Evidence for abnormal regulation of circulating 1 alpha,25-dihydroxyvitamin D in patients with sarcoidosis and normal calcium metabolism.

The effects of vitamin D, 2.5 mg (100,000 U)/d for 4 d, on serum calcium, serum 25-hydroxyvitamin D (25-OHD), and serum 1 alpha,25-dihydroxyvitamin D [1 alpha,25(OH)2D] were compared in 17 normal subjects and 6 patients with sarcoidosis who had normocalcemia and no history of hypercalcemia. The diagnosis was confirmed histologically in each of them. Vitamin D increased mean serum 25-PHD from 30 +/- 4 to 99 +/- 15 ng/ml (P < 0.001) and did not change mean serum 1 alpha,25(OH)2D (32 +/- 3 vs. 29 +/- 3 pg/ml) or mean serum calcium (9.5 +/- 0.1 vs. 9.6 +/- 0.1 mg/dl) in the normal subjects. In contrast, vitamin D increased mean serum 25-OHD from 19 +/- 3 to 65 +/- 19 ng/ml (p < 0.05), increased mean serum 1 alpha,25(OH)2D threefold from 40 +/- 7 to 120 +/- 24 pg/ml, and increased mean serum calcium from 9.4 +/- 0.2 to 9.8 +/- 0.2 mg/dl (P < 0.01). There was a significant positive correlation between the serum 1 alpha,25(OH)2D and serum calcium in these individuals (r = 0.663, P < 0.01) but not in the normal subjects. The results (a) provide further evidence for abnormal regulation of circulating 1 alpha,25(OH)2D in sarcoidosis and (b) indicate that the abnormality may exist in patients with normal calcium metabolism. Thus, the defect in vitamin D metabolism in sarcoid apparently is more common than was previously recognized.

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