Endocrine Abstracts

Background: Vitamin D is a dietary micronutrient responsible for calcium and phosphorus metabolism and multiple extraskeletal actions. The assessment of vitamin D status is commonly based on measurement of 25(OH)D total concentration in serum. However, the usage of LC-MS/MS analytical technique allows to reliably assess a panel of vitamin D metabolites in serum or plasma, which may help to investigate the metabolic paths of vitamin D, especially in populations at risk of deficiency.

Methods: A randomized, two-arms, open study was conducted on 58 patients (28 female and 30 male; aged from 61 to 96 years old). The primary aim was to assess the effects of a single, high, oral dose of vitamin D₃ (120.000 IU) on serum 25(OH)D₃, 25(OH)D₂, 24,25(OH)₂D₃, 3-epi-25(OH)D₃ and 1,25(OH)₂D₃ concentrations (measured by LC-MS/MS), calculated 24,25(OH)₂D₃/25(OH)D₃ ratio and 25(OH)D₃/3-epi-25(OH)D₃ ratio at baseline, 3 days and 7 days after administration, compared to control group. The secondary aim was assessment of influence of percentage of fat tissue on serum metabolites of vitamin D and their changes after bolus dose.

Results: 56.6% study group attained a serum 25(OH)D₃ concentration >30 ng/ml. All subjects, except for one patient achieved a serum 25(OH)D₃ concentration >20 ng/ml after administration. No one exceed reference value of vitamin D (30–50 ng/ml). Among participants who received vitamin D₃ there were significant increase in 25(OH)D₃, 3-epi-25(OH)D₃, 1,25(OH)₂D₃, 24,25(OH)₂D₃ on 3rd day after administration. 24,25(OH)₂D₃ concentration gradually grew, achieving the highest concentration on 7th day. The percentage increase of 25(OH)D₃ was negatively correlated with baseline 25(OH)D₃ (r=-0.688, P = 0.001). Positive correlation between percentage increase in 25(OH)D₃ and a percentage increase serum concentration of 24,25(OH)₂D₃ (r=0.954, P< 0.001), 3-epi-25(OH)D₃ (r=8.03, P<0.001) and 1,25(OH)₂D₃ (r=0.789, P<0.001) were found. None of the study participants developed hypercalcemia. The baseline concentration of analyzed metabolites of vitamin D in serum and their percentage increase were neither dependent on BMI nor percentage of fat tissue.

Conclusions: High dose of vitamin D rapidly increases 25(OH)D₃ concentration in the elderly patients. The response to the bolus of vitamin D includes activation of 3-epimerase, followed by production of 24,25(OH)₂D₃, which protects from excessive increase of active form of vitamin D.