Associations of excessive smartphone duration and unlock frequency with non-suicidal self-injury in college students

BACKGROUND The mental health impact of smartphone use remains incompletely understood. Although several prior studies have suggested a correlation between smartphone usage and non-suicidal self-injury (NSSI), reliance on self-reported data limits the accuracy of exposure assessment. Objective measurements are needed to elucidate this relationship better. AIM To examine the associations of objectively assessed smartphone duration and unlock frequency with NSSI. METHODS This cross-sectional study included 17851 college students from China. NSSI was assessed using the Ottawa Self-Injury Inventory, which includes ten NSSI behaviors. Smartphone duration and unlock frequency were objectively monitored through participant-submitted screenshots. Binary logistic and restricted cubic spline models were used for analyses. RESULTS Of 17851 participants, 460 (2.6%) exhibited NSSI in the past month. The mean (SD) weekly smartphone duration and unlock frequency were 49.1 (29.9) hours and 390.9 (278.2) times. After adjusting for sociodemographic characteristics, health-related behaviors, and negative life events, smartphone use was significantly and positively associated with NSSI. Compared to students with 0-21 hours/week of smartphone duration, those with ≥ 63 hours/week exhibited a significantly higher risk (odds ratio = 1.60; 95% confidence interval: 1.23-2.11). Similarly, compared to students with 0-50 times/week of smartphone unlock frequency, those with ≥ 400 times/week (odds ratio = 1.48; 95% confidence interval: 1.11-2.00) had significantly higher NSSI risk. Restricted cubic spline analyses confirmed a monotonic increase in NSSI risk with increasing smartphone duration (P value for non-linear = 0.971) and unlock frequency (P value for non-linear = 0.225). CONCLUSION Excessive smartphone duration and unlock frequency are associated with an elevated risk of NSSI among college students, underscoring the need to consider smartphone use behaviors in NSSI prevention.