A study in Swedish twins confirms that smoking is associated with a reduced risk of Parkinson’s disease .

“The association in part is explained by genetic influences,” Dr. Nancy L. Pedersen from the Karolinska Institute, Stockholm, told Reuters Health. “Hence, further attempts to study risk factors in general for Parkinson’s disease should entertain the possibility that there are complex interactions between genetic mechanisms and putative risk factors.”

Pedersen and her colleagues investigated the previously reported link between smoking and a reduced risk for Parkinson’s by analyzing data from the Swedish Twin Registry.

The authors found that both current smokers and past smokers were less likely to develop Parkinson’s disease than people who had never smoked.

The association was stronger in men than in women and the risk of Parkinson’s decreased as the number of cigarettes smoked per week increased, the authors note in the Annals of Neurology.

As to the reason for the association, the researchers note that cigarette smoke may contains chemicals that protect nerve cells from damage.

Further analysis showed that neither alcohol nor coffee was associated with Parkinson’s disease risk.

“We have not planned any further studies directly, although we may be exploring whether there is a genetic interaction between smoking and certain genes,” Pedersen said.

SOURCE: Annals of Neurology, January 2005.