How do the prevalence and relative risk of non-suicidal self-injury and suicidal thoughts vary across the population distribution of common mental distress (the p factor)? Observational analyses replicated in two independent UK cohorts of young people.

OBJECTIVES: To inform suicide prevention policies and responses to youths at risk by investigating whether suicide risk is predicted by a summary measure of common mental distress (CMD (the p factor)) as well as by conventional psychopathological domains; to define the distribution of suicide risks over the population range of CMD; to test whether such distress mediates the medium-term persistence of suicide risks. DESIGN: Two independent population-based cohorts. SETTING: Population based in two UK centres. PARTICIPANTS: Volunteers aged 14-24 years recruited from primary healthcare registers, schools and colleges, with advertisements to complete quotas in age-sex-strata. Cohort 1 is the Neuroscience in Psychiatry Network (n=2403); cohort 2 is the ROOTS sample (n=1074). PRIMARY OUTCOME MEASURES: Suicidal thoughts (ST) and non-suicidal self-injury (NSSI). RESULTS: We calculated a CMD score using confirmatory bifactor analysis and then used logistic regressions to determine adjusted associations between risks and CMD; curve fitting was used to examine the relative prevalence of STs and NSSI over the population distribution of CMD. We found a dose-response relationship between levels of CMD and risk of suicide. The majority of all subjects experiencing ST and NSSI (78% and 76% in cohort 1, and 66% and 71% in cohort 2) had CMD scores no more than 2 SDs above the population mean; higher scores indicated the highest risk but were, by definition, infrequent. Pathway mediation models showed that CMD mediated the longitudinal course of both ST and NSSI. CONCLUSIONS: NSSI and ST in youths reflect CMD that also mediates their persistence. Universal prevention strategies reducing levels of CMD in the whole population without recourse to screening or measurement may prevent more suicides than approaches targeting youths with the most severe distress or with psychiatric disorders.The ROOTS study was supported by a Wellcome Trust Grant (Grant number 074296) to I.M.G. and P.B.J., the NIHR Collaborations for Leadership in Applied Research and Care (CLAHRC) East of England, and the NIHR Cambridge Biomedical Research Centre. The NSPN study was supported by the Wellcome Trust Strategic Award (095844/Z/11/Z) to I.M.G., E.B., P.B.J., R.D., P.F. The work has been carried out in the Department of Psychiatry, University of Cambridge. We wish to thank the NSPN and ROOTS participants and Dr Golam Khandaker for his comments and NSPN Consortium (see the list of members in the Supplement)