Association between cigarette smoking and Parkinson's disease: A meta-analysis.
OBJECTIVE
To evaluate the association of Parkinson's disease (PD) with smoking, and determine whether gender, source of controls, dose of smoking, and year of studies modify the observed effects of smoking on PD.


METHODS
Available publications between 1959 and 2014 from PubMed, ScienceDirect, Springer Link and Web of Science databases were searched and carefully selected. Relative risks RR of specific study were weighted to obtain a pooled RR estimate and its 95% confidence interval CI.


RESULTS
61 case-control and 8 cohort studies were included. The pooled RR of PD was 0.59 (95% CI, 0.56-0.62) for ever smokers compared with never smokers. The stratified analyses indicated a somewhat greater impact of smoking on PD risk in cohort studies than in case-control studies, the protective effect was relatively significant in men more than in women and the inverse effect was slightly greater in hospital-based studies than in population-based studies. Furthermore, a significant inverse dose-response relationship was observed for the number of pack-years smoked. The summary RR for those smoking more than 30 pack-years was 0.66 (95% CI, 0.49-0.88), and 0.39 (95% CI, 0.29-0.53) for those smoking less than 30 pack-years.


CONCLUSIONS
The results demonstrated the inverse association between cigarette smoking and the risk of PD. We suggest that effective drugs for PD might be developed using chemical substances derived from tobacco or tobacco smoke.
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China; Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China.
Xiao
X
Li
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.
Weihua
W
Li
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.
Guixia
G
Liu
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China.
Xu
X
Shen
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China. Electronic address: ytang234@ecust.edu.cn.
Yun
Y
Tang
D000328:Adult; D005260:Female; D006761:Hospitals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009538:Nicotine / Q000008:administration & dosage*; D010300:Parkinson Disease / Q000453:epidemiology*; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology
D009538:Nicotine
Cigarette smoking; Meta-analysis; Pack-year; Parkinson’s disease