Background: Bilirubin may exert antioxidant and cytoprotective effects by scavenging peroxyl radicals and inhibiting oxidation. There is evidence that middle-aged and elderly patients with type 2 diabetes mellitus (T2DM) have abnormal bone metabolism and deterioration of bone microstructure, which can easily lead to increased bone fragility and osteoporosis. However, few studies have reported whether total bilirubin (TB) is associated with bone metabolism in middle-aged and elderly T2DM patients. We collected 10 years of data from the NHANES database to examine the association between TB and bone mineral density (BMD) in the US population of T2DM patients older than 50 years.
Methods: The population data in this study were obtained from five cycles of the NHANES database (2005-2006, 2007-2008, 2009-2010, 2013-2014, and 2017-2018) with a total of 50,464 subjects. The outcomes of interest were total femur BMD and lumbar BMD. The relationship between TB and BMD was analyzed using weighted multiple linear regression, subgroup analysis, generalized additive models, smoothed fitted curves, and two-part logistic regression.
Results: A total of 1609 individuals (mean age 63.78 years; 60.99% Caucasian) were available for final data analysis based on strict eligibility criteria. After complete correction for potential confounders, no association was found between TB and BMD. However, in other racial populations (mainly non-Hispanic Asians), TB levels were positively associated with both BMDs [total femur BMD, β (95% CI), 0.005 (0.000, 0.010); lumbar BMD, β(95% CI), 0.005 (0.000, 0.009)]. In addition, no interactions were observed based on all priori stratification.
Conclusions: This study demonstrates that TB levels are not associated with BMD when the effect of underlying liver disease is excluded in a nationally representative population of T2DM over 50 years of age in the United States. However, in Asian populations, TB levels appear to be positively associated with BMD.