Tobacco, coffee, and Parkinson's disease

Parkinson's disease belongs to that small group of conditions that occur less often among cigarette smokers than in non-smokers. The observation was first made in a case-control study over 30 years ago,1 but, as Hernan and colleagues have shown in their recent systematic review and meta-analysis,2 the finding has been replicated many times. The protective effect is large—according to the pooled data, current smokers have a 60% reduction in risk compared with those who have never smoked—and consistent between studies in different settings. The fact that two very large prospective studies found a similar reduction in risk to that seen in retrospective studies rules out the possibility that the association can be accounted for by differential survival between smokers and non-smokers.3 Coffee drinking too, seems to protect against Parkinson's disease. Here the pooled estimate is a 30% reduction in risk for coffee drinkers compared with non-drinkers.