Peppers, tobacco and other nicotine-carrying members of the plant family Solanaceae may reduce the risk of Parkinson's disease, according to a new publication in the Annals of Neurology.

"Our study is the first to investigate dietary nicotine and risk of developing Parkinson's disease," said lead author Dr. Susan Searles Nielsen, an epidemiologist at the University of Washington.

Parkinson's disease is a movement disorder that afflicts nearly 1 million people in the US, most over the age 50. It is caused by the gradual loss of dopamine-producing brain cells. The early stages are marked by hand tremors, speech changes, and rigidity, which can progress into cognitive plights like depression and dementia. There is no cure, but some drugs may markedly improve symptoms.

Multiple studies have hinted that smoking protects against Parkinson's disease. The Michael J. Fox Foundation cites estimations "that current smokers are 60 percent less likely to get Parkinson's disease than those who have never smoked". and recently launched a clinical trial in Germany and the US to test nicotine patches as a possible remedy.

Nicotine can interact with receptors in the brain, so there is a rationale for it to affect mental processes. However, physicians are unlikely to recommend cigarettes as a solution, given their negative impacts to health (lung cancer, hypertension, heart attack).

Tobacco belongs to a family of nicotine-containing plants called Solanaceae, which includes peppers, tomatoes, eggplant, and potatoes. Dr. Searles Nielsen wondered if any of these dietary sources of nicotine were also linked to a reduced risk of Parkinson's.

Her team surveyed 490 individuals with Parkinson's to assess their lifetime dietary habits, and these responses were compared to answers from 644 controls.

Of the Solanaceae plants recorded, her team found that peppers showed the best protection and reduce the relative risk of Parkinson's by more than 30% overall. The highest advantage was seen with people who ate over 2-4 peppers per week.

The 'pepper-Parkinson's connection' was somewhat surprising given that potatoes and tomatoes, given their popularity, are more substantial contributors of dietary nicotine. Cigarette smokers, moreover, received less benefit from pepper than smokers, suggesting there is more to this theory than just nicotine.

"Although this research came about because of the nicotine-Parkinson's hypothesis, it is possible that other compounds in these closely related plants are beneficial," said Dr. Searles. "It is worth pursuing whether this is the case."

But before you rush to clear out your grocery stores, Dr. Searles Nielsen cautions that further studies are needed to confirm the link.

One avenue could be to analyze the chemical compositions of both tobacco and peppers to see how else they overlap.

"If it is causal link, we want to figure out what is conferring that protection," she remarked. "Finding an answer will take the contribution of many studies and researchers, working together to chip away at that puzzle."