Sex differences in self-harm and suicide in young autistic adults

Introduction
Both suicide and self-harm are disproportionately common in autistic people. Sex differences in risk of self-harm and suicide are observed in the general population, but findings are mixed for autistic people. Self-cutting may be a particularly risky self-harm behaviour for suicide in autistic people. We aimed to explore sex differences and differences in method of self-harm in the association between self-harm and suicide in autistic and non-autistic adolescents and young adults.

Methods
We used a total population register of 2.8 million Swedish residents. Participants were followed from age 12 until December 2021 for medical treatment because of self-harm, and death from suicide. We used Cox proportional hazard regression models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of death from suicide following self-harm, and Relative Excessive Risk due to Interaction (RERI) to explore the interaction between self-harm and autism in females and males.

Results
We identified 85,143 autistic individuals (31,288 female; 53,855 male) and 2,628,382 non-autistic individuals (1,286,481 female; 1,341,901 male) aged 12–37 years. Incidence of suicide following self-harm was higher in autistic males (incidence per 100,000 risk-years = 169.0 [95% CI 135.1, 211.3]) than females (125.4 [99.4, 158.3]). The relative risk was higher for autistic females (HR 26.1 [95% CI 20.2, 33.7]) than autistic males (12.5 [9.9, 15.8]). An additive effect of both autism and self-harm was observed in both females (RERI = 9.8) and males (2.0). Autistic individuals who self-harmed through cutting were at greatest risk of death from suicide (HR 25.1 [17.9, 35.2]), compared to other methods.

Conclusion
Autistic males and females are at increased risk of death from suicide following severe self-harm, particularly self-cutting.