title: Cigarette smoking and the risk of venous thromboembolism: the Tromsø Study.
abstract: BACKGROUND
  Conflicting findings have been reported on the association between smoking and the risk of venous thromboembolism (VTE).
  
  
  OBJECTIVE
  To conduct a prospective, population-based cohort study to investigate the association between cigarette smoking and the risk of incident VTE.
  
  
  METHODS
  Information on smoking habits was assessed by self-administered questionnaires in 24 576 subjects, aged 25-96 years, participating in the fourth Tromsø Study in 1994-1995. Incident cases of VTE were registered until the end of follow-up at 1 September 2007.
  
  
  RESULTS
  A total of 389 incident VTE events (1.61 per 1000 person-years) were registered during follow-up (median of 12.5 years). Heavy smokers (> 20 pack-years) had a hazard ratio (HR) of 1.46 (95% confidence interval [CI] 1.04-2.05) for total VTE, and and an HR of 1.75 (95% CI 1.14-2.69) for provoked VTE, as compared with never smokers. The risk of provoked VTE increased with more pack-years of smoking (P = 0.02). Smoking was not associated with risk of unprovoked VTE. The number of pack-years was associated with increased risk of cancer and myocardial infarction, whereas the association between pack-years of smoking and VTE disappeared when failure times were censored at the occurrence of cancer or myocardial infarction.
  
  
  CONCLUSIONS
  Heavy smoking was apparently a risk factor for provoked VTE in analyses with VTE events as the only outcome. The lack of association between smoking and risk of VTE in analyses censored at the occurrence of cancer or myocardial infarction may suggest that smoking-attributable diseases or other predisposing factors are essential for smoking to convey a risk of VTE.
authors.affiliation: Hematological Research Group (HERG), Department of Clinical Medicine, University of Tromsø, Norway. kristin.f.enga@uit.no
authors.forename: K F
authors.initials: KF
authors.lastname: Enga
authors.forename: S K
authors.initials: SK
authors.lastname: Braekkan
authors.forename: I J
authors.initials: IJ
authors.lastname: Hansen-Krone
authors.forename: S
authors.initials: S
authors.lastname: le Cessie
authors.forename: F R
authors.initials: FR
authors.lastname: Rosendaal
authors.forename: J-B
authors.initials: JB
authors.lastname: Hansen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006184:Habits; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009203:Myocardial Infarction / Q000453:epidemiology; D009369:Neoplasms / Q000453:epidemiology; D009664:Norway / Q000453:epidemiology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D054556:Venous Thromboembolism / Q000453:epidemiology*