OR = 1.17, 95% CI: 0.81-1.70, p = 0.404). When the three continuous addiction scores were mutually adjusted, smartphone addiction severity remained independently associated only with internalizing symptoms (OR = 1.05, 95% CI: 1.04-1.06), whereas gaming and social media addiction severities were independently associated with both suicidal behaviors and NSSI. Triple addiction was associated with the highest risk of suicidal behaviors (OR = 3.42, 95% CI: 1.62-7.21). Sensitivity analyses using data-driven ROC-optimal cut-offs preserved the core graded pattern. Co-occurring digital addictions are common among vocational students and exhibit graded associations with adverse mental health outcomes. Smartphone addiction appears primarily linked to internalizing distress, while gaming and social media addictions are independently associated with self-harm, underscoring the importance of assessing specific digital activities rather than total screen time.