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Vitamin C or L-ascorbic acid is an essential nutrient for humans and certain other animal species, in which it functions as a vitamin. 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), and the entire suborder Anthropoidea (Haplorrhini) (tarsiers, monkeys and apes, including mankind). Ascorbic acid is also not synthesized by guinea pigs and some species of birds and fish. All species which do not synthesize ascorbate require it in the diet. Deficiency in this vitamin causes the disease scurvy in humans.[1][2][3] It is also widely used as a food additive.[4] The pharmacophore of vitamin C is the ascorbate ion. In living organisms, ascorbate is an anti-oxidant, since it protects the body against oxidative stress,[5] and is a cofactor in several vital enzymatic reactions.[6] A recent meta-analysis of 68 reliable antioxidant supplementation experiments, involving a total of 232,606 individuals, concluded that consuming additional ascorbate from supplements may not be as beneficial as thought,[8] though most of these studies so far generally do not evaluate the effects of megadosages at the levels recommended by megadosage activists. Vitamin C is purely the L-enantiomer of ascorbate; the opposite D-enantiomer has no physiological significance. Both forms are mirror images of the same molecular structure. When L-ascorbate, which is a strong reducing agent, carries out its reducing function, it is converted to its oxidized form, L-dehydroascorbate.[6] L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes and glutathione.[9] During this process semidehydroascorbic acid radical is formed. Ascorbate free radical reacts poorly with oxygen, and thus, will not create a superoxide. Instead two semidehydroascorbate radicals will react and form one ascorbate and one dehydroascorbate. With the help of glutathione, dehydroxyascorbate is converted back to ascorbate.[10] The presence of glutathione is crucial since it spares ascorbate and improves antioxidant capacity of blood.[11] Without it dehydroxyascorbate could not convert back to ascorbate.
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