Vitamin D Metabolism in Man

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Abstract
This study evaluated the effects of acute intravenous calcium supplementation on vitamin D metabolism in nine patients maintained on long-term prednisone therapy for chronic obstructive lung disease. Vitamin D turnover studies, employing 1,2-3H,414C vitamin D3and coincident measurement of serum 25-hydroxycholecalciferol (25-OHCC) concentrations demonstrated that intravenous calcium administration decreased the mean 25-OHCC concentration (P<.05) and half-time (P<.05) in the prednisone-treated patients when compared with the mean 25-OHCC concentration and half-time found in these patients prior to calcium infusion. However, there was no significant difference in the amounts of 24,25-dihydroxycholecalciferol (24,25-(OH)2CC) or 1,25-dihydroxycholecalciferol (1,25-(OH)2CC) appearing after calcium infusion. The results of the study showed that the intravenous administration of calcium to corticosteroidtreated patients accelerated the disappearance of 25-OHCC from the plasma of these patients without parallel increases in the production of 1,25-(OH)2CC or 24,25-(OH)2CC. (Arch Intern Med136:1241-1248, 1976)