Vitamin D (cholecalciferol) is a pre hormone that has long been known for its important role in regulating body levels of calcium and phosphorus, and in mineralization of bone.
More recently, it has become clear that receptors for vitamin D are present in a wide variety of cells, and that vitamin D has biologic effects which extend far beyond control of mineral metabolism.
It is believed that vitamin D plays an important part in the regulation of genes involved in cell growth, differentiation and proliferation. By promoting differentiation and inhibiting proliferation, vitamin D may become an important factor in cancer prevention and therapy.
Through its regulation of genes, vitamin D controls the production of immune factors known as lymphokines, which effect cell-mediated immunity functions.
Vitamin D may play a role in the prevention and/or treatment of the following health conditions:
- Atherosclerosis
- Breast cancer
- Colon cancer
- Depression
- Epilepsy
- Hypertension
- Inflammatory bowel disease
- Kidney diseaseLiver disease
- Multiple sclerosisOsteoporosis
- Periodontal disease
- Preeclampsia
- Prostate cancer
- Psoriasis
- Skin cancer
- Tinnitus
- Ulcerative colitis
Contrary to common belief, vitamin D is NOT actually a vitamin at all. "Vitamins" by definition, are nutrients that CANNOT be produced by the body, but are NECESSARY for the proper functioning of the body's tissues and organs. Vitamin D is ESSENTAL for calcium and phosphorus metabolism, and IS required for the normal development of healthy bones and teeth, but as it IS produced by our bodies (when our skin is exposed to ultraviolet rays from the sun) technically, it can NOT be considered a vitamin.
Vitamin D was originally classified as a vitamin because of the findings of a British researcher in1920, who raised dogs in the winter (without any exposure to sunlight or ultraviolet rays). He found that the animals developed rickets (a bone disease) unless fed a diet containing fish-liver oils. He wrongly concluded that the fat soluble substance needed for developing bones was not found naturally in the body and so was a "vitamin". In 1924 researchers discovered that exposing skin to sunlight resulted in the body's own production of this so-called "fat-soluble vitamin". Despite the misnomer, for nutritional and public health reasons, vitamin D continues to be officially classified as a "vitamin".
There are two basic types of vitamin D.
1. In plants, Vitamin D2 (ergocalciferol) is converted from it's basic building block (ergosterol) when ultraviolet light from the sun hits the leaf.
2. In humans, Vitamin D3 (cholecalciferol) is converted from it's basic building block (cholesterol) when ultraviolet light hits the cells of our skin.
Vitamins D2 and D3 (usually referred to as "provitamin D") do not have significant biological activity. Rather, both must be metabolized, first by the liver and then by the kidneys into the converted, fully-active, hormonal form of vitamin D (calcitrol).
Although the current RDA for vitamin D is 400 iu, recent studies have shown that the optimal intake of vitamin D is about 4,000- 6,000 iu a day. This results in a circulation concentration of the fully-active form of vitamin D in the amount of 100-125 nmol/litre. This level seems to be required for the proper functioning of all vitamin D-dependent systems. This amount is well below the "no observed adverse effect level" which is conservatively placed at 10,000 iu/day and thus such supplementation is safe for anyone who is not hypersensitive to vitamin D. Other researchers includng Robert Barefoot have suggested doses as high as 30,000 iu/day.
Most brands on the market contain 200 to 400 iu of vitamin D per capsule. D-Max contains a whopping 5,000 iu per capsule.