Parkinson's disease and history of outdoor occupation.

Background: Human and animal studies, albeit not fully consistent, suggest that vitamin D may reduce risk of Parkinson's disease (PD). Ultraviolet radiation converts vitamin D precursor to the active form. This study examined the hypothesis that working outdoors is associated with a decreased risk of PD.

Methods: PD cases were enrolled from Group Health Cooperative, a health maintenance organization in the Puget Sound region in western Washington State, and the University of Washington Neurology Clinic in Seattle. Participants included 447 non-Hispanic Caucasian newly diagnosed PD cases diagnosed between 1992 and 2008 and 578 unrelated neurologically normal controls enrolled in Group Health Cooperative, frequency matched by race/ethnicity, age and gender. Subjects' amount of outdoor work was estimated from self-reported occupational histories. Jobs were categorized by degree of time spent working outdoors. A ten-year lag interval was included to account for disease latency. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression, with adjustment for age, gender, and smoking.

Results: Outdoor work was inversely associated with risk of PD (outdoor only compared to indoor only): OR = 0.74, 95% CI 0.44-1.25. However, there was no trend in relation to portion of the workday spent laboring outdoors and PD risk.

Conclusion: Occupational sunlight exposure and other correlates of outdoor work is not likely to have a substantial role in the etiology of PD.