Childhood maltreatment and adolescent non-suicidal self-injury: cross-sectional conditional process and network analyses of depressive symptoms and physical activity.

BACKGROUND: Childhood maltreatment is associated with adolescent non-suicidal self-injury (NSSI), but the roles of depressive symptoms and physical activity remain unclear. We examined these relationships using variable-level and network approaches.

METHODS: This cross-sectional study included 2,354 adolescents recruited by convenience sampling from 30 secondary schools in six Chinese provinces. The 12-item behavior dimension of the Adolescent Non-Suicidal Self-Injury Assessment Questionnaire was the primary outcome. Covariate-adjusted indirect-effect and conditional process analyses used HC3 standard errors and 5,000 bootstrap samples; an 18-node regularized partial-correlation network was also estimated.

RESULTS: Childhood maltreatment correlated positively with depressive symptoms (r = .365) and NSSI behavior (r = .366), while depressive symptoms correlated positively with NSSI behavior (r = .531; all p < .001). Physical activity was negatively associated with depressive symptoms and NSSI behavior. Depressive symptoms showed a significant cross-sectional indirect association between childhood maltreatment and NSSI behavior (effect = .084, 95% bootstrap CI [.072, .098]). The depressive symptoms × physical activity interaction was statistically significant but very small (B = -.015, 95% CI [-.021, -.010]; ΔR2 = .013; f2 = .019), indicating limited practical significance despite the large sample size. Results remained stable after excluding the PHQ-9 self-harm item. Network analysis identified emotional neglect, sleep problems, and physical neglect as prominent positive bridge nodes, while the single NSSI node showed high cross-community connectivity; physical activity showed only weak cross-community connections after accounting for the remaining nodes.

CONCLUSIONS: Depressive symptoms statistically accounted for part of the childhood maltreatment-NSSI association. Although physical activity significantly interacted with depressive symptoms, the interaction explained only 1.3% of additional variance and had limited practical significance. The weak physical activity connections in the network further suggested little unique symptom-level association after shared variance was controlled. Because the data were cross-sectional, temporal mediation and causal inferences cannot be established, and clinical benefit cannot be inferred.