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Nonclassic actions of vitamin D were first recognized 30 years ago when receptors for active 1, 25-dihydroxyvitamin D3 (1, 25 (OH) 2D3) were detected in various neoplastic cells lines. 1, 2 Other studies immediately following this showed that binding of 1, 25 (OH) 2D3 to the vitamin D receptor (VDR) promoted antiproliferative and prodifferentiation responses in cancer cells, 3, 4 highlighting an entirely new facet of vitamin D action. The spectrum of nonclassic responses to vitamin D was then extended to include actions on cells from the immune system. 5, 6 This interaction was further endorsed by the observation that some patients with the granulomatous disease sarcoidosis present with increased circulating levels of 1, 25 (OH) 2D3 and associated hypercalcemia. 7, 8 In these patients the high serum level of 1, 25 (OH) 2D3 is caused by increased activity of the enzyme 25-hydroxyvitamin D-1a-hydrooxylase (1a …