title: Pooled analysis of tobacco use and risk of Parkinson disease.
abstract: BACKGROUND
  Epidemiologic studies have reported that cigarette smoking is inversely associated with Parkinson disease (PD). However, questions remain regarding the effect of age at smoking onset, time since quitting, and race/ethnicity that have not been addressed due to sample size constraints. This comprehensive assessment of the apparent reduced risk of PD associated with smoking may provide important leads for treatment and prevention.
  
  
  OBJECTIVE
  To determine whether race/ethnicity, sex, education, age at diagnosis, and type of tobacco modify the observed effects of smoking on PD.
  
  
  METHODS
  We conducted the first ever pooled analysis of PD combining individual-level data from 8 US case-control and 3 cohort studies (Nurses' Health Study, Health Professionals Follow-Up Study, and Honolulu-Asia Aging Study) conducted between 1960 and 2004. Case-control studies provided data for 2328 PD cases and 4113 controls matched by age, sex, and ethnicity; cohort studies contributed 488 cases and 4880 controls selected from age- and sex-matched risk sets.
  
  
  METHODS
  Incident PD.
  
  
  RESULTS
  We confirmed inverse associations between PD and smoking and found these to be generally stronger in current compared with former smokers; the associations were stronger in cohort than in case-control studies. We observed inverse trends with pack-years smoked at every age at onset except the very elderly (>75 years of age), and the reduction of risk lessened with years since quitting smoking. The risk reductions we observed for white and Asian patients were not seen in Hispanic and African American patients. We also found an inverse association both for smoking cigars and/or pipes and for chewing tobacco in male subjects.
  
  
  CONCLUSIONS
  Our data support a dose-dependent reduction of PD risk associated with cigarette smoking and potentially with other types of tobacco use. Importantly, effects seemed not to be influenced by sex or education. Differences observed by race and age at diagnosis warrant further study.
authors.affiliation: Department of Epidemiology and Environmental Health Sciences, UCLA School of Public Health, 650 Charles Young Smith Dr S, Los Angeles, CA 90095-1772, USA. britz@ucla.edu
authors.forename: Beate
authors.initials: B
authors.lastname: Ritz
authors.forename: Alberto
authors.initials: A
authors.lastname: Ascherio
authors.forename: Harvey
authors.initials: H
authors.lastname: Checkoway
authors.forename: Karen S
authors.initials: KS
authors.lastname: Marder
authors.forename: Lorene M
authors.initials: LM
authors.lastname: Nelson
authors.forename: Walter A
authors.initials: WA
authors.lastname: Rocca
authors.forename: G Webster
authors.initials: GW
authors.lastname: Ross
authors.forename: Daniel
authors.initials: D
authors.lastname: Strickland
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Van Den Eeden
authors.forename: Jay
authors.initials: J
authors.lastname: Gorell
mesh_terms: D017677:Age Distribution; D017668:Age of Onset; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D015897:Comorbidity; D004305:Dose-Response Relationship, Drug; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D015201:Meta-Analysis as Topic; D008875:Middle Aged; D016017:Odds Ratio; D010300:Parkinson Disease / Q000453:epidemiology* / Q000208:ethnology / Q000503:physiopathology; D044469:Racial Groups; D012307:Risk Factors; D017678:Sex Distribution; D016540:Smoking Cessation / Q000208:ethnology / Q000706:statistics & numerical data; D014029:Tobacco Use Disorder / Q000453:epidemiology* / Q000208:ethnology / Q000503:physiopathology