Occupational exposure in parkinsonian disorders: a 43-year prospective cohort study in men

Our plain-English summary of Occupational exposure in parkinsonian disorders: a 43-year prospective cohort study in men, by A.L. Feldman, A.L. Johansson, G. Nise, et al (Parkinsonism & Related Disorders, 2011).

The study

• Authors: A.L. Feldman, A.L. Johansson, G. Nise, M. Gatz, N.L. Pedersen, K. Wirdefeldt
• Journal: Parkinsonism & Related Disorders
• Published: 2011;17(9):677-82
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Several occupations and occupational exposures have been investigated for associations with Parkinson's disease. Common findings are increased risk associated with pesticide exposure and no association between Parkinson's disease and welding.

Methods: We explored the association between a broad range of possible occupational risk factors and Parkinson's disease as well as Parkinson's disease plus other forms of Parkinsonism (referred to as Parkinsonian disorders), using prospectively collected data in the population-based Swedish Twin Registry. A cohort of 14,169 Swedish men was followed for up to 43 years. We identified 234 Parkinsonian disorder cases including 204 Parkinson's disease cases with complete data. We assessed exposure to 14 chemical and biological compounds through a job exposure matrix. Hazard ratios (HR) with 95% confidence intervals (CI) adjusted for age, smoking, and education were used to estimate the relative risk of disease associated with exposure.

Results: Exposure to inorganic dust was associated with increased risk of Parkinson's disease and Parkinsonian disorders, HR 1.6 (95% CI 1.1-2.4) and 1.5 (1.0-2.2) respectively. There was no association between Parkinson's disease or Parkinsonian disorders and occupational exposure to pesticides, welding smoke, metal dust, wood dust, animal handling, stone and concrete dust, chrome and nickel dust, quartz dust, organic dust, oil, asbestos, organic solvents and irritating gas.

Conclusions: Inorganic dust should be explored further as a potential risk factor for Parkinson's disease. Occupational exposure to pesticides and twelve other compounds explored in this study may not be associated with risk of Parkinson's disease in Swedish men.

Copyright © 2011 Elsevier Ltd. All rights reserved.

In plain English

This prospective cohort study of the Swedish Twin Registry asked whether men's jobs were linked to later Parkinson's disease and to a wider group, Parkinsonian disorders. It followed 20,225 male twins born 1886 to 1947 for up to 43 years, to the end of 2009. Of these, 14,169 had complete data for the main analysis. For the 15,174 men who reported an occupation (main adult occupation for older men, current job for younger men), a job exposure matrix scored the likelihood of exposure to 14 agents, including asbestos. Cases were found through hospital discharge and cause-of-death registers. Men with inorganic dust exposure had a higher risk of Parkinson's disease (hazard ratio 1.6, 95% CI 1.1 to 2.4). This association lost statistical significance after correcting for testing 14 exposures. No association was found for the other 13 exposures. For asbestos-exposed men, the Parkinson's disease hazard ratio was 0.9 (0.6 to 1.4). The authors concluded that inorganic dust should be investigated further. They noted that the matrix gave only the probability of exposure, not the amount, and that power was limited.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective population-based cohort study using a job exposure matrix and register linkage
• Who was studied: 20,225 male twins from the Swedish Twin Registry, born 1886 to 1947, with a mean age of 44.0 years at baseline. Follow-up started in 1967 (men born 1886 to 1925) or 1973 (men born 1926 to 1947) and ran to 31 December 2009. Occupational data were available for 15,174 men (75.0%). Of all the men, 14,169 had complete data on occupation, smoking and education for the adjusted analyses. The study found 336 incident cases of Parkinsonian disorders, including 293 cases of Parkinson's disease; 234 Parkinsonian disorder cases had complete data. Women were excluded because 48.4% had missing occupation data.
• Exposure: Occupation was reported on questionnaires. Men born 1886 to 1925 gave their main occupation in adulthood in 1967; men born 1926 to 1947 gave their present occupation in 1973. Occupational data were available for 15,174 of the 20,225 men. Jobs were scored with a job exposure matrix developed by Karolinska Institutet industrial hygienists for the years 1960 to 1980. The matrix gives the probability of exposure in classes 0 to 3, from under 1 in 10 workers exposed to over 2 in 3 exposed. It does not measure quantity. Fourteen of 29 exposures were analyzed: metal dust, stone and concrete dust, chrome and nickel dust, quartz dust, wood dust, organic dust, inorganic dust, pesticides, animal handling, welding smoke, oil, asbestos, organic solvents and irritating gas.
• Main results:
  • Men with any inorganic dust exposure, compared with unexposed men: hazard ratio 1.6 (95% CI 1.1 to 2.4) for Parkinson's disease and 1.5 (95% CI 1.0 to 2.2) for Parkinsonian disorders. Estimates were adjusted for age, smoking and education.
  • The increased risk was seen for inorganic dust exposure class 1 and for all exposed men. The inorganic dust associations stayed significant after adjusting for 2 comparisons but not after correcting for 14 comparisons (the number of exposures tested).
  • No associations were found between Parkinson's disease or Parkinsonian disorders and any of the other 13 occupational exposures, including asbestos.
  • Men with any asbestos exposure, compared with unexposed men: 35 Parkinson's disease cases, hazard ratio 0.9 (95% CI 0.6 to 1.4); and 36 Parkinsonian disorder cases, hazard ratio 0.8 (95% CI 0.6 to 1.2).
  • For men with class 2 pesticide exposure, the crude incidence rate of Parkinson's disease and Parkinsonian disorders was almost doubled compared with unexposed men. The adjusted hazard ratio showed no association, which the authors attributed to the older age of the exposed men.
  • Current smokers had a lower risk of Parkinson's disease than never smokers (hazard ratio 0.51, 95% CI 0.39 to 0.68).
• The authors' conclusion: The authors concluded that inorganic dust should be investigated further as a potential risk factor for Parkinson's disease. They concluded that the other 13 occupational exposures, including asbestos, were not associated with Parkinson's disease or Parkinsonian disorders and may not be associated with risk in Swedish men.
• Limitations the authors state:
  • The job exposure matrix is not perfectly sensitive, which could bias results toward finding no effect.
  • The matrix gives only the probability of exposure for each occupation, not quantitative levels, so a dose-response relationship could not be assessed.
  • The matrix gives no details about exposure to specific environmental compounds.
  • There were no data on recreational exposures.
  • Because cases came from hospital and death records, severe cases or cases with other serious illness may be over-represented. The authors argued that this bias was non-differential with regard to exposure.
  • The limitations may have produced false negative findings, and power to detect an association for pesticide exposure was limited.
  • There were no full occupational histories. Only one occupation per man was recorded, and the younger twins may have changed jobs after data collection.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Cohort Study, Hazard Ratio, confidence interval, Relative Risk.

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