Biomarkers of Vitamin D Sufficiency: Vitamin D Metabolite Levels do not depend on 25-Hydroxyvitamin D2 levels in Healthy Turkish Individuals

Patient-specific factors may influence the adequate supplemental vitamin D dose. In this study, we evaluated the relationship between 25(OH)D(2 )and free vitamin D levels and vitamin D deficiency in a healthy Turkish population. Method: Blood samples were obtained from 92 healthy adults aged >= 18 years. Total 25(OH)D was determined by CMIA. Serum 25(OH)D-3 and D(2 )levels were measured by LC-MS. Free 25(OH)D was calculated according to the Bikle method. Results: In 54% of the participants, 25(OH)D(3)levels were below 20 ng/mL. Those with 20 ng/mL or higher had higher mean serum 25(OH)D(3)and free vitamin D levels (P<0.001). Mean 25(OH)D(2)concentration did not differ according to deficiency criteria. Serum 25(OH)D2 levels were consistent regardless of free vitamin D concentrations. Conclusions: Serum 25(OH)D-3 and free vitamin D concentrations measured by LC-MS indicate deficiency by influencing the total 25(OH)D(3)concentration. However, serum 25(OH)D(2 )concentration did not differ between individuals and does not directly indicate deficiency.