Vitamin C

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Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species, in which it functions as a vitamin. In living organisms, ascorbate is an anti-oxidant, since it protects the body against oxidative stress.[1] It is also a cofactor in at least eight enzymatic reactions, including several collagen synthesis reactions that cause the most severe symptoms of scurvy when they are dysfunctional.[2] In animals, these reactions are especially important in wound-healing and in preventing bleeding from capillaries.

Ascorbate (an ion of ascorbic acid) is required for a range of essential metabolic reactions in all animals and plants. It is made internally by almost all organisms; notable mammalian group exceptions are most or all of the order chiroptera (bats), guinea pigs, capybaras, and one of the two major primate suborders, the Anthropoidea (Haplorrhini) (tarsiers, monkeys and apes, including human beings). Ascorbic acid is also not synthesized by some species of birds and fish. All species that do not synthesize ascorbate require it in the diet. Deficiency in this vitamin causes the disease scurvy in humans.[3][4][5] It is also widely used as a food additive.[6]

Scurvy has been known since ancient times. People in many parts of the world assumed it was caused by a lack of fresh plant foods. The British Navy started giving sailors lime juice to prevent scurvy in 1795.[7] Ascorbic acid was finally isolated in 1932 and commercially "synthesized" (this included a fermentation step in bacteria) in 1934. The uses and recommended daily intake of vitamin C are matters of on-going debate, with RDI ranging from 45 to 95 mg/day. Proponents of megadosage propose from 200 mg to more than 2000 mg/day. The fraction of vitamin C in the diet that is absorbed and the rate at which the excess is eliminated from the body vary strongly with the dose. Large, randomized clinical trials on the effects of high doses on the general population have not been conducted.

Routine vitamin C supplementation does not reduce the incidence of the common cold in the general population.[8][9] In one study vitamin C supplementation significantly reduced the frequency of the common cold but without apparent effect on the duration or severity (however the authors of this research pointed out that the findings should be interpreted with caution).[10] As early as 1984 researchers knew that supplementation of drinking water with vitamin C increased the average life span of mice by as much as 20 percent.[11]

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