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What Does Vitamin D-3 Do?

By Stephen Christensen

Vitamin D-3, or cholecalciferol, is a fat-soluble vitamin which is synthesized in your skin whenever you are exposed to sunlight. Once formed, cholecalciferol is processed in your liver and kidney to produce the biologically active form of vitamin D, 1,25-dihydroxyvitamin D-3, or 1,25(OH)2D-3. Vitamin D is available as a supplement in two different forms. Vitamin D2, or ergocalciferol, is derived from plants, so vegans prefer it, but vitamin D-3 has been proven to be more potent in humans according to the June 2012 issue of "The American Journal of Clinical Nutrition." Vitamin D-3 serves a variety of important functions in your body.

Vitamin D-3 Receptors Are Widespread

Vitamin D receptors, or VDRs, are present in most cells and tissues in your body, according to research published in the October 2009 issue of the German-language journal, “Medizinische Monatsschraft für Pharmazeuten.” When stimulated by vitamin D-3, VDRs trigger specific genes in your cells’ chromosomes, thereby regulating cellular activity. The discovery of VDRs in so many tissues implies a role for vitamin D in a wide array of bodily functions, many of them not yet discovered.

Vitamin D-3 in Bone Development

Vitamin D-3’s role in calcium metabolism and bone development is an important one, according to the Linus Pauling Institute. Vitamin D-3 stimulates the absorption of calcium from your intestine and the retention of calcium by your kidneys, and it increases the activity of osteoblasts, which are cells that synthesize bone. Vitamin D-3 deficiency leads to rickets in developing children, which is characterized by soft, malformed bones. In adults, vitamin D-3 deficiency causes loss of bone mass, which contributes to osteoporosis.

Immunity and Vitamin D-3

A December 2004 review in “The American Journal of Clinical Nutrition” demonstrates vitamin D-3’s importance in immune function. VDR receptors are present in your white blood cells, and stimulation of these receptors, guides your immune response. According to the review’s authors, vitamin D-3 deficiency increases your risk for autoimmune diseases, such as Crohn’s disease. Your risk for certain infections, such as tuberculosis, may also be increased by vitamin D-3 deficiency, according to research published in the January 2011 “Nature Reviews. Endocrinology.” Finally, researchers are learning that sufficient production or consumption of vitamin D-3 may help to prevent cancers of the breast, colon, pancreas, prostate, ovary and kidney, according to research published in the July 2009 “Annals of Epidemiology.”

Considerations and Recommendations

Vitamin D-3 exerts many important physiologic effects in addition to its well-defined role in calcium metabolism. In a manner similar to many hormones, vitamin D-3’s activity is governed by receptors which are present in most of your tissues. Many of vitamin D-3’s functions remain to be identified. Daily vitamin D-3 requirements vary from 200 to 600 International Units, depending on your age. Many supplements are available in doses up to 2,000 International Units, and the Linus Pauling Institute reports that 4,000 International Units is the safe, tolerable upper limit. If you take a supplement, consider the amount of time you spend in the sun before you settle on a dosage. To make sure you are getting enough -- but not too much -- partner with your doctor and discuss your diet, sun habits and the possibility of checking your body's D-3 level with a blood test.

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