OR13-01 Comparison of Vitamin D Metabolism in Deficient and Sufficient States

Objective: to study the differences in calcium-phosphorus and vitamin D metabolism in healthy individuals with deficient and sufficient baseline state of vitamin D. Materials and methods: The study included 16 young conditionally healthy individuals, divided into two equal groups: with levels of 25(OH)D below and above 30 ng/ml determined by the immunochemiluminescent method (Group A and Group B respectively; DEQAS certified). All participants were evaluated for the biochemical parameters of blood and urine, characterizing calcium-phosphorus metabolism, PTH by commercial methods, and vitamin D metabolites (25(OH)D3, 25(OH)D2, 3-epi-25(OH)D3 and 24,25(OH)2D3) by HPLC/MS-MS before oral intake of 150 000 IU of an aqueous solution of cholecalciferol and 7 days after administration. Results: At baseline, the level of vitamin D metabolite 25(OH)D2 in Group B was lower with no significant differences in other studied parameters. In group A, strong positive correlations were observed between levels 25(OH)D3 and 3-epi-25(OH)D3, 24,25(OH)2D3, while in group B there were no such associations. After taking a loading dose of cholecalciferol, the groups showed generally similar changes in the studied vitamin D metabolites: a statistically significant increase in 25(OH)D3, 3-epi-25(OH)D3, a decrease in 25(OH)D2, and a ratio of 24,25(OH)2D3 to 25(OH)D3. However, the level of 24,25(OH)2D3 did not change in group B, with a significant increase in group A. The medians of the studied biochemical parameters in blood/urine, as well as PTH, remained unchanged in both groups. Conclusion: In patients with inadequate baseline levels of 25(OH)D, after a loading dose of cholecalciferol, there is a tendency to formation of more inactive forms of vitamin D. These deviations in the metabolism of vitamin D need to be clarified, since they can potentially affect the effectiveness of cholecalciferol therapy.