A vitamin is an organic compound required in tiny amounts for essential metabolic reactions in a living organism.[1] The term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but that are not essential for life. 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 is 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 group - methyl, formyl and methylene - in the cell.
