Vitamin D

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Vitamin D is not actually a vitamin, but a group of fat-soluble prohormones. Vitamins by definition are essential organic compounds which cannot be synthesized by the body and must be ingested; Vitamin D3, cholecalciferol, is synthesized in the skin utilizing UVB rays from the sun.
Vitamin D is most well known for its involvement in keeping bones strong by assisting the absorption of calcium. In the last two decades Vitamin D has been the focus of an enormous amount of research showing that it is involved in neuromuscular and immune functions, reduction of inflammation and modulation of cell growth.
Cholecalciferol is inactive. After being absorbed from food or supplements, or produced in the skin, it is converted to its active form by two hydroxylations. The first is in the liver where it becomes calcifediol (25-hydroxycholecalciferol aka 25-hydroxyvitamin D3 and abbreviated 25(OH)D3). The 25(OH)D3 is then converted in the kidneys to calcitriol (1,25-dihydroxyvitamin D3) or active vitamin D3.
• More than 200 genes are under the control of calcitriol
• Individuals with kidney or liver disease and severe absorption issues may require one or another of the metabolites of vitamin D that are available by prescription
• Obesity may increase the need for vitamin D supplementation and weight loss may reduce the need
• Research suggests vitamin D is directly involved in helping T3 bind to receptors
• Everyone should test vitamin D at least annually
• Many people need to supplement vitamin D
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