Cigarette smoking and Parkinson's disease: a case-control study in a population characterized by a high prevalence of pesticide exposure.

Epidemiological studies have been consistent in showing that cigarette smoking is inversely associated with Parkinson's disease (PD), whereas pesticide use is positively associated with PD. However, the relationship between PD and cigarette smoking remains poorly understood. Our objective was to study the relationship between cigarette smoking and PD in a population characterized by a high prevalence of pesticide exposure. This case-control study was carried out among subjects enrolled in the Mutualite Sociale Agricole, the French health insurance organization for workers connected to the agricultural world. We included 247 cases and 676 controls matched on age, sex, and region of residency. Information on smoking was obtained through in-person interviews. Pesticide exposure was assessed using a case-by-case expert evaluation procedure. We found an inverse relationship between ever cigarette smoking and PD (odds ratio [OR] = 0.6; 95% confidence interval [CI] = 0.4-0.9). The strength of this association increased with the number of pack-years. This relationship was present even when smoking was considered as long as 40 years before PD onset. An inverse association was also present among subjects professionally exposed to pesticides (OR = 0.5; 95% CI = 0.3-0.8) and was independent of the duration of exposure among men. We confirm the inverse association between cigarette smoking and PD in a population characterized by a high prevalence of professional pesticide exposure. The relationship between PD and cigarette smoking was not significantly modified or confounded by exposure to pesticides.