Environmental tobacco smoke and Parkinson's disease.

Background: Parkinson's disease is inversely associated with cigarette smoking, but its relation with passive smoking or environmental tobacco smoke exposure is rarely examined.

Methods: Within a case-control study, we assessed the association between Parkinson's disease and living or working with active smokers. Cases were newly diagnosed with idiopathic Parkinson's disease (n = 154) from western Washington State in 2002-2008. Age- and sex-matched controls (n = 173) were neurologically normal and unrelated to cases.

Results: Compared with never active or passive tobacco smokers, we observed reduced Parkinson's disease risks for ever passive only smokers (OR, 0.34; 95% CI, 0.16-0.73), similar to those for ever active smokers (OR, 0.35; 95% CI, 0.17-0.73). Among persons whose only tobacco smoke exposure was passive smoking at home, risk was inversely associated with years exposed.

Conclusions: These observations parallel those well established for active smoking. However, it remains unresolved whether a true protective effect of tobacco smoke, generally detrimental to health, underlies these associations.