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Occupation and Risk of Parkinsonism
Archives of Neurology 9/14/2009
Caroline M. Tanner, MD, PhD; G. Webster Ross, MD; Sarah Jewell, MD, MPH; Robert A. Hauser, MD; Joseph Jankovic, MD; Stewart A. Factor, DO; Susan Bressman, MD; Amanda Deligtisch, MD; Connie Marras, MD, PhD, FRCPC; Kelly Lyons, PhD; Grace S. Bhudhikanok, PhD; Diana F. Roucoux, MPH; Cheryl Meng, MS; Robert D. Abbott, PhD; J. William Langston, MD.
Background
A combination of genetic and environmental factors are thought to cause Parkinson’s disease, although much more research is needed to identify the key risk factors. Previous research reports have suggested that exposure to toxic chemicals - including pesticides, solvents and metals - may contribute to the neurodegenerative disease process. Some studies have also found that working in specific occupations – including agriculture, education, health care, welding and mining – may increase the risk of parkinsonism. This study was designed to evaluate whether working in certain occupations or exposure to specific toxicants was associated with the risk of being diagnosed with Parkinson’s disease or other types of parkinsonism.
Design
This was a case-control study, in which the characteristics and occupational history of people with a diagnosis of parkinsonism (cases) were compared to those of people without parkinsonism (controls). Approximately 500 cases and 500 controls were enrolled in the study from eight North American clinics specializing in movement disorders; this helped to ensure the accuracy of thediagnosis of parkinsonism. The control participants were chosen to match the cases with regard to age, sex and location so that the comparisons would be done between similar groups of people. Each participant was interviewed extensively via a very detailed telephone interview lasting several hours. The standardized questionnaires covered lifelong history of possible factors affecting the risk for parkinsonism, including use of tobacco, alcohol and caffeine, head injury and occupation (all jobs held for at least three months). For each job, detailed information about the industry, processes, tasks and materials was collected. All of the work-related information was reviewed and standardized occupational codes were assigned for each job. These results were then analyzed using statistical models that took multiple factors into account, including age, sex, race/ethnicity, smoking, caffeine and alcohol consumption and head injury. Only exposures which occurred before diagnosis (or before a reference date for control participants) were included in the analysis.
Results
People with a history of tobacco use had a decreased risk of parkinsonism, a finding that has been consistently reported in earlier studies. The study participants worked in a variety of occupations, including those reported elsewhere to be associated with parkinsonism, but we did not find increased disease rates in participants who had done work in farming, healthcare, education or welding (no miners were enrolled in our study). The risk of parkinsonism was increased for work in legal, construction/extraction and religious sectors, and decreased for workers in personal care/service, food preparation and some military duties. However, these risks were not increased or decreased when the length of the job was taken into account. In analyzing specific work tasks and exposures, we did not find that any of the following were linked to parkinsonism risk: woodworking, gluing, welding, soldering, cleaning with solvents, painting, stripping wood or paint or machining. However, the risk of parkinsonism did increase with pesticide use. The odds of having parkinsonism were 1.9 times higher in participants who had used any pesticides, 2.2 times higher if at least one of eight suspect pesticides was used and 2.6 times higher among those who had used 2,4-dichlorophenoxyacetic acid (2,4-D). Two others pesticides, permethrin and paraquat, were also associated with higher risk of parkinsonism, but the association was less certain statistically. The duration of pesticide use did not affect the odds of disease, but there were few long-term pesticide users enrolled in this study. None of the occupations, job tasks or exposures were associated with having atypical parkinsonism (vs. typical Parkinson’s disease), or with having a younger age at diagnosis. No job tasks or exposures increased the risk of the clinical subtype of parkinsonism with postural instability and gait difficulty.
Conclusion
The finding that parkinsonism risk is increased with pesticide use joins a growing body of evidence that environmental and occupational toxicant exposure can be a significant risk factors of Parkinson’s disease.