Published: May 9, 2013 | Updated: May 9, 2013

By Michael Smith , North American Correspondent, MedPage Today

Action Points

• Peppers, a nicotine-containing vegetable in the same family as tobacco, are associated with lower relative risk of Parkinson’s disease.
• Note that the effect was mainly noticeable among people who had never smoked, and other vegetables had no association with the neurological disease.

Image from MedPageToday.com

Peppers, a nicotine-containing vegetable in the same family as tobacco, are associated with a lower relative risk of Parkinson’s disease, researchers reported.

In a population-based case-control study, consumption of nicotine-containing vegetable — mainly peppers — was inversely associated with Parkinson’s, according to Susan Searles Nielsen, PhD, and colleagues at the University of Washington in Seattle.

The effect was mainly noticeable among people who had never smoked, and other vegetables had no association with the neurological disease, Searles Nielsen and colleagues reported online in Annals of Neurology.

The vegetables in question — red, green, and yellow peppers, tomatoes, and potatoes — are members of Solanaceae, a flowering plant family that includes tobacco. Several studies have suggested that smokers are less likely to develop Parkinson’s, perhaps because of a neuroprotective effect of nicotine.

To see if eating vegetables from theSolanaceae family might have a similar association, Searles Nielsen and colleagues looked at a cohort of 490 newly diagnosed Parkinson’s patients in Washington state, as well as 644 unrelated and neurologically normal controls.

They used a standard questionnaire to assess participants’ histories of vegetable consumption and tobacco and caffeine use.

Searles Nielsen and colleagues found that, overall, eating the nicotine-bearing plants was associated with a 19% reduction in the risk of Parkinson’s.

But the 95% confidence interval of the 0.81 relative risk ranged from 0.65 to 1.01 and the trend was non-significant atP=0.07.

However, the reduction in relative risk was larger and reached statistical significance among those who had never smoked, they found. Specifically:

• In the 241 cases and 239 controls who had never smoked, the relative risk was 0.69 with a 95% confidence interval from 0.47 to 1.00 and the trend was significant atP=0.05.
• In contrast, among the 245 cases and 397 controls who had been smokers, the relative risk was 0.89, with a 95% confidence interval from 0.68 to 1.17, which was not significant.

When the researchers repeated the analysis based on the amount of nicotine in each member of the Solanaceae family, they found that peppers led all the rest – although, again, the effect was not significant among smokers.

“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,” she said, “our findings also suggest a protective effect from nicotine, or perhaps a similar but less toxic chemical, in peppers and tobacco.”

The researchers cautioned that the amount of nicotine in vegetables is small compared with amounts obtained through either active or secondhand smoking. But, they noted, the biological effect of nicotine from tobacco is seen with relatively small amounts. They also noted that compounds other than nicotine might be responsible for the apparent effect.

Further study will be needed, they concluded, to “strengthen causal inferences” and perhaps eventually lead to dietary or pharmaceutical interventions.