Risk of Parkinson disease in agricultural occupations in Finland

Abstract

Introduction Prior epidemiologic studies indicate that agricultural work and occupational exposure to pesticides may increase risk of Parkinson disease (PD). Findings may vary by country as well as by type and degree of agricultural exposures. We therefore studied whether work in agriculture, forestry, and fishing is related to the risk of PD in Finland. Methods We constructed a population-based case-control study of incident PD in Finland using a medication register maintained by the Social Insurance Institution of Finland, along with the Population Information System, which includes census records for all Finnish residents. PD cases were diagnosed (first approved to receive symptomatic therapy for PD) between 1995–2014. We randomly selected two controls per case from the general population while matching on diagnosis year, birth year (1930–1950), and sex. Individual occupational census data from 1990, allowing for a minimum of four years of exposure lagging, was used to define occupation. We included 36,398 economically active subjects (12,204 PD cases and 24,194 controls). We linked the data on occupation in 1990 to the Finnish Job Exposure Matrix (FINJEM) to identify potential for occupational exposure to pesticides and other FINJEM agents. We estimated matching variable adjusted odds ratios (ORs) and more fully adjusted odds ratios (aOR), and 95% confidence intervals (CIs) using logistic regression while respectively adjusting for matching variables only, or also for socioeconomic status and any environmental tobacco smoke at work (ETSW). Environmental tobacco smoke, including ETSW, appears to be inversely associated with PD, while socioeconomic status is likely associated with active tobacco smoking, which is well established as strongly inversely associated with PD. Results In total, 1797 PD cases (14.7%) and 3224 controls (13.3%) were working in agricultural occupations in 1990, suggesting a modestly increased risk of PD (OR 1.12; CI: 1.05–1.19 and aOR 1.13; CI: 1.03–1.24). The majority were farmers or doing any type of managerial work in agriculture (1529 PD cases, 2692 controls, aOR 1.17; CI: 1.05–1.30). We also observed a greater PD risk among workers in agriculture, horticulture and animal husbandry (147 PD cases, 260 controls, aOR 1.18; CI: 0.96–1.46). In contrast, there was no indication of a greater risk of PD in other agricultural occupational groups: aOR 0.67; CI: 0.37–1.19 for “fishermen/fish farmers” (15 PD cases, 48 controls) and aOR 0.98; CI: 0.77–1.24 for “forestry workers/lumberjacks” (106 PD cases, 224 controls). Exposure to insecticides, herbicides and fungicides were highly correlated with agricultural occupations, and yielded ORs relatively similar to the overall estimate for agricultural occupation. Conclusion We observed a modest positive association between agricultural occupations and PD in Finland. However, it is possible that this association at least in part is related to a known relatively low prevalence of active tobacco smoking among most agricultural workers in Finland outside of fishing and forestry as compared to the general population.