title: Second hand smoke, age of exposure and lung cancer risk.
abstract: BACKGROUND
  Exposure to second hand smoke (SHS) has been identified as a risk factor for lung cancer for three decades. It is also known that the lung continues to grow from birth to adulthood, when lung growth stops. We hypothesize that after adjusting for active cigarette smoking, if SHS exposure took place during the period of growth, i.e. in the earlier part of life (0-25 years of age) the risk of lung cancer is greater compared to an exposure occurring after age 25.
  
  
  METHODS
  Second hand smoke exposure was self-reported for three different activities (leisure, work and at home) for this study population of 1669 cases and 1263 controls. We created variables that captured location of exposure and timing of first exposure with respect to a study participant's age (0-25, >25 years of age). Multiple logistic regressions were used to study the association between SHS exposure and lung cancer, adjusting for age, gender and active smoking variables.
  
  
  RESULTS
  For study participants that were exposed to SHS at both activities (work and leisure) and compared to one or no activity, the adjusted odds ratio (AOR) for lung cancer was 1.30 (1.08-1.57) when exposure occurred between birth and age 25 and 0.66 (0.21-1.57) if exposure occurred after age 25 years. Respective results for non-smokers were 1.29 (0.82-2.02) and 0.87 (0.22-3.38), and current and ex-smokers combined 1.28 (1.04-1.58) and 0.66 (0.15-2.85).
  
  
  CONCLUSIONS
  All individuals exposed to SHS have a higher risk of lung cancer. Furthermore, this study suggests that subjects first exposed before age 25 have a higher lung cancer risk compared to those for whom first exposure occurred after age 25 years.
authors.affiliation: Department of Environmental Heath (Environmental and Occupational Medicine and Epidemiology Program), Harvard School of Public Health, Boston, MA 02115, United States.
authors.forename: Kofi
authors.initials: K
authors.lastname: Asomaning
authors.forename: David P
authors.initials: DP
authors.lastname: Miller
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Liu
authors.forename: John C
authors.initials: JC
authors.lastname: Wain
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Lynch
authors.forename: Li
authors.initials: L
authors.lastname: Su
authors.forename: David C
authors.initials: DC
authors.lastname: Christiani
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008168:Lung / Q000254:growth & development; D008175:Lung Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D008297:Male; D012307:Risk Factors; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution