• Fei Yang, Nancy L Pedersen, Weimin Ye, Zhiwei Liu, Margareta Norberg, Lars Forsgren, Ylva Trolle Lagerros, Rino Bellocco, Lars Alfredsson, Anders Knutsson, Jan-Håkan Jansson, Patrik Wennberg, Maria Rosaria Galanti, Anton C J Lager, Marzieh Araghi, Michael Lundberg, Cecilia Magnusson, and Karin Wirdefeldt.
• Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
• Int J Epidemiol. 2017 Jun 1; 46 (3): 872-880.

BackgroundCigarette smoking is associated with a lower risk of Parkinson's disease. It is unclear what constituent of tobacco smoke may lower the risk. Use of Swedish moist smokeless tobacco (snus) can serve as a model to disentangle what constituent of tobacco smoke may lower the risk. The aim of this study was to determine whether snus use was associated with a lower risk of Parkinson's disease.MethodsIndividual participant data were collected from seven prospective cohort studies, including 348 601 men. We used survival analysis with multivariable Cox regression to estimate study-specific relative risk of Parkinson's disease due to snus use, and random-effects models to pool estimates in a meta-analysis. The primary analyses were restricted to never-smokers to eliminate the potential confounding effect of tobacco smoking.ResultsDuring a mean follow-up time of 16.1 years, 1199 incident Parkinson's disease cases were identified. Among men who never smoked, ever-snus users had about 60% lower Parkinson's disease risk compared with never-snus users [pooled hazard ratio (HR) 0.41, 95% confidence interval (CI) 0.28-0.61]. The inverse association between snus use and Parkinson's disease risk was more pronounced in current (pooled HR 0.38, 95% CI 0.23-0.63), moderate-heavy amount (pooled HR 0.41, 95% CI 0.19-0.90) and long-term snus users (pooled HR 0.44, 95% CI 0.24-0.83).ConclusionsNon-smoking men who used snus had a substantially lower risk of Parkinson's disease. Results also indicated an inverse dose-response relationship between snus use and Parkinson's disease risk. Our findings suggest that nicotine or other components of tobacco leaves may influence the development of Parkinson's disease.© The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association

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