[Current Topics on Vitamin D. Anti-cancer effects of vitamin D]

Epidemiological studies have revealed that vitamin D deficiency increases the risk of cancer development and is associated with its poor prognosis. In the classical view of calcium metabolism, vitamin D is activated by CYP27B1 in the kidney and promotes calcium absorption in the intestine as a hormone. Besides such a classical role, vitamin D is known to exert multiple extra-skeletal actions through CYP27B1 and vitamin D receptor (VDR) that is expressed in a wide variety of extra-renal tissues and cell types. As one of its "non-classical" actions, vitamin D has been shown to have anti-cancer activity by various mechanisms including inhibition of cellular proliferation, induction of apoptosis, stimulation of differentiation, suppression of tumor invasion, metastasis, and angiogenesis. Despite numerous promising results at the cellular and animal levels, clinical trials have so far failed to provide definitive evidence for anti-cancer effect of vitamin D.