Population-based case-control study of cigarette smoking and essential tremor.

Parkinson's disease (PD) is inversely associated with smoking cigarettes. Despite long-standing clinical links between PD and essential tremor (ET), there are surprisingly few data on smoking in ET. We studied whether smoking cigarettes is inversely associated with ET. Using a population-based, case-control design, cigarette smoking habits were assessed in 221 prevalent ET cases (75.5 +/- 7.1 years old) and 663 matched controls (74.6 +/- 7.0 years old). In logistical regression analyses, diagnosis (ET vs. control) was the dependent variable, and cigarette smoking status, the independent variable. Ever smokers were marginally less likely to have ET than were never smokers (22.0% vs. 27.0%, odds ratio [OR] 0.76, 95% confidence interval [CI] 0.55-1.04, P = 0.09). In an analysis that adjusted for confounding factors (drink-years and depressive symptoms), ever smokers were nearly half less likely to have ET than the never smokers (OR 0.58, 95% CI 0.40-0.84, P = 0.004). There was a strong inverse association between pack-years and odds of ET (adjusted OR 0.991, 95% CI 0.984-0.997, P = 0.005, i.e., with every 10 pack-year increase, odds of ET were lowered 10%). Ever smokers in the highest pack-year tertile were one-third as likely to have ET than the never smokers (adjusted OR 0.39, 95% CI 0.22-0.69, P = 0.001). We demonstrated an inverse association between ever smoking and ET. Additional studies are needed to reproduce these findings and assess whether this association is due to a biologically protective effect.