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Study Confirms Link to Lower Risk of Parkinson's

By Eddy Ball
April 2010

Honglei  Chen, M.D., Ph.D.
"Nobody would advocate smoking to prevent Parkinson's disease," said lead author Chen. "It's important to make that very, very clear."
(Photo courtesy of Steve McCaw)

Long-time smokers may suffer more preventable health problems than non-smokers, but their habit may also dramatically lower their risk of developing Parkinson's disease (PD), according to a new study led by NIEHS epidemiologist Honglei Chen, M.D., Ph.D.

Like other scientists who have studied the association of smoking with reduced risk for PD, authors of the study pointed out that the adverse health effects of smoking far outweigh any benefits of reduced risk for PD. Understanding the association is important, they maintain, "for determining the clinical usefulness of administering the active constituents of tobacco to new patients with PD and for guiding animal experimental research" into the underlying chemicals and biological mechanisms involved.

The study( Exit NIEHS, which appeared online March 10 in the journal Neurology, looked at detailed aspects of smoking over life in relation to PD in more than 300,000 participants of the NIH-AARP (American Association of Retired Persons) Diet and Health (DH) Study. This is the largest single study ever examined in this way, giving the study an unprecedented level of power to its support for the hypothesis that smoking may decrease PD risk.

The research team found that long-term and recent smoking were more important than intensity in conferring the protective effects of smoking. "The number of cigarettes smoked per day became irrelevant once adjusted for smoking duration or years since last smoking," the authors observed.

This bar graph from the study shows the dramatic decrease in  risk for PD associated with years of smoking.
This bar graph from the study shows the dramatic decrease in risk for PD associated with years of smoking. (Graph courtesy of Honglei Chen)

Compared to the reference group of never-smokers in the cohort, people who smoked for 30 years or longer had up to a 41 percent reduction in risk for PD. Participants who reported smoking for fewer than ten years showed a 4 to 15 percent reduction in risk.

The participants were among the more than 550,000 people 50-71 years old enrolled by the NIH-AARP DH study in 1995. They were followed up between 2004 and 2006 with a survey to update lifestyle exposure and occurrence of major chronic disease, including PD. In 2007, the research team began collecting saliva samples from surviving patients with PD for genetic research and validating PD diagnosis in the cohort in attempt to partially offset the limitations of self-reporting.

The study was supported by funding from NIEHS and the National Cancer Institute (NCI). In addition to Chen, the interdisciplinary team included NIEHS epidemiologists Freya Kamel, Ph.D., and Qun Xu, Ph.D., along with NIEHS biostatistician David Umbach, Ph.D.( Also on the team were researchers from NCI, Pennsylvania State University, and Westat Inc.

Citation: Chen H, Huang X, Guo X, Mailman RB, Park Y, Kamel F, et al( Exit NIEHS. 2010. Smoking duration, intensity, and risk of Parkinson disease. Neurology. Mar 10. [Epub ahead of print]

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