Risk factors for Parkinson's disease.

Parkinson's disease (PD) has been associated with rural living, well-water consumption, and pesticide exposure; however, the individual risk contribution of these variables has not been established. We examined social and medical histories of predominantly rural populations to determine relative risk factors for PD. Patients and controls were surveyed regarding residency, occupation, medical history, and social and dietary habits. An initial multiple logistic regression model was confounded by excessive variable colinearity. Principal factor analysis yielded three factors: rural living (including years of rural residency and ground-water use), pesticide use, and male lifestyle (male gender, head trauma, male-dominated occupations). Other variables did not load in factor analysis and were entered separately, with the three factor scores, in a second multiple logistic regression model. Significant predictors of PD emerged (in order of strength): pesticide use, family history of neurologic disease, and history of depression. The predicted probability of PD was 92.3% (odds ratio = 12.0) with all three predictors positive. Pesticide use (distinguishable from rural living) can be considered a risk factor for the development of PD, with family history of neurologic disease and history of depression serving as weaker predictors of PD.