Psychiatric disease incidence among Danish Seventh-day Adventists and Baptists

Purpose: Previous studies suggest that religious practice can have a positive effect on mental health, but may also have potential for harm. In Denmark, unique possibilities are available for studying the influence of religious practice on mental health: Denmark is characterized as a secular society and it is possible to follow members of religious societies in nationwide registers. In this study, we follow a cohort of Danish Seventh-day Adventists (SDA) and Baptists in a nationwide psychiatry register and compare the incidence in this cohort with the general population. Methods: We followed a cohort of 5,614 SDA and 3,663 Baptists in the Danish Psychiatric Central Register, which contained information on psychiatric hospitalizations from 1970 to 2009. Psychiatric disease incidence in the cohort was compared with that in the general Danish population as standardized incidence ratios and within-cohort comparisons were made with a Cox model. Results: The cohort had decreased incidence of abuse disorders compared to the general population. Furthermore, among Baptists, decreased incidence of unipolar disorders among men and decreased incidence of schizophrenia among women were observed. Surprisingly, we observed an increased incidence rate of unipolar disorder among women. Conclusions: In this nationwide cohort study with 40 years of follow-up, we observed increased incidence rates of unipolar disorders among women and decreased rates of alcohol- and drug-related psychiatric disorders compared to the general Danish population. We have no mechanistic explanation for the increased incidence of unipolar disorders among women, but discuss several hypotheses that could explain this observation.