Student Research: Elena Kwon

, Occupational and Environmental Medicine (OEM), 2012
Faculty Advisor:

Outdoor Occupational History and Risk of Parkinson Disease: a Case-Control Study


Abstract

Introduction: A role for antioxidants in prevention of Parkinson disease has been proposed, however, epidemiologic evidence supporting this assertion has been inconclusive. Ninety percent of vitamin D in adults is produced in vivo related to ultraviolet type B exposure. This creates a plausible role for outdoor work as a strong surrogate for vitamin D in studies related to neurodegenerative disease.

Design and Setting: We investigated this association among non-Hispanic Caucasians in Washington state using 447 incident Parkinson disease cases diagnosed between 1992-2008, and 578 neurologically normal controls, frequency matched by age and sex.

Material and Methods: Subjects' work histories were obtained by in-person interviews, and a validated method was used to classify each occupation up to 10 years prior to diagnosis (cases)/reference (controls) according to relative time spent outdoors. Research participants were categorized as having exclusively indoor, a combination of indoor/outdoor, or exclusively outdoor occupations using job title. Length of time employed in each occupation was also used to estimate the lifetime duration of any outdoor work, and the maximal and typical levels of outdoor work.

Results: Classified by job title and without the inclusion of a 10-year lag time, Odds ratios and 95% confidence intervals from unconditional logistic regression adjusting for age, sex, and smoking were as follows: (> 0 - < 50% of work day outdoors) 0.79 (0.50-1.22), (50%-75% workday outdoors) 0.81 (0.52-1.25), and (> 75% workday outdoors) 0.86 (0.60-1.23), compared to workers who labored exclusively indoors. Classified by job title and incorporating a 10-year lag time, Odds ratios and 95% confidence intervals from unconditional logistic regression adjusting for age, sex, and smoking were as follows: (> 0 - < 50% of work day outdoors) 0.85 (0.54-1.32), (50%-75% workday outdoors) 0.83 (0.54-1.29), and (> 75% workday outdoors) 0.85 (0.60-1.22), compared to workers who labored exclusively indoors.

Conclusions: Our findings suggest that workers who spend at least part of their day outdoors have a lower risk of Parkinson disease as compared to workers who labor exclusively indoors. This supports the hypothesis that ultraviolet type B exposure acting as an ecological surrogate for vitamin D may provide a protective effective for the development of Idiopathic Parkinson Disease.