A meta‐analysis of coffee drinking, cigarette smoking, and the risk of Parkinson's disease

We conducted a systematic review to summarize the epidemiological evidence on the association between cigarette smoking, coffee drinking, and the risk of Parkinson's disease. Case-control and cohort studies that reported the relative risk of physician-confirmed Parkinson's disease by cigarette smoking or coffee drinking status were included. Study-specific log relative risks were weighted by the inverse of their variances to obtain a pooled relative risk and its 95% confidence interval (CI). Results for smoking were based on 44 case-control and 4 cohort studies, and for coffee 8 case-control and 5 cohort studies. Compared with never smokers, the relative risk of Parkinson's disease was 0.59 (95% CI, 0.54-0.63)…