title: The effects of smoking cessation on the risk of chronic obstructive pulmonary disease exacerbations.
abstract: BACKGROUND
  Smoking cessation has been demonstrated to reduce the rate of loss of lung function and mortality among patients with mild to moderate chronic obstructive pulmonary disease (COPD). There is a paucity of evidence about the effects of smoking cessation on the risk of COPD exacerbations.
  
  
  OBJECTIVE
  We sought to examine whether smoking status and the duration of abstinence from tobacco smoke is associated with a decreased risk of COPD exacerbations.
  
  
  METHODS
  We assessed current smoking status and duration of smoking abstinence by self-report. Our primary outcome was either an inpatient or outpatient COPD exacerbation. We used Cox regression to estimate the risk of COPD exacerbation associated with smoking status and duration of smoking cessation.
  
  
  METHODS
  We performed a cohort study of 23,971 veterans who were current and past smokers and had been seen in one of seven Department of Veterans Affairs (VA) primary care clinics throughout the US.
  
  
  RESULTS
  In comparison to current smokers, ex-smokers had a significantly reduced risk of COPD exacerbation after adjusting for age, comorbidity, markers of COPD severity and socio-economic status (adjusted HR 0.78, 95% CI 0.75-0.87). The magnitude of the reduced risk was dependent on the duration of smoking abstinence (adjusted HR: quit < 1 year, 1.04; 95% CI 0.87-1.26; 1-5 years 0.93, 95% CI 0.79-1.08; 5-10 years 0.84, 95% CI 0.70-1.00; > or = 10 years 0.65, 95% CI 0.58-0.74; linear trend <0.001).
  
  
  CONCLUSIONS
  Smoking cessation is associated with a reduced risk of COPD exacerbations, and the described reduction is dependent upon the duration of abstinence.
authors.affiliation: Health Services Research and Development, VA Puget Sound Health Care System, 1660 S. Columbian Way (152), Seattle, WA 98108, USA. dau@u.washington.edu
authors.forename: David H
authors.initials: DH
authors.lastname: Au
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Bryson
authors.forename: Jason W
authors.initials: JW
authors.lastname: Chien
authors.forename: Haili
authors.initials: H
authors.lastname: Sun
authors.forename: Edmunds M
authors.initials: EM
authors.lastname: Udris
authors.forename: Laura E
authors.initials: LE
authors.lastname: Evans
authors.forename: Katharine A
authors.initials: KA
authors.lastname: Bradley
mesh_terms: D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D016540:Smoking Cessation; D013997:Time Factors