Smokers have a lower risk of developing Parkinson's disease than nonsmokers, and the protective effects appear to decline when smokers quit, according to researchers from the Harvard School of Public Health.

Reuters reported March 20 that the study of more than 140,000 men and women found that current smokers had a 73-percent lower risk of developing Parkinson's than nonsmokers, while former smokers had a 22-percent lower risk. How long subjects smoked and how long it had been since they had quit seemed to have more impact on risk protection than how much they smoked each day.

"It is not our intent to promote smoking as a protective measure against Parkinson's disease," said lead researcher Evan L. Thacker. "Obviously smoking has a multitude of negative consequences. Rather, we did this study to try to encourage other scientists ... to consider the possibility that neuroprotective chemicals may be present in tobacco leaves."

"The observation that smokeless tobacco users also have a lower risk of Parkinson's disease suggests that the most likely candidates are not compounds generated by combustion, but rather constituents of the tobacco leaves," he added.

The study was published in the March 6, 2007 issue of the journal Neurology.