Lower carotid intima media thickness is predicted by higher serum bilirubin in both non-diabetic and Type 2 diabetic subjects

Background: Higher serum bilirubin levels may be implicated cardiovascular protection. It is unknown whether the impact of serum bilirubin on carotid artery intima media thickness (IMT), a marker of subclinical atherosclerosis, is different in diabetic subjects compared to non-diabetic subjects. We assessed relationships of IMT with serum total bilirubin in non-diabetic and Type 2 diabetic subjects without clinically manifest cardiovascular disease.

Methods: IMT, total bilirubin, transaminases, C-reactive protein (CRP) and lipid levels were measured in 40 predominantly middle-aged non-diabetic and 80 diabetic subjects.

Results: IMT was higher in diabetic subjects compared to non-diabetic subjects (unadjusted, p<0.001), whereas bilirubin was not different (p=0.82). In both non-diabetic and in diabetic subjects, IMT was negatively related to bilirubin (β=-0.316, p=0.045 and β=-0.247 p=0.014, respectively) taking account of age, sex and mean arterial pressure. In the combined subjects, IMT remained independently related to bilirubin (β=-0.183, p=0.028) after additional adjustment for diabetes status, alcohol intake, transaminases, CRP and lipid levels. There was no interaction of bilirubin with the presence of diabetes on IMT (p=0.98).

Conclusion: Carotid artery IMT relates negatively to bilirubin in non-diabetic and Type 2 diabetic subjects. The association of subclinical atherosclerosis with bilirubin appears to be unaltered in the diabetic state.