Studies of the hypercalcaemia of sarcoidosis: Effect of steroids and exogenous vitamin D₃ on the circulating concentrations of 1,25-dihydroxy vitamin D₃

Hypercalcemia in 6 patients with sarcoidosis was associated with elevated circulating 1,25-dihydroxy vitamin D₃ (187-475 pmol/l): the concentration of this metabolite of vitamin D was a function of the concentration of its precursor, 25-hydroxy vitamin D which remained within the normal range. Corticosteroids, in reducing serum calcium, eliminated this abnormal substrate-product relationship by rapidly reducing circulating 1,25-dihydroxy vitamin D₃ while having no effect on 25-hydroxy vitamin D. The fall in circulating 1,25-dihydroxy vitamin D₃ preceded the fall of calcium. Studies on the clearance of exogenous 1,25-dihydroxy vitamin D₃ indicated that during hypercalcemic episodes, the plasma disappearance time of the sterol was delayed and that this reverted to normal with steroid therapy. Administration of vitamin D₃ to these patients with sarcoidosis increased the circulating concentration of 1,25-dihydroxy vitamin D₃ and this resulted in hypercalcemia, thus accounting for their hypersensitivity to vitamin D and sunlight.