Abstract
Objective: Bilirubin has strong antioxidative activity and thus may have a protective effect against the progression of atherosclerosis. We recently reported a significant correlation between serum levels of total bilirubin and smoking or obesity, As few studies have separately examined such correlations with direct or indirect bilirubin, in the present study we evaluated correlations between them and smoking.
Methods: Our subjects were 8,955 men (average age 48.1±10.1 years old) who underwent an annual heath check-up at our clinic in 2010 and had serum total bilirubin levels under 2.3mg/dl. A self-administered health questionnaire about smoking was used. Correlations among blood pressure, liver function, blood sugar, serum lipid levels and smoking were analyzed as dependent variables in logistic regression models.
Results: The questionnaire revealed that there were 2,570 smokers (28.7%). Both serum levels of direct and indirect bilirubin in non-smokers were significantly higher than those in smokers. Significantly positive correlations between direct bilirubin and AST, ALT or γ-GTP were observed, although correlation coefficients were not high. On the other hand, there were negative correlations between indirect bilirubin and ALT or γ-GTP. Logistic regression analyses showed that there was a significant correlation between smoking and indirect bilirubin (odds ratio; 0.243), but not between smoking and direct bilirubin.
Conclusions: The present study revealed a significant correlation between smoking and indirect bilirubin. This finding suggests that serum levels of indirect bilirubin may be a smoking indicator.
