Direct bilirubin is associated with low-density lipoprotein subfractions and particle size in overweight and centrally obese women.

BACKGROUND AND AIMS: Bilirubin has antioxidant and anti-inflammatory properties; serum bilirubin levels have been known to be inversely associated with cardiovascular disease. However, the effects of different bilirubin subtypes on cardiometabolic traits are unknown. In this study, we aimed to determine whether direct bilirubin is more strongly correlated with small, dense low-density lipoprotein (sdLDL) compared to other bilirubin subtypes. We also investigated which LDL subfractions exhibited the highest correlation with direct bilirubin.

METHODS AND RESULTS: A total of 288 overweight and centrally obese women were included in this study. The Pearson correlation and Steiger's Z test were used to compare the correlation coefficients between bilirubin subtypes and lipoproteins. Multiple linear regression analyses were used to evaluate the independent association between direct bilirubin and mean LDL particle size. Only direct bilirubin levels were significantly associated with the sdLDL subfraction and mean LDL particle size. Mean LDL particle size exhibited a significantly stronger correlation with direct bilirubin than sdLDL, percent sdLDL, and the sdLDL:large LDL ratio. Regression analysis showed that direct bilirubin was significantly associated with mean LDL particle size, according to both the stepwise method (β = 11.445, P value = 0.002) and the enter method (β = 11.655, P value = 0.002).

CONCLUSIONS: Direct bilirubin is more strongly correlated with the sdLDL subfraction compared with total and indirect bilirubin, and is independently associated with mean LDL particle size in overweight and centrally obese women.