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

Abstract

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) for ever smokers, 0.80 (95% CI, 0.69-0.93) for past smokers, and 0.39 (95% CI, 0.32-0.47) for current smokers. The relative risk per 10 additional pack-years was 0.84 (95% CI, 0.81-0.88) in case-control studies and 0.78 (95% CI, 0.73-0.84) in cohort studies. Compared with non-coffee drinkers, relative risk of Parkinson's disease was 0.69 (95% CI, 0.59-0.80) for coffee drinkers. The relative risk per three additional cups of coffee per day was 0.75 (95% CI, 0.64-0.86) in case-control studies and 0.68 (95% CI, 0.46-1.00) in cohort studies. This meta-analysis shows that there is strong epidemiological evidence that smokers and coffee drinkers have a lower risk of Parkinson's disease. Further research is required on the biological mechanisms underlying this potentially protective effect.

Epidemiology and etiology of Parkinson’s disease: a review of the evidence

“…In an earlier meta-analysis that included 46 studies (with high degree of overlap with the Hernan study [436]) the summary estimate was 0.57 (95% CI 0.52-0.63) for ever versus never smokers [437].…”

“…A meta-analysis including 44 case-control and four cohort studies reported a pooled RR of 0.59 (95% CI 0.54-0.63) for ever versus never smokers, 0.39 (95% CI 0.32-0.47) for current versus never smokers, and 0.80 (95% CI 0.69-0.83) for past versus never smokers [436]. In an earlier meta-analysis that included 46 studies (with high degree of overlap with the Hernan study [436]) the summary estimate was 0.57 (95% CI 0.52-0.63) for ever versus never smokers [437].…”

“…Hernan et al [436] noted that the inverse association between smoking and PD was stronger in cohort studies than in case-control studies, especially for the comparison of past versus never smokers. Further, these authors found low heterogeneity between studies and no evidence for publication bias.…”

“…The authors concluded that the epidemiologic evidence of an inverse association between coffee drinking and PD is strong and that confounding is unlikely, although reverse causation cannot be completely ruled out [436].…”

Cost‐effectiveness of increasing the reach of smoking cessation interventions in Germany: results from the EQUIPTMOD

“…For missing inputs, Cochrane effectiveness inputs from a wide range of studies world‐wide were used, and represented rigorous and well‐accepted evidence. Some reported but controversial protective effects of smoking, such as those regarding Parkinson disease 63, 64, 65, 66, 67, 68, 69, 70, 71, were not accounted for in this model. Some diseases attributable to smoking 5 were also not included in the model, as the true impact of smoking could not be estimated, and some interventions available only in the United Kingdom but not in Germany were also not considered.…”