title: Effects of smoking and antioxidant micronutrients on risk of colorectal cancer.
abstract: OBJECTIVE
  Antioxidant intake has been reported to increase the risk of colorectal cancer (CRC) for smokers, yet reduce the risk for nonsmokers. We investigated the association between tobacco smoking and risk of colon or rectal cancer, and whether dietary and supplemental intake of the antioxidant vitamins A, C, E, β-carotene, selenium, zinc, and manganese affects the risk of CRC among smokers.
  
  
  METHODS
  Data on smoking habits and antioxidant intake were analyzed for 54,208 participants in the Danish Prospective Diet, Cancer and Health Study. Of these participants, 642 were diagnosed with colon cancer and 348 were diagnosed with rectal cancer. Hazard ratios and 95% confidence intervals were estimated using Cox proportional hazard models. Principal components were used to analyze intake of combinations of antioxidants.
  
  
  RESULTS
  Ever smoking increased the risk for CRC (hazard ratio, 1.19; 95% confidence interval, 1.03-1.37), especially for rectal cancer. Smoking for at least 20 years was associated with a 26% increase in risk of CRC, compared with never smokers, and smoking 20 g tobacco or more each day was associated with a 30% increase in risk. Smoking for more than 30 years, or more than 20 g tobacco each day, was associated with a 48% increase in risk of rectal cancer. We did not observe an interaction between smoking and antioxidant consumption on risk of CRC.
  
  
  CONCLUSIONS
  Tobacco smoking increases the risk for CRC. We did not observe that consumption of antioxidant micronutrients modulates the effects of smoking on CRC risk.
authors.affiliation: Danish Cancer Society Research Center, Copenhagen, Denmark. rikkehan@cancer.dk
authors.forename: Rikke Dalgaard
authors.initials: RD
authors.lastname: Hansen
authors.forename: Vanna
authors.initials: V
authors.lastname: Albieri
authors.forename: Anne
authors.initials: A
authors.lastname: Tjønneland
authors.forename: Kim
authors.initials: K
authors.lastname: Overvad
authors.forename: Klaus Kaae
authors.initials: KK
authors.lastname: Andersen
authors.forename: Ole
authors.initials: O
authors.lastname: Raaschou-Nielsen
mesh_terms: D000368:Aged; D000975:Antioxidants / Q000009:adverse effects*; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D003718:Denmark / Q000453:epidemiology; D004032:Diet / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018977:Micronutrients / Q000009:adverse effects*; D008875:Middle Aged; D018570:Risk Assessment; D012907:Smoking / Q000009:adverse effects*
chemical_list: D000975:Antioxidants; D018977:Micronutrients