Smoking and Parkinson’s disease

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Abstract
Objective: To determine whether an inverse dose–response relationship exists between cigarette smoking and PD among ever-smokers and ex-smokers. Methods: Smoking and alcohol consumption were analyzed in 144 PD patients and 464 control subjects, who were frequency matched for sex, race, and age (±5 years), in a population-based case-control study of men and women ≥50 years old in the Henry Ford Health System. Results: With never-smokers as the reference category, there was an inverse association between current light smokers (>0 to 30 pack-years) and PD patients (odds ratio [OR], 0.59; 95% CI, 0.23 to 1.53), and a stronger inverse association of PD with current heavy smokers (>30 pack-years; OR, 0.08; 95% CI, 0.01 to 0.62). When former >30–pack-year smokers were stratified by the interval since quitting, there was an inverse association between those who stopped >20 years ago and PD (OR, 0.86; 95% CI, 0.42 to 1.75), and a greater inverse relationship with those who stopped 1 to 20 years ago (OR, 0.37; 95% CI, 0.19 to 0.72). Alcohol consumption had no independent, significant association with PD, but heavy drinking (>10 drink-years) had a greater effect than light–moderate drinking in reducing but not eliminating the inverse association between smoking and PD. Conclusions: The inverse dose–response relationship between PD and smoking and its cessation is unlikely to be due to bias or confounding, as discussed, providing indirect evidence that smoking is biologically protective.