JMIR Publications

ABSTRACT

Background:

The impact of smartphone use on mental health is being rigorously debated. Some questionnaire-based research suggests that smartphone use correlated with non-suicidal self-injury (NSSI), self-reported data seem unlikely to capture smartphone use precisely, requiring objective measures to advance this field.

Objective:

To examine whether objectively measured smartphone use was associated with NSSI in college students.

Methods:

This multicenter cross-sectional study was conducted from 2022 to 2024, enrolling college students from 559 classes within 6 universities in China. NSSI was measured by the Ottawa Self-Injury Inventory (OSI) including 10 items of NSSI without suicidal intent within the past month. Participants answering “ever” were deemed to have NSSI. Objectively measured smartphone screen time and number of smartphone unlock were obtained from smartphone use records screenshots. The association between objectively measured smartphone use and NSSI was analyzed using binary logistic regression models and restricted cubic splines regression.

Results:

Of 16668 participants included in the analyses, 627 (3.8%) participants reported engaging in NSSI. The mean (SD) smartphone screen time and number of smartphone unlock were 48.8(28.8) h/week and 271.6(291.0) times/week. The models adjusted for different factors showed that smartphone use was associated with NSSI. Compared to participants with 0-21 h/week of smartphone screen time, those with ≥63 h/week of smartphone screen time had a higher odds of NSSI (OR=1.63; 95% CI, 1.32-2.01). Likewise, compared to participants with 0-50 times/week of smartphone unlock, those with ≥400 times/week of smartphone unlock had a higher odds of NSSI (OR=1.53; 95% CI, 1.25-1.88). Smartphone screen time <63 h/week or smartphone unlock number <400 times/week had no association with NSSI. Moreover, the increasing risk of NSSI was associated with an increasing smartphone screen time and smartphone unlock number.

Conclusions:

These findings emphasize that smartphone screen time ≥63 h/week and ≥400 times/week of smartphone unlock are risk factors for NSSI in college students, interventions targeting NSSI should consider the apparent association with smartphone use.