Vitamins are nutrients required in tiny amounts for essential metabolic reactions in the body. There are two types of vitamins: fat soluble and water soluble. When you eat foods that contain fat-soluble vitamins, the vitamins are stored in the fat tissues in your body and in your liver. They go and wait around in your body fat until your body needs them.
Vitamins are bio-molecules that act both as catalysts and substrates in chemical reactions. When acting as a catalyst, vitamins are bound to enzymes and are called cofactors. (For example, vitamin K forms part of the proteases involved in blood clotting.) Vitamins also act as coenzymes to carry chemical groups between enzymes. (For example, folic acid carries various forms of carbon groups methyl, formyl or methylene in the cell)
Until the 1900s, vitamins were obtained solely through food intake. Many food sources contain different ratios of vitamins. Therefore, if the only source of vitamins is food, changes in diet will alter the types and amounts of vitamins ingested. Disease caused by a deficiency of fat-soluble vitamins (A, D and E) has always been rare. Levels of water-soluble vitamins (all B vitamins and C) can become deficient state in the body in a matter of days (hours in the case of drug-induced deficiencies), but the effects (Scurvy, in the case of an Ascorbate deficiency) may not display for weeks. When the cause of a disease is not microbial, then a major alternate diagnosis is a deficiency in what is needed.
Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades, allowing supplementation of the dietary intake
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