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Vitamin D: An Evolving Star
By: Peter T. Pugliese, MD
Posted: June 29, 2009, from the July 2009 issue of Skin Inc. magazine.
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In 2006, the Journal of the American Medical Association published a report showing a potential link between vitamin D deficiency and the onset of multiple sclerosis. The authors suggest that this is due to the immune-response suppression properties of vitamin D. It is possible that vitamin D is required to activate an immune response that triggers the mechanism for individuals to recognize self from nonself.11
In tissue cultures, the vitamin D hormone has been found to induce the death of cancer cells. This positive activity of vitamin D is believed to result from its action as a nuclear transcription factor that regulates cell growth, differentiation and programmed cell death, called apoptosis. In addition, vitamin D appears to regulate many cellular mechanisms central to the development of cancer, and again these actions appear to be through the expression of the vitamin D receptor.
There is an increasing body of research that supports the concept that the active form of vitamin D may provide significant protective effects against cancer.12 A study in 2006 found that taking vitamin D (400 international units [IU<sup>c</sup>] per day) cuts the risk of pancreatic cancer by 43% in a test of more than 120,000 people.13 A study involving 1,200 women, published in June 2007, reports that vitamin D at 1,100 IU/day resulted in a 60% reduction in cancer incidence during a four-year clinical trial.14
Vitamin D and the skin
Insight into possible new functions of 1,25-(OH)2D3 beyond the regulation of calcium and phosphorus resulted from studies involving the cellular localization of 1,25-(OH)2D3. The result of this study illustrated that 1,25-(OH)2D3 was localized in the nuclei of the cells in the small intestine, the distal renal tubule of the kidney, the osteoblasts of bone and in tissues not previously considered targets of vitamin D action. In addition, 1,25-(OH)2D3 has been found in the nuclei of the islet cells of the pancreas, keratinocytes of skin, ovarian tissue, mammary epithelium, epithelial cells of the epididymis, neuronal tissue, promyelocytes, macrophages and T lymphocytes—these cells are all blood-derived.
What these new findings mean is that the possibility of 1,25-(OH)2D3 to carry out not only many other functions, but also in cells not even considered as target cells of vitamin D. Other studies followed that showed the vitamin D receptor to be present in the skin,15 thymus and ovarian cells. It is now evident that the vitamin D hormone carries out specific functions in many of these tissues, and many other functions remain to be discovered.