Role of homelessness and psychiatric disorders in suicide deaths among veterans: A four-way decomposition analysis.

Homelessness and suicide are top priorities in the U.S. Department of Veterans Affairs (VA). This study examined the various pathways involving homelessness, substance use, and mental health disorders in relation to suicide deaths among veterans in the VA healthcare system. A retrospective cohort study was conducted among 6,128,921 veterans-399,125 homeless and 5,729,796 non-homeless-followed-up between 2017 and 2021 using VA/Department of Defense linked databases. Multivariable Cox regression was applied for homelessness and psychiatric disorders as predictor of suicide deaths, sequentially controlling for demographic, clinical, substance use, and mental health characteristics. Four-way decomposition analysis was used to calculate proportions of suicide deaths mediated and/or moderated by homelessness, substance use, and mental health disorders. The relationship between homelessness and suicide-specific mortality risk was reduced from 40 % greater risk in unadjusted to 9 % greater risk in fully-adjusted models. Nearly 26 % of the total effect of homelessness on suicide-specific mortality risk was mediated by substance use disorders, whereas 49 % was mediated and 36 % was moderated by mental health disorders. In conclusion, excess suicide-specific mortality risk in homeless veterans is partly explained by substance use and mental health disorders, highlighting the importance of wrap-around health and social services for homeless veterans in mitigating suicide risk.