Area-level socioeconomic deprivation and suicide by household income: a nationwide cohort study 2015–23

Background Although area-level socioeconomic deprivation is a potential target for suicide prevention, it remains unclear whether its impact varies by individual socioeconomic status. We investigated whether the association between area-level socioeconomic deprivation and suicide differs by household income. Methods This nationwide cohort study included working-age individuals (18–74 years) covered by the Japan Health Insurance Association from April 2015 to March 2023. Area-level socioeconomic deprivation was assessed at the municipality level by using the Area Deprivation Index in Japan. The incidence rate ratio (IRR) of suicide by area-level socioeconomic deprivation was estimated according to household-income levels. The IRR was adjusted for age, sex, enrollment year, family structure, histories of physical diseases and psychiatric disorders, urbanicity, and local medical resources. Probabilistic bias analysis was applied to provide a bias-adjusted estimate with its uncertainty. Results Among 39 432 793 individuals (57.9% men; mean age 42.9 years), 6508 died by suicide. Area-level socioeconomic deprivation was associated with higher suicide risk, independently of covariates [IRR = 1.11, 95% confidence interval (CI) 1.05–1.17]. This association was found in both the high-household-income group (IRR = 1.12, 95% CI 1.05–1.20) and the low-household-income group (IRR = 1.10, 95% CI 1.02–1.18), with no evidence of heterogeneity. Probabilistic bias analysis supported these findings. Conclusion People in deprived areas experienced higher suicide risk, without heterogeneity by household income. Limitations include potential outcome misclassification, as approximately one-third of cause-of-death data were missing. Addressing area-level socioeconomic deprivation may prevent suicide, regardless of individual socioeconomic status.