Sibling bullying in middle childhood and psychotic disorder at 18 years: a prospective cohort study

Background. Being bullied by a sibling has been recently identified as a potential risk factor for developing depression and self-harm. It is unknown whether this risk extends to other serious mental health problems such as psychosis. We investigated whether sibling bullying victimization or perpetration in middle childhood was prospectively associated with psychotic disorder in early adulthood. Methods. The current study investigated 6988 participants of the Avon Longitudinal Study of Parents and Children, a UK community-based birth cohort. Sibling bullying was reported at 12 years and psychotic disorder was assessed via a semi-structured interview at 18 years. Results. Involvement in sibling bullying was associated with psychotic disorder in a dose-response fashion, even after controlling for a range of confounders. Those involved several times a week were 2-3 times more likely to meet criteria for a psychotic disorder [odds ratio (OR); 95% confidence interval (CI)]: victimization (OR 2.74; CI 1.28-5.87); perpetration (OR 3.16; CI 1.35-7.41). Categorical analysis indicated that particularly victims (OR 3.10; CI 1.48-6.50) and bully-victims (OR 2.66; CI 1.24-5.69) were at increased risk of psychotic disorder. Involvement in both sibling and peer bullying had a dose-effect relationship with a psychotic disorder, with those victimized in both contexts having more than four times the odds for a psychotic disorder (OR 4.57; CI 1.73-12.07). Conclusion. Parents and health professionals should be aware of the adverse long-term effects of sibling bullying.