Vitamin D-Binding Protein Clearance Ratio Is Significantly Associated with Glycemic Status and Diabetes Complications in a Predominantly Vitamin D-Deficient Population

INTRODUCTION: Studies have shown increased urine excretion of vitamin D-binding protein (VDBP) in patients with diabetic nephropathy (DN) resulting from postulated mechanisms linked to renal tubular damage. In this study, we evaluate the utility of VDBP clearance ratio as a novel determinant of glycemic status, DN, and other diabetes-associated complications. METHODS: Levels of vitamin D, HbA1c, serum, urine concentrations of VDBP, and creatinine were measured in 309 subjects. The ratio of urine microalbumin to creatinine was determined to categorize subjects as normoalbuminuric (NAO), microalbuminuric (MIA), and macroalbuminuric (MAA). The VDBP clearance ratio was calculated. RESULTS: Mean VDBP clearance ratios in NAO, MIA, and MAA were 0.7, 4, and 15, respectively. Significant positive correlations of VDBP clearance ratio were found with age, WC, SBP, DBP, TG, glucose, HbA1c, urine VDBP, urine microalbumin, and urine microalbumin/creatinine, and a significant negative correlation was found with the steady-state estimate of beta cell function (B%). Receiver operating curve (ROC) analyses of the use of VDBP clearance ratio for detection of albumin status shows a value of 0.81 for the area under the curve. CONCLUSIONS: The strong associations of VDBP clearance ratio with glycemic control and diabetes-associated complications suggest that this index could play a wider role in detection and/or pathogenesis and complications of diabetes.