Objectives Sunlight is the main contributor to vitamin D in humans. Since inadequate levels of vitamin D have been linked to increased risks for neurodegenerative diseases, we examined whether outdoor work is associated with a reduced risk for Parkinson's disease in a population-based case–control study of Danish men.
Methods We identified 3819 men with a primary diagnosis of Parkinson's disease in the period 1995–2006 in the Danish National Hospital Register and selected 19 282 age- and sex-matched population controls at random from the Central Population Register. Information on work history was ascertained from the Danish Supplementary Pension Fund and the Central Population Register. Based on trade grouping codes and job titles, we evaluated the extent of outdoor work of study subjects as a proxy of exposure to sunlight.
Results Relying on trade grouping codes, we estimated ORs for study subjects with moderate, frequent and maximal outdoor work compared with exclusive indoor work of 0.90 (95% CI 0.78 to 1.02), 0.86 (95% CI 0.75 to 0.99) and 0.72 (95% CI 0.63 to 0.82), respectively, for Parkinson's disease. Reduced risks were also found for Parkinson's disease among outdoor workers based on study subjects' job titles.
Conclusions Our findings suggest that men working outdoors have a lower risk for Parkinson's disease. Further studies of measured vitamin D levels in outdoor workers are warranted to clarify a potential inverse association between vitamin D and the risk for Parkinson's disease.
- Parkinson's disease
- case-control studies
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Funding This study was supported by a grant from the National Institutes of Health, USA (grant no. R01 ES013717). The funding source had no role in the design and conduct of the study or in the collection, management, analysis, and interpretation of the data or with preparation, review, or approval of the manuscript.
Competing interests None.
Ethics approval The study protocol was approved by the Danish Data Protection Agency (no. 2002–41–2112) and the University of California at Los Angeles institutional review board for human subjects.
Provenance and peer review Not commissioned; externally peer reviewed.