http://www.sciam.com/article.cfm?alias=smoking-lowers-parkinsons&chanId=sa003
Smoking lowers Parkinson's disease risk
Smoking lowers Parkinson's disease risk
Compared to people who had never smoked and were considered to have "normal" Parkinson's disease risk, former smokers had a 22-percent lower risk of Parkinson's disease and current smokers had a 73-percent lower risk.
The results of our study," Thacker said, "can probably be explained by something in cigarettes -- most likely in the tobacco itself -- actually protecting people against getting Parkinson's disease. That would be the simplest explanation that makes the most sense."