Abstract
BACKGROUND: Family adversity and childhood abuse have been associated with an increased risk of homelessness in adulthood. However, to our knowledge, no population-based longitudinal studies have examined the association between out-of-home placement and subsequent homelessness, while accounting for psychiatric disorders and parental background. Thus, we aimed to investigate the association between out-of-home placement and psychiatric disorders during childhood or adolescence and homelessness later in life. METHODS: We used data from a nationwide, register-based birth cohort in Denmark from 1 January 1983 to 31 December 2003, who were alive at any point from 1 January 2001 to 31 December 2021. Children and adolescents (aged 0-17) were followed up from their 18th birthday for risk of homelessness. We investigated associations using national registers with information on homelessness and psychiatric disorders. We examined individuals with any out-of-home placement history with and without psychiatric disorders diagnosed up to age 18 according to the first episode of homelessness after age 18, defined as first contact with a shelter. We estimated the cumulative incidence function using an Aalen-Johansen estimator. Hazard ratios (HRs) for the association between out-of-home placement, psychiatric disorder, and homelessness were estimated by sex using Cox proportional-hazard regression analyses, adjusted for birth year, parental sociodemographic factors and psychiatric disorders. Additionally, we employed a stratified Cox model (stratified by mother) to examine the contribution of within-family covariates. FINDINGS: The study cohort included 1,226,130 Danish residents aged 18-39 years. Of these, 53,281 individuals (4·3%) had experienced out-of-home placement during childhood or adolescence. By age 39, 12·2% (95% CI 11·6-12·7) of males and 6·3% (95% CI 5·9-6·7) of females with a history of out-of-home placement experienced homelessness. This corresponds to a substantially increased risk compared to people without such a history, with adjusted HRs of 7·1 (95% CI 6·7-7·5) for males and 9·0 (8·2-9·8) for females. In sibling analyses restricted to 955,287 individuals and adjusted for birth year, out-of-home placement was associated with a 3-fold increased risk of homelessness compared to siblings without such a history (aHR 2·8 (95% CI 2·4-3·3) for males and aHR 3·2 (2·4-4·1) for females). Homelessness risk was even higher for individuals with a history of both out-of-home placement and psychiatric disorder, particularly when psychiatric diagnosis occurred after the first placement. In the full cohort, adjusted HRs were 11·8 (95% CI 10·8-13·0) for males and 19·3 (16·9-21·9) for females, compared to individuals with neither out-of-home placement nor psychiatric disorder. INTERPRETATION: Individuals with a history of out-of-home placement are at higher risk of experiencing homelessness, particularly those with co-occurring psychiatric disorders. These findings highlight the need for targeted interventions and coordinated efforts across medical and social services to prevent homelessness. FUNDING: Funded by a grant from the Lundbeck Foundation to SFN, F-61171-23-50 and the Independent Research Fund to SFN 10.46540/3162-00051B.