Evidence that Increased Circulating 1_α,25-Dihydroxyvitamin D is the Probable Cause for Abnormal Calcium Metabolism in Sarcoidosis

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Abstract

Mean plasma 1α,25-dihydroxyvitamin D[1α,25(OH)2D] was significantly increased and serum parathyroid hormone was suppressed in three patients with sarcoidosis and hypercalcemia. Prednisone lowered the mean plasma 1α,25(OH)2D to normal range and corrected the hypercalcemia. To elucidate the mechanism for the increased sensitivity to vitamin D in this disorder, the effects of orally-administered vitamin D2 were determined in seven normal subjects, four patients with sarcoidosis and normal calcium metabolism and three patients with sarcoidosis and a history of hypercalcemia who were normocalcemic when studied. Serum and urinary calcium, serum 25-hydroxyvitamin D (25-OHD), plasma 1α,25(OH)2D and, in some studies, calcium balance were measured. Vitamin D2, 250 μg a day for 12 d, produced little, if any, change in mean plasma 1α,25(OH)2D and in urinary calcium in the normals and in the patients with normal calcium metabolism. In contrast, vitamin D2 produced increases in plasma 1α,25(OH)2D from concentrations which were within the normal range (20-55 pg/ml) to abnormal values and increased urinary calcium in two patients with abnormal calcium metabolism. In an abbreviated study in the third patient, vitamin D2, 250 μg a day for 4 d, also increased plasma 1α,25(OH)2D abnormally from a normal value. There was a highly significant correlation between plasma 1α,25(OH)2D and urinary calcium. Serum 25-OHD and serum calcium remained within the normal range in all subjects and patients. These findings provide evidence that the defect in calcium metabolism in sarcoidosis probably results from impaired regulation of the production and(or) degradation of 1α,25(OH)2D. Prednisone may act to correct the abnormal calcium metabolism by reducing circulating 1α,25(OH)2D.

Authors

Norman H. Bell, Paula H. Stern, Elizabeth Pantzer, Tushar K. Sinha, Hector F. Deluca