Vitamine D-intoxicatie; echt en onecht

– 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 1,25-(OH)₂D₃ level is low, whereas in pseudo-vitamin D intoxication the 25-OHD₃ content in the serum is normal and the 1,25-(OH)₂D₃ is seriously elevated.

Cultured alveolar macrophages of patients with sarcoidosis can produce 1,25-(OH)₂D₃ as can sarcoid lymph node homogenate. 1,25-(OH)₂D₃ proved to promote the fusion of alveolar macrophages to form polykaryons. Local concentrations of 1,25-(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.