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Vitamin D is a steroid 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 this hormone has biologic effects which extend far beyond control of mineral metabolism.
The term vitamin D actually refers to a group of steroid molecules. Vitamin D3, also known as Cholecalciferol is generated in the skin of animals when light energy is absorbed by a precursor molecule 7-dehydrocholesterol. Vitamin D is thus not a true vitamin, because individuals with adequate exposure to sunlight do not require dietary supplementation. There are dietary sources of vitamin D, including egg yolk, fish oil and a number of plants. The plant form of vitamin D is called Vitamin D2 or Ergosterol. However, natural diets typically do not contain adequate quantities of vitamin D, and exposure to sunlight or consumption of foodstuffs purposefully supplemented with vitamin D are necessary to prevent deficiencies.
Vitamin D from the diet, or from skin synthesis, is biologically inactive. It is activated by two protein enzyme hydroxylation steps, the first in the liver and the second in the kidneys. As vitamin D can be synthesized in adequate amounts by most mammals if exposed to sufficient sunlight, it is not essential, so technically not a vitamin. Instead it can be considered a hormone, with activation of the vitamin D pro-hormone resulting in the active form, calcitriol, which then produces effects via a nuclear receptor in multiple locations.
Cholecalciferol is converted in the liver to calcifediol (25-hydroxycholecalciferol); ergocalciferol is converted to 25-hydroxyergocalciferol. These two vitamin D metabolites (called 25-hydroxyvitamin D or 25(OH)D) are measured in serum to determine a person's vitamin D status. Calcifediol is further hydroxylated by the kidneys and some of the immune system cells to form calcitriol (also known as 1,25-dihydroxycholecalciferol), the biologically active form of vitamin D. Calcitriol circulates as a hormone in the blood, having a major role regulating the concentration of calcium and phosphate, and promoting the healthy growth and remodeling of bone. Calcitriol also has other effects, including some on cell growth, neuromuscular and immune functions, and reduction of inflammation.
There are numerous benefits that can be attributed to Vitamin D, including strengthening of bones and connective tissue, aiding in the healing of wounds, and increasing the performance of the immune system. Perhaps one of Vitamin D's best attributes is its amazing anti-oxidant ability. It protects the fluids of the body such as blood from damage by free radicals. By strengthening arterial walls, it also plays an important role in maintaining a healthy blood pressure, as well as reducing tissue damage.
Vitamin D protects the cells of the body and may prevent damage caused to them by cancer, heart disease, aging, and arthritis. Some studies printed in the Journal of Strength and Conditioning Research have shown that taking Vitamin D in doses of 1000 mg per day reduced the secretion of cortisol, allowing one?s muscles to grow and lift better. There is a multitude of clinical studies that have been conducted substantiating Vitamin D's powerful effects. We know it works for a variety of ailments and we know it works well! Some studies even show that Vitamin D reduces one?s stress level.
Vitamin D deficiency or insufficiency occurs in several other situations, which you might predict based on the synthetic pathway described above:
Dosage: 400IU is the needed dose, 1000 is usually the maximum, but we advocate the use of an 2000IU's for most individuals because of todays seditary life style. Mega dosing is only used in medical treatment and only under medical supervision.
Stacks well with: Vitamin A, Calcium, Creatine, Phosphorus.
Food Sources: Tuna, mackerel, butter, sardines, salmon, kipper, egg-yolks and liver.
Vitamin D toxicity: Excessive exposure to sunlight does not lead to overproduction of vitamin D. Vitamin D toxicity is inevitably the result of overdosing on vitamin D supplements. Don't do this! Ingestion of milligram quantities of vitamin D over periods of weeks of months can be severely toxic to humans and animals. In fact, baits laced with vitamin D are used very effectively as rodenticides(poison).
Vitamin D is constantly being studied today against many of the viruses and ailments of todays more toxic world. We will update our page as studies bring us the latest and most accurate information.