Background
People experiencing homelessness die 20 years earlier than other people and preventive action to counteract this are unknown. We aimed to study the association between homelessness and the risk of suicide and self-harm considering psychiatric disorders compared with the general population.
Methods
We did a national, register-based cohort study of people living in Denmark between Jan 1, 1999, and Dec 31, 2020, and born between 1945 and 2006 aged 15 years and older. The study population was drawn from the Danish Civil Reigstration System, which was linked to other population-based registers. The outcomes were first episode of self-harm and death from suicide. We calculated incidence rates (IRs) per 100,000 person-years at risk, incidence rate ratios (IRRs) using Poisson regression analysis and estimated the probability of both outcomes by calculating the cumulative incidence. IRRs stratified by sex and adjusted for calendar year, socio-demographic factors, and psychiatric disorders.
Findings
The study cohort included 5,261,751 Danish residents aged 15-75 years living between Jan 1, 1999, and Dec 31, 2020, contributing with 82,673,485 person-years at risk. Overall, 9858 (0.2%) individuals died from suicide and 88,645 individuals had at least one episode of self-harm. In all, 57,069 individuals experienced homelessness with 690 (1.1%) deaths from suicide. In people experiencing homelessness, after five years, the probability of self-harm was 6.9% in women and 6.3% in men (aIRR of self-harm associated with homelessness was 3.3 (95% CI 3.1-3.5) in women and 3.5 (3.4-3.6) in men compared with the general population). aIRR of suicide was 3.8 (95% CI 3.2-4.4) in women and 2.2 (95% CI 2.0-2.4) in men epxeriencing homelessness compared with the general population. Men experiencing homelessness who also had a history of self-harm had lower IRR of suicide (7.4, 95% CI 6.5-8.5) than men with a history of self-harm only (9.8, 95% CI 9.2-10.4) compared with men without both. Women experiencing homelessness with a history of self-harm had higher IRR (17.4, 95% CI 14.2-21.4) than women with a history of self-harm only (12.9, 95% CI 11.7-14.1).

Conclusions

Homelessness predicts suicide and self-harm. In people presenting with self-harm, homelessness only adds additional risk of suicide in women, not in men. These results suggest a need for prevention of homelessness and efforts to address the high rates of self-harm in people experiencing homelessness.