Neuroticism and Non-Suicidal Self-Injury: A Serial Mediation Model of Sleep Disturbance and Cortisol Dysregulation

Background Neuroticism is a robust personality predictor of non-suicidal self-injury (NSSI), a significant public health concern among youth. However, the specific psychobiological mechanisms linking this dispositional trait to self-injurious behavior remain unclear. Sleep disturbance and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis are theoretically plausible mediators, but their sequential role has not been fully elucidated. Objective To test a serial mediation model in which sleep disturbance and cortisol dysregulation sequentially mediate the relationship between neuroticism and NSSI in Chinese youth. Method A cross-sectional survey was conducted with 302 adolescents and young adults. Participants completed self-report questionnaires assessing neuroticism, NSSI, sleep quality, and depressive symptoms. Salivary cortisol was collected over two days to calculate Cortisol Awakening Response (CAR) and Diurnal Cortisol Slope (DCS). Serial mediation analysis was performed, controlling for age, sex, education, and depressive symptoms. Results Neuroticism was positively correlated with NSSI, sleep disturbance, and a flatter DCS, and negatively with the CAR. Neuroticism had both a significant direct effect on NSSI and a significant indirect effect through the serial pathway of sleep disturbance and a blunted cortisol awakening response (Indirect Effect = 0.0008, 95% CI [0.0002, 0.0016]). A similar significant serial indirect effect was found for the diurnal cortisol slope model (Indirect Effect = 0.0007, 95% CI [0.0002, 0.0014]). Conclusions Neuroticism contributes to NSSI risk both directly and indirectly via a psychobiological cascade involving sleep disturbance and HPA axis dysregulation. These findings highlight sleep as a key mechanistic link and a promising target for intervention in high-neuroticism youth.