Mildly elevated serum total bilirubin is negatively associated with hemoglobin A1c independently of confounding factors among community-dwelling middle-aged and elderly persons

Abnormally high glycated hemoglobin (Hb) (HbA1c) is significantly associated with oxidative stress and an increased risk of cardiovascular disease (CVD). Serum total bilirubin (T-B) may have a beneficial role in preventing oxidative changes and be a negative risk factor of CVD. Limited information is available on whether serum T-B is an independent confounding factor of HbA1c. The study subjects were 633 men aged 70 ± 9 (mean ± standard deviation (SD)) years and 878 women aged 70 ± 8 years who were enrolled consecutively from among patients aged ≥40 years through a community-based annual check-up process. We evaluated the relationship between various confounding factors including serum T-B and HbA1c in each gender. Multiple linear regression analysis pertaining to HbA1c showed that in men, serum T-B (β = -0.139) as well as waist circumference (β = 0.099), exercise habit (β = 0.137), systolic blood pressure (SBP) (β = 0.076), triglycerides (β = 0.087), and uric acid (β = -0.123) were significantly and independently associated with HbA1c, and in women, serum T-B (β = -0.084) as well as body mass index (β = 0.090), smoking status (β = -0.077), SBP (β = 0.117), diastolic blood pressure (DBP) (β = -0.155), low-density lipoprotein cholesterol (β = 0.074), prevalence of antidyslipidemic medication (β = 0.174), and uric acid (β = 0.090) were also significantly and independently associated with HbA1c. Multivariate-adjusted serum HbA1c levels were significantly high in subjects with the lowest serum T-B levels in both genders. Serum T-B is an independent confounding factor for HbA1c among community-dwelling middle-aged and elderly persons.