Environmental risk factors in Parkinson's disease.

We studied the environmental risk factors of Parkinson's disease (PD) in Finland, particularly those related to rural environment, in a prevalence material in 1992. The population numbered 196,864 people, including urban and rural areas. In this community-based study, we used a case-control method with personal investigation of the case subjects (n = 123) and matched control subjects (n = 246). Analyses were carried out by conditional logistic regression model. Case subjects had far fewer domestic animals at home during their lifetime, including cows, sheep, pigs, and chickens. The difference was even more obvious in those under the age of 20 years, including also cats and horses, but diminished after 20 years. The number of different animal species was smaller with case subjects as was the duration of animal contacts. Case subjects found their work physically heavier and exercised more. The mean age at onset in ever-smoking men was significantly higher than in never-smoking men. No special reason for non-smoking increased, and a physical reason decreased the risk of PD. Area of birth or living, farming and other occupations, types of drinking water, pesticide and herbicide use, head injuries, use of alcohol, education, and carbon monoxide poisonings were similar among case subjects and control subjects. In conclusion, domestic animals, or something that is connected with the animals, may have a protecting effect against PD. Alternatively, the observed negative associations of domestic animals at home and subsequent PD may only be a marker of other environmental conditions or lifestyles.