title: Smoking duration, intensity, and risk of Parkinson disease.
abstract: OBJECTIVE
  To evaluate the relative importance of smoking duration vs intensity in reducing the risk of Parkinson disease (PD).
  
  
  METHODS
  The study included 305,468 participants of the NIH-AARP Diet and Health cohort, of whom 1,662 had a PD diagnosis after 1995. We estimated odds ratios (OR) and 95% confidence intervals from multivariate logistic regression models.
  
  
  RESULTS
  Compared with never smokers, the multivariate ORs were 0.78 for past smokers and 0.56 for current smokers. Among past smokers, a monotonic trend toward lower PD risk was observed for all indicators of more smoking. Stratified analyses indicated that smoking duration was associated with lower PD risk within fixed intensities of smoking. For example, compared with never smokers, the ORs among past smokers who smoked >20 cigarettes/day were 0.96 for 1-9 years of smoking, 0.78 for 10-19 years, 0.64 for 20-29 years, and 0.59 for 30 years or more (p for trend = 0.001). In contrast, at fixed duration, the typical number of cigarettes smoked per day in general was not related to PD risk. Close examination of smoking behaviors in early life showed that patients with PD were less likely to be smokers at each age period, but if they smoked, they smoked similar numbers of cigarettes per day as individuals without PD.
  
  
  CONCLUSIONS
  This large study suggests that long-term smoking is more important than smoking intensity in the smoking-Parkinson disease relationship.
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences, 111 T.W. Alexander Dr., PO Box 12233, Mail drop A3-05, Research Triangle Park, NC 27709, USA. chenh2@niehs.nih.gov
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: X
authors.initials: X
authors.lastname: Huang
authors.forename: X
authors.initials: X
authors.lastname: Guo
authors.forename: R B
authors.initials: RB
authors.lastname: Mailman
authors.forename: Y
authors.initials: Y
authors.lastname: Park
authors.forename: F
authors.initials: F
authors.lastname: Kamel
authors.forename: D M
authors.initials: DM
authors.lastname: Umbach
authors.forename: Q
authors.initials: Q
authors.lastname: Xu
authors.forename: A
authors.initials: A
authors.lastname: Hollenbeck
authors.forename: A
authors.initials: A
authors.lastname: Schatzkin
authors.forename: A
authors.initials: A
authors.lastname: Blair
mesh_terms: D000367:Age Factors; D000368:Aged; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010300:Parkinson Disease / Q000453:epidemiology*; D012044:Regression Analysis; D012306:Risk; D012737:Sex Factors; D012907:Smoking / Q000453:epidemiology*; D016540:Smoking Cessation; D011795:Surveys and Questionnaires; D013997:Time Factors