"Vitamin D fights cancer: Fact or fiction?"

Currently, there is increasing public awareness that vitamin D can do more than prevent rickets and otherwise improve bone health, but it still remains possible that some claims made in popular articles are poorly substantiated or exaggerated. Skepticism regarding vitamin D as a potential panacea is perhaps generated by the exceedingly high number of health benefits attributed to its ingestion or sunbathing, the anecdotal nature of the evidence in some cases, the lack of agreement on what constitutes the optimal levels of intake, and how exactly vitamin D produces better health. While there is considerable body of evidence suggesting that vitamin D may indeed have beneficial effects on a large spectrum of human disease, in part due to its immuno-regulatory properties, here we focus on the potential mechanisms that can explain how its optimal body levels can reduce the incidence of various human cancers, and on recent clinical studies of the effect of vitamin D and its derivatives on cancer cells. It is already well known that vitamin D can alter cell survival, in some cases inducing death of the malignant cells, and can reduce cell proliferation by blocking cell cycle progression. In addition, a variety of cancer cell types can be induced by vitamin D or derivatives to the more normal, non-proliferating, differentiated cells. This in some cases can be explained by the "Bypass-the-Lesion" hypothesis, according to which vitamin D allows an alternative lineage of cell differentiation of the malignant cells, the normal development of which was blocked by mutations that led to the emergence of the malignant clone, and then to a tumor. Thus, firm molecular grounds are emerging on which we can base our confidence that vitamin D, in an optimal daily dose of about 2,000 IU for most people, is an effective cancer preventive agent.