Abstract
BACKGROUND: Almost one in five (18.8%) UK adolescents are estimated to self-harm and many young people initiate self-harm early (average age 13 years). Prevention of self-harm should be informed by knowledge about risk factors (e.g. socio-demographic indices), characteristics (i.e. motivation for self-harm and help-seeking behaviours), as well as relative aetiological genetic and environmental processes. Previous twin studies evidence both genetic and environmental influences on self-harm. However, to date, there has been no genetically informed research on self-harm aetiology across development, nor studies identifying risk factors for initiating self-harm at a younger age. METHODS: We examined self-harm in the Twins Early Development Study, a birth cohort twin study. Using clustered regression models, we tested associations of socio-demographic factors and victimisation with lifetime self-harm and age of self-harm initiation, both reported at 21. To investigate stability and/or change in genetic and environmental influences on self-harm we interpreted a multivariate Cholesky decomposition across ages ≤16, 21, and 26. RESULTS: Self-harm was more common in adolescence than early adulthood, and the incidence of self-harm in early adulthood was low (1.4%). The most common motivation for self-harm was 'to get relief from a terrible state of mind' (83.4%). Independent predictors of self-harm and earlier initiation of self-harm were being female, belonging to a gender and/or sexual minority group, and experience of bullying victimisation. Sexual minority status was still significantly associated with self-harm after controlling for familial factors in co-twin control analyses. The Cholesky decomposition showed stability in genetic influences and innovation in non-shared environmental influences on self-harm. CONCLUSIONS: Adolescence should be a key period for self-harm interventions. Women, sexual, and gender minorities, and those experiencing victimisation may need targeted support early in adolescence. Furthermore, it should be acknowledged that different individuals can be at risk at different stages as environmental factors influencing self-harm change across time.