title: Smoking and colorectal cancer in a non-Western population: a prospective cohort study in Japan.
abstract: BACKGROUND
  The risk of colorectal cancer in relation to smoking habits has been examined mostly in Caucasians, and evidence for other ethnic groups is still scarce.
  
  
  METHODS
  Our data came from the Japan Collaborative Cohort (JACC) Study. From 1988 through 1990, 25,260 men and 34,619 women aged 40-79 years completed a questionnaire on cigarette smoking and other lifestyle factors. Hazard ratios (HR) were estimated by fitting proportional hazards models.
  
  
  RESULTS
  During the mean follow-up of 7.6 years through December 1997, we documented 408 incident colon cancers and 204 rectal cancers. We found a non-significant increase in colon cancer risk in male current smokers compared with never smokers. The multivariate-adjusted hazard ratios were 1.07 (95% confidence interval [CI]: 0.72-1.59) for ex-smokers and 1.23 (95% CI: 0.85-1.78) for current smokers. We however failed to observe a clear dose-response relationship between smoking intensity or duration and colon cancer risk. The adjusted hazard ratio was 1.07 (95% CI: 0.71-1.61) even for 40+ years of smoking. Almost no increase in colon cancer risk was detected for female smokers, and male smokers were not at an enhanced risk of rectal cancer.
  
  
  CONCLUSIONS
  Cigarette smoking was not a strong risk factor for colorectal cancer even after a long-term exposure, although a weak association remains open to discussion.
authors.affiliation: Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Nagoya 464-8681, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Wakai
authors.forename: Norihiko
authors.initials: N
authors.lastname: Hayakawa
authors.forename: Masayo
authors.initials: M
authors.lastname: Kojima
authors.forename: Koji
authors.initials: K
authors.lastname: Tamakoshi
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Koji
authors.initials: K
authors.lastname: Suzuki
authors.forename: Shuji
authors.initials: S
authors.lastname: Hashimoto
authors.forename: Shinkan
authors.initials: S
authors.lastname: Tokudome
authors.forename: Hideaki
authors.initials: H
authors.lastname: Toyoshima
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ito
authors.forename: Akiko
authors.initials: A
authors.lastname: Tamakoshi
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D044466:Asian People; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D015897:Comorbidity; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D017678:Sex Distribution; D012907:Smoking / Q000453:epidemiology*; D011795:Surveys and Questionnaires