Increased risk of Parkinson's disease after depression - A retrospective cohort study

Background: Depression has been linked to the occurrence of a number of somatic diseases. There are no data for PD. Objective: To determine if depression is associated with a subsequent risk for PD. Methods: A retrospective cohort study design based in general practice was applied. All subjects diagnosed with depression between 1975 and 1990 were included and matched with subjects with the same birth year who were never diagnosed with depression. Follow-up ended at April 30, 2000. Hazard ratios (HR) and 95% CI were calculated using Cox proportional hazards models adjusted for age, sex, and socioeconomic status. Subgroups based on sex and age at diagnosis of depression were evaluated separately. Results: Among the 1,358 depressed subjects, 19 developed PD, and among the 67,570 nondepressed subjects, 259 developed PD. The HR (95% CI) for depressed vs nondepressed subjects was 3.13 (1.95 to 5.01) in multivariable analysis. Associations in subgroups were comparable with the overall association. Conclusion: A strong positive association was found between depression and subsequent incidence of PD.