[Vitamin D poisoning; real and spurious].

Vitamin D in large doses is a proper therapy in hypoparathyroidism, osteomalacia, vitamin D-resistant rickets and also in chronic renal failure although in those cases the active metabolite of vitamin D is preferred because of the much shorter biologic halflife. Apart from these disorders there are no good reasons for using megadoses of vitamin D. Pseudo-vitamin D intoxication is caused by granulomatous diseases as a so-called inappropriate calcitriol secretion. In cases of vitamin D intoxication the 25-OHD3 content in the serum is much too high, the parathyroid hormone concentration is suppressed and the I,25-(OH)2D3 level is low, whereas in pseudo-vitamin D intoxication the 25-OHD3 content in the serum is normal and the I,25-(OH)2D3 is seriously elevated. Cultured alveolar macrophages of patients with sarcoidosis can produce I,25-(OH)2D3 as can sarcoid lymph node homogenate. I,25-(OH)2D3 proved to promote the fusion of alveolar macrophages to form polykaryons. Local concentrations of I,25-(OH)2D3 may be higher at sites of granulomatous tissue and can act in a paracrine or autocrine fashion to enhance granuloma formation. The action of glucocorticoids and chloroquine in patients with sarcoidosis and hypercalcaemia is presumably an interruption of the described vicious circle.