title: Parkinson disease and smoking revisited: ease of quitting is an early sign of the disease.
abstract: OBJECTIVE
  To assess whether being able to quit smoking is an early marker of Parkinson disease (PD) onset rather than tobacco being "neuroprotective," we analyzed information about ease of quitting and nicotine substitute use.
  
  
  METHODS
  For this case-control study, we identified 1,808 patients with PD diagnosed between 1996 and 2009 from Danish registries, matched 1,876 population controls on sex and year of birth, and collected lifestyle information. We estimated odds ratios and 95% confidence intervals with logistic regression adjusting for matching factors and confounders.
  
  
  RESULTS
  Fewer patients with PD than controls ever established a smoking habit. Among former smokers, those with greater difficulty quitting or using nicotine substitutes were less likely to develop PD, with the risk being lowest among those reporting "extremely difficult to quit" compared with "easy to quit." Nicotine substitute usage was strongly associated with quitting difficulty and duration of smoking, i.e., most strongly among current smokers, followed by former smokers who had used nicotine substitutes, and less strongly among former smokers who never used substitutes.
  
  
  CONCLUSIONS
  Our data support the notion that patients with PD are able to quit smoking more easily than controls. These findings are compatible with a decreased responsiveness to nicotine during the prodromal phase of PD. We propose that ease of smoking cessation is an aspect of premanifest PD similar to olfactory dysfunction, REM sleep disorders, or constipation and suggests that the apparent "neuroprotective" effect of smoking observed in epidemiologic studies is due to reverse causation.
authors.affiliation: From the Department of Epidemiology (B.R., O.A.A.), University of California at Los Angeles School of Public Health; Department of Neurology (B.R.), School of Medicine, University of California at Los Angeles; Department of Health Care Management (P.-C.L.), College of Healthcare Administration and Management, National Taipei University of Nursing Health Sciences, Taiwan; and Danish Cancer Society Research Center (C.F.L.), Danish Cancer Society, Copenhagen, Denmark. britz@ucla.edu.
authors.forename: Beate
authors.initials: B
authors.lastname: Ritz
authors.affiliation: From the Department of Epidemiology (B.R., O.A.A.), University of California at Los Angeles School of Public Health; Department of Neurology (B.R.), School of Medicine, University of California at Los Angeles; Department of Health Care Management (P.-C.L.), College of Healthcare Administration and Management, National Taipei University of Nursing Health Sciences, Taiwan; and Danish Cancer Society Research Center (C.F.L.), Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Pei-Chen
authors.initials: PC
authors.lastname: Lee
authors.affiliation: From the Department of Epidemiology (B.R., O.A.A.), University of California at Los Angeles School of Public Health; Department of Neurology (B.R.), School of Medicine, University of California at Los Angeles; Department of Health Care Management (P.-C.L.), College of Healthcare Administration and Management, National Taipei University of Nursing Health Sciences, Taiwan; and Danish Cancer Society Research Center (C.F.L.), Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Christina F
authors.initials: CF
authors.lastname: Lassen
authors.affiliation: From the Department of Epidemiology (B.R., O.A.A.), University of California at Los Angeles School of Public Health; Department of Neurology (B.R.), School of Medicine, University of California at Los Angeles; Department of Health Care Management (P.-C.L.), College of Healthcare Administration and Management, National Taipei University of Nursing Health Sciences, Taiwan; and Danish Cancer Society Research Center (C.F.L.), Danish Cancer Society, Copenhagen, Denmark.
authors.forename: Onyebuchi A
authors.initials: OA
authors.lastname: Arah
mesh_terms: D016022:Case-Control Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010300:Parkinson Disease / Q000175:diagnosis* / Q000453:epidemiology; D012042:Registries; D012306:Risk; D012907:Smoking / Q000453:epidemiology / Q000628:therapy; D016540:Smoking Cessation / Q000379:methods / Q000523:psychology*; D061485:Tobacco Use Cessation Devices