|
Sponsored Links
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), 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 guinea pigs and 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] 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 that the findings should be interpreted with caution).[10] 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.[2] L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes and glutathione.[11] 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.[12] The presence of glutathione is crucial since it spares ascorbate and improves antioxidant capacity of blood.[13] Without it dehydroxyascorbate could not convert back to ascorbate.
|
