Religious switching and mental disorders in young adulthood: evidence from Finnish population register data.

This is the first study to analyze religious switching and sickness allowance (SA) due to mental disorders using register data with ICD-codes. We performed a prospective cohort study based on population born in Finland in 1986-2003 (n = 1 060 280). Each person was observed from age 18 in 2004-2023. Cox proportional hazards models with and without sibling fixed effects, and logistic regression models restricted to individuals who had switched religion, were applied. We observed a 44% higher hazard of SA receipt of non-affiliated individuals, and a 27% higher hazard for those with any other religion, as compared to the majority group of Lutherans at a time point when they had not switched religion. Religious switching was associated with a 38%-118% higher hazard of SA receipt, depending on the type of switch. Results from models with and without sibling fixed effects were similar. The conditional logistic regressions revealed that, the increase in mental health-related SA receipt was steeper before the switch as compared to after the switch. However, the incidence of mental health problems remained elevated after religious switching. These findings suggest that religious switching and poor mental health are interrelated, and that the direction of causality may run in both directions.