title: Leanness and lung cancer risk: fact or artifact?
abstract: BACKGROUND
  More than a dozen studies have examined the association between leanness and increased lung cancer risk. None of the prospective studies has been large enough to allow exclusion of smokers or persons with preexisting disease, two factors that cause both leanness and poor survival and thus may cause a spurious association between low body mass index and fatal lung cancer.
  
  
  METHODS
  Using Cox proportional hazards models, we examined this issue in a cohort of 941,105 U.S. adults enrolled in an American Cancer Society prospective study in 1982. During 14 years of follow-up, 14,066 people died of lung cancer.
  
  
  RESULTS
  In analyses restricted to lifelong nonsmokers who did not report preexisting disease, leanness was not substantially associated with lung cancer mortality in men (rate ratio = 0.9; 95% confidence interval = 0.3-3.1) or in women (rate ratio = 1.2; 95% confidence interval = 0.7-2.1). However, leanness was associated with increased lung cancer risk in analyses that attempted to control for, rather than exclude, smokers and persons with preexisting disease.
  
  
  CONCLUSIONS
  These data suggest that the association between leanness and lung cancer mortality is not causal but rather is an artifact of the effects of smoking and preexisting disease.
authors.affiliation: Epidemiology and Surveillance Research, American Cancer Society, Atlanta, GA 30329, USA. jane.henley@cancer.org
authors.forename: S Jane
authors.initials: SJ
authors.lastname: Henley
authors.forename: W Dana
authors.initials: WD
authors.lastname: Flanders
authors.forename: Amita
authors.initials: A
authors.lastname: Manatunga
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Thun
mesh_terms: D000328:Adult; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000150:complications* / Q000453:epidemiology* / Q000503:physiopathology; D008297:Male; D016016:Proportional Hazards Models; D044469:Racial Groups; D012907:Smoking / Q000453:epidemiology; D011795:Surveys and Questionnaires; D013851:Thinness / Q000150:complications*; D014481:United States / Q000453:epidemiology