title: The effect of occasional smoking on smoking-related cancers: in the European Prospective Investigation into Cancer and Nutrition (EPIC).
abstract: OBJECTIVE
  Most studies on tobacco smoking have focused on daily-smokers. Occasional smokers, who have never smoked daily, have often been included in the reference group of never-smokers. We have investigated the association between occasional smoking and cancer of the bladder, kidney, pancreas, upper aero-digestive tract and lung.
  
  
  METHODS
  The study population consisted of 158,488 persons, who provided information on occasional smoking, within the European Prospective Investigation into Cancer and Nutrition (EPIC), 780 of whom developed a smoking-related cancer. We used Cox proportional hazard model, stratified by gender and country to estimate incidence rate ratios (IRR) for smoking-related cancers.
  
  
  RESULTS
  The results suggest that occasional smokers have a higher risk of bladder cancer (IRR: 1.92, 95% confidence interval (CI) 0.93-3.98) and of the major smoking-related cancers combined (IRR: 1.24, 95% CI 0.80-1.94) than true never-smokers. Including occasional smokers in the reference group resulted in a lower risk estimate for former and current smokers.
  
  
  CONCLUSIONS
  Occasional smoking should be discouraged.
authors.affiliation: Institute of Cancer Epidemiology, Danish Cancer Society, Strandboulevarden 49, 2100, Copenhagen Ø, Denmark.
authors.forename: Bine Kjøller
authors.initials: BK
authors.lastname: Bjerregaard
authors.forename: Ole
authors.initials: O
authors.lastname: Raaschou-Nielsen
authors.forename: Mette
authors.initials: M
authors.lastname: Sørensen
authors.forename: Kirsten
authors.initials: K
authors.lastname: Frederiksen
authors.forename: Anne
authors.initials: A
authors.lastname: Tjønneland
authors.forename: Sabine
authors.initials: S
authors.lastname: Rohrmann
authors.forename: Jakob
authors.initials: J
authors.lastname: Linseisen
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Bergman
authors.forename: Heiner
authors.initials: H
authors.lastname: Boeing
authors.forename: Sabina
authors.initials: S
authors.lastname: Sieri
authors.forename: Domenico
authors.initials: D
authors.lastname: Palli
authors.forename: Rosario
authors.initials: R
authors.lastname: Tumino
authors.forename: Carlotta
authors.initials: C
authors.lastname: Sacerdote
authors.forename: H Bas
authors.initials: HB
authors.lastname: Bueno-de-Mesquita
authors.forename: Frederike L
authors.initials: FL
authors.lastname: Büchner
authors.forename: Inger Torhild
authors.initials: IT
authors.lastname: Gram
authors.forename: Tonje
authors.initials: T
authors.lastname: Braaten
authors.forename: Eiliv
authors.initials: E
authors.lastname: Lund
authors.forename: Göran
authors.initials: G
authors.lastname: Hallmans
authors.forename: Asa
authors.initials: A
authors.lastname: Agren
authors.forename: Elio
authors.initials: E
authors.lastname: Riboli
mesh_terms: D000328:Adult; D000368:Aged; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology*; D009749:Nutrition Surveys; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*