Abstract
BackgroundThe etiology of Parkinson's disease (PD) remains unclear, and environmental risk-factors such as occupation have attracted interest.ObjectiveThe goal was to investigate occupational complexity in relation to PD.MethodsWe conducted a population-based cohort study based on the Swedish Twin Registry that included 28,778 twins born between 1886 and 1950. We identified 433 PD cases during the study period. Data on occupation were collected from either the 1970 or 1980 Swedish census, and occupational complexity was assessed via a job exposure matrix. Cox proportional hazard regression analyses with age as the underlying time scale were used to assess PD risk as a function of the three domains of occupational complexity: data, people, and things. Sex and smoking were included as covariates. Analyses stratified by twin pair were conducted to test for confounding by familial factors.ResultsHigh occupational complexity with data and people was associated with increased risk overall (Hazard Ratio [HR] = 1.07, 95% confidence interval [CI] 1.02–1.14, and HR = 1.10, 95% CI 1.01–1.21, respectively), and in men (HR = 1.08, 95% CI 1.01–1.16, and HR = 1.15, 95% CI 1.03–1.28, respectively). Complexity with things was not associated with risk of PD. When the analyses were stratified by twin pair, the HRs for occupational complexity with data and people were attenuated in men.ConclusionsHigh complexity of work with data and people is related to increased risk of PD, particularly in men. The attenuation of risk observed in the twin pair-stratified analyses suggests that the association may partly be explained by familial factors, such as inherited traits contributing to occupational selection or other factors shared by twins.
Highlights
Parkinson’s disease (PD) is the second most common neurodegenerative disorder in adults aged 60 and older [1]
The attenuation of risk observed in the twin pair-stratified analyses suggests that the association may partly be explained by familial factors, such as inherited traits contributing to occupational selection or other factors shared by twins
We expected that any results would be attenuated in the twin pair analyses compared to the analyses with the entire sample, suggesting that familial factors such as inherited traits contributing to occupational selection or other factors shared by twins potentially underlie the results
Summary
Parkinson’s disease (PD) is the second most common neurodegenerative disorder in adults aged 60 and older [1]. With the continued growth of the older adult population, PD prevalence in people over age 50 is expected to double from between 4.1 and 4.6 million in 2005 to between 8.7 and 9.3 million by 2030 in 15 of the world’s most populous nations [2]. Etiology of PD is likely influenced by both environmental and genetic factors. Data from several studies suggest that environmental factors may be more important than genetic factors in risk of PD [3]. The etiology of Parkinson’s disease (PD) remains unclear, and environmental risk-factors such as occupation have attracted interest. Characteristics Age at baseline, years Time to end of follow-up, years Women Current smoker (baseline) Occupational Complexity Data People Things doi:10.1371/journal.pone.0106676.t002 Min Max. Non-Parkinson’s Disease (N = 28,345) Mean SD.
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