Vitamin D3: The New "Miracle Supplement"?
We all know of Vitamin D's importance in calcium absorption and bone health, but did you know that Vitamin D is not actually a Vitamin, but one of the most potent hormones for regulating cell growth, gene expression, and primary and acquired immunity. Solar UV-B wave irradiation of cholesterol in the skin is the primary source of Vitamin D other than dietary supplements and dietary sources such as oily fish, including salmon, mackerel, sardines, cod liver, eggs, milk, cereals, orange juice, and yogurt. There are two forms of Vitamin D: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). UV-B radiation triggers conversion of cholesterol (pro-Vitamin D3) to pre-Vitamin D3 in the plasma membrane of human skin cells. Pre-Vitamin D3 is rapidly converted to Vitamin D3 by the skin's temperature. Vitamin D3 undergoes two sequential hydroxylation's, first in the liver and then in the kidney, to form the biologically active form 1,25-dihydroxyvitamin D. Melanin in skin pigmentation as well as sunscreens can greatly reduce the UV-B mediated cutaneous synthesis of Vitamin D. Irregular intake of Vitamin D can cause chronic vitamin D inadequacy, which currently constitutes a wide epidemic in many populations.
The small intestine, kidneys and bones are the primary organs which are responsive to Vitamin D, involving mineral metabolism and effecting skeletal health. However we now know that there are Vitamin D receptors in other tissues and organs as well,
that are quite important in extra-skeletal health. The Vitamin D receptor is a steroid hormone nuclear receptor, and when bound to Vitamin D mediates gene regulation. Vitamin D receptors have also been isolated from tissues and organs such as heart, stomach, pancreas, brain, skin, gonads, muscle, various cells of the immune system including T and B lymphocytes, breast, colon, and prostate. Most tissues and cells not only express the Vitamin D receptor, but also express the same enzyme as the kidney (1 alpha-hydroxylase). Indeed it has been postulated that most cells locally produce Vitamin D to help regulate a variety of cell functions, including growth and differentiation, explaining why epidemiologically, reduced sun exposure at lower altitudes is related to a variety of chronic diseases. As noted in the Mayo Clinic article "Nutrition And Chronic Disease" in March 2006: "Each tissue can make what it currently needs for itself and all that is required is an adequate availability of the precursor serum 25-hydroxyvitamin D".
Evidence suggests that Vitamin D helps to regulate cell growth and prevent cancer progression in seventeen different types of cancer, as noted in a recent article in November 2006 in the Internal Medicine World Report (www.imwr.com). Indeed in that article it was noted that the current recommendation of 400 I.U. per day is insufficient to prevent Vitamin D deficiency. By regulating cell growth it is thought that Vitamin D prevents cancer progression by reducing angiogenesis ( blood vessel formation), increasing cell differentiation into normal healthy cells, reducing cell proliferation and metastases, and causing apoptosis of cancer cells (cellular death). Several studies have shown that cancer cells in the breast, colon, prostate, bone and melanomas are responsive to the anti-proliferative effects of Vitamin D, and that higher levels of Vitamin D are associated with reduced cancer incidence and decreased cancer mortality. Furthermore, concerning neuromuscular effects, Vitamin D has been shown to improve muscle mass, muscle strength and better balance. There is also increasing evidence that inadequate Vitamin D levels contribute to the pathogenesis and progression of hypertension, cardiovascular disease, Type 2 diabetes and heart failure.
Concerning the immunomodulatory effects of Vitamin D, recent evidence has shown an effect on such diseases as multiple sclerosis, Type 1 diabetes, psoriasis, rheumatoid arthritis, inflammatory bowel disease including Crohn's disease, systemic lupus erythematosus, and periodontal disease. In fact, as noted in the June 15 edition of the Internal Medicine News (www.internalmedicinenews.com), "Lupus patients have extremely low levels of Vitamin D." Interestingly enough it was noted in a recent abstract in the Journal of the American Medical Association (July 2008) from the Archives Of General Psychiatry that there is "an association of depression status and severity with decreased serum 25-hydroxyvitamin D."
Vitamin D inadequacies have been reported in approximately 36% of healthy young adults and 57% of general medical inpatients in the United States which is even higher in Europe. Contributing factors are low sunlight exposure, decreases in synthesis of Vitamin D in the skin, and diets low in Vitamin D. Supplemental doses as well as sensible sun exposure could prevent this deficiency in many populations. The current thinking is that the daily recommendations of Vitamin D are insufficient and it has been suggested that amounts of up to 1000 International Units per day and maybe even more may be necessary to maintain adequate Vitamin D levels. To learn more please refer to a recent article in March of 2006 in The Mayo Clinic Proceedings at www.mayoclinicproceedings.com
Best in Health,
David M. Rekar, M.D.
Medical Director
["A daily dose of Vitamin D" and "Sun rays in the city" Images Thanks To carlafida at Flickr.com.]
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