Dr. Susan Searles Nielsen and colleagues at the University of Washington in Seattle recruited 490 patients newly diagnosed with Parkinson's disease at the university's Neurology Clinic or a regional health maintenance organization, Group Health Cooperative. Another 644 unrelated individuals without neurological conditions were used as controls.
The study participants completed questionnaires on diet and tobacco use, which researchers defined as ever having smoked more than 100 cigarettes or regularly using cigars, pipes or smokeless tobacco.
Vegetable consumption in general did not affect Parkinson's disease risk, but as consumption of edible Solanaceae -- a flowering plant family with some species producing foods that are edible sources of nicotine -- increased, the risk of Parkinson's decreased. Peppers displayed the strongest association, the researchers found.
The researchers noted the apparent protection from Parkinson's occurred mainly in men and women with little or no prior use of tobacco, which contains much more nicotine than the foods studied.
"Our study is the first to investigate dietary nicotine and risk of developing Parkinson's disease," Searles Nielsen said in a statement. "Similar to the many studies that indicate tobacco use might reduce risk of Parkinson's, our findings also suggest a protective effect from nicotine, or perhaps a similar but less toxic chemical in peppers and tobacco."
The study was published in the Annals of Neurology.