title: Cigarette smoking and serum bilirubin subtypes in healthy Korean men: the Korea Medical Institute study.
abstract: OBJECTIVE
  Cigarette smoking is a modifiable risk factor for cardiovascular disease. Bilirubin is a potent antioxidant and its concentration decreases in smokers. However, studies about the association between cigarette smoking and bilirubin are scarce and most are limited to total bilirubin. Additionally, bilirubin is highly related to hemoglobin. Therefore, this study evaluates the association between bilirubin subtypes and cigarette smoking in healthy Korean men independently of hemoglobin.
  
  
  METHODS
  This study included 48 040 Korean men aged 30 to 87 years who visited the Korea Medical Institute for routine health examinations from January to December, 2007. The association of smoking with total, direct, and indirect bilirubin was assessed by logistic regression analysis taking into consideration differences in subjects and smoking characteristics.
  
  
  RESULTS
  Current smokers had lower bilirubin concentrations than never-smokers and ex-smokers. Smoking amount and duration were inversely significantly associated with total, direct, and indirect bilirubin. In a multivariable adjusted model, compared to never-smokers, the odds ratios (ORs) and 95% confidence intervals (CIs) of current smokers with the highest number of pack-years were 1.7 (1.6 to 1.9) for total, 1.5 (1.4 to 1.6) for direct, and 1.7 (1.6 to 1.9) for indirect bilirubin. After further adjustment for hemoglobin, this association became stronger (OR [95% CI], 2.1 [1.9 to 2.2] for total; 1.9 [1.8 to 2.0] for direct; 2.0 [1.9 to 2.2] for indirect bilirubin).
  
  
  CONCLUSIONS
  In this study, bilirubin subtypes are inversely associated with smoking status, smoking amount, and smoking duration in healthy Korean men independently of hemoglobin. Further studies are needed to investigate this association in healthy Korean women.
authors.affiliation: Institute for Health Promotion, Department of Epidemiology and Health Promotion, Yonsei University Graduate School of Public Health, Seoul, Korea.
authors.forename: Jaeseong
authors.initials: J
authors.lastname: Jo
authors.forename: Heejin
authors.initials: H
authors.lastname: Kimm
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Yun
authors.forename: Kyu Jang
authors.initials: KJ
authors.lastname: Lee
authors.forename: Sun Ha
authors.initials: SH
authors.lastname: Jee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001663:Bilirubin / Q000097:blood* / Q000145:classification; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D056910:Republic of Korea; D012907:Smoking / Q000097:blood*
chemical_list: D001663:Bilirubin