Association between serum 25-hydroxyvitamin D concentrations and urinary vitamin D metabolite concentrations measured by the NLucVDR assay

It is well known that vitamin D is essential for human health; however, many people suffer from vitamin D deficiency or insufficiency worldwide, including in Japan. Serum 25-hydroxyvitamin D (25(OH)D) concentrations are typically measured to evaluate vitamin D status. In a previous study, we demonstrated that the concentrations of vitamin D metabolites in urine, measured using the NLucVDR assay system composed of a splittype nanoluciferase and the ligand-binding domain (LBD) of the human vitamin D receptor, correlated with serum 25(OH)D concentrations measured using liquid chromatography-mass spectrometry (LC-MS) or electrochemiluminescence immunoassays (ECLIAs). However, the number of participants was limited to 23. In the present study, we investigated the relationship between urinary vitamin D metabolite concentrations measured using the NLucVDR assay and serum 25(OH)D concentrations measured using ECLIA in 292 healthy individuals aged 20-69 years. We observed a significant positive correlation between 25(OH)D concentrations and urinary vitamin D metabolite concentrations (r = 0.400, p < 0.001). Furthermore, in a multiple regression model with serum 25(OH)D concentrations as the dependent variable and urinary vitamin D metabolite concentrations, sex, age, body mass index (BMI), and vitamin D intake as independent variables, urinary vitamin D metabolite concentrations showed a significant positive association with serum 25(OH)D concentrations regardless of sex, age, BMI, and vitamin D intake. Additionally, receiver operating characteristic (ROC) curve analysis was performed to evaluate whether this multiple regression model could predict vitamin D deficiency. The area under the curve (AUC) was 0.743 and 0.708 for women and men with vitamin D deficiency (serum 25(OH)D < 20 ng/ mL), respectively. Our results suggest that urinary vitamin D metabolite concentrations, measured by the NLucVDR assay, may be useful for the noninvasive predictive tool of vitamin D deficiency.