Increased duration of diabetes is associated with lower serum bilirubin concentration in type 2 diabetic patients

Objective To investigate the association between physiological serum bilirubin concentration and duration of type 2 diabetes. Methods A total of 1 272 patients with type 2 diabetes admitted to the Department of Endocrinology of Ningbo First Hospital from January 2013 to June 2015 were included for the study. Clinic parameters were collected from electronic medical records. All subjects were classified into four groups by diabetes duration quartiles (<5 years, 5-9 years, 10-14 years and ≥15 years). The adjusted concentration of three types of bilirubin were calculated and compared using covariance analysis. Pearson correlation analysis and multiple linear regression analysis were adopted to examine the relationship between duration of diabetes and serum bilirubin. Results With increase of diabetes duration from the lowest quartiles to the highest quartiles, serum total bilirubin, direct bilirubin and indirect bilirubin concentration tended to decrease. This trend persisted after adjustment for age, gender, hemoglobin, smoking, drinking, blood pressure, lipid profile, weight, ALT, AST, HbA1c and statin use. The adjusted mean concentration of total bilirubin from the lowest quartiles to the highest quartiles for diabetes duration was 13.26, 12.36, 12.07 and 11.71 μmol/L (F=4.36, P=0.005). The direct bilirubin was 5.01, 4.67, 4.47 and 4.35 μmol/L (F=4.63, P=0.003).The indirect bilirubin was 8.25, 7.69, 7.60 and 7.37 μmol/L (F=2.96, P=0.033). Pearson correlation analysis showed that total bilirubin concentration (r=-0.241, P<0.01), direct bilirubin concentration (r=-0.23, P<0.01), and indirect bilirubin concentration (r=-0.21, P<0.01) were inversely correlated with duration of diabetes. Multiple linear regression analysis showed that an increment of one year in diabetes duration was associated with 0.087 mmol/L decrease in total bilirubin, 0.037 mmol/L in direct bilirubin and 0.051 mmol/L in indirect bilirubin separately. Conclusion Serum bilirubin concentration is negatively correlated with duration of type 2 diabetes mellitus in Chinese patients. Key words: Diabetes mellitus, type 2; Bilirubin; Duration