Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient An essential nutrient is a nutrient required for normal body functioning that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health , and thus must be obtained from a dietary source. Essential nutrients are also defined by the collective physiological evidence for their importance in the diet, for humans Humans, known taxonomically as Homo sapiens , are the only living species in the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo and certain other animal species, in which it functions as a vitamin A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For. In living organisms, ascorbate is an anti-oxidant An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions that damage cells. Antioxidants terminate these chain reactions by, since it protects the body against oxidative stress Oxidative stress is caused by an imbalance between the production of reactive oxygen and a biological system's ability to readily detoxify the reactive intermediates or easily repair the resulting damage. All forms of life maintain a reducing environment within their cells. This reducing environment is preserved by enzymes that maintain the.^[1] It is also a cofactor A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes, and cofactors can be considered "helper molecules" that assist in biochemical transformations. Cofactors can also be classified depending on how tightly they bind to an in at least eight enzymatic Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their reactions, including several collagen Collagen is a group of naturally occurring proteins. In nature, it is found exclusively in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. Collagen, in the form of elongated synthesis reactions that cause the most severe symptoms of scurvy Scurvy is a disease resulting from a deficiency of vitamin C, which is required for the synthesis of collagen in humans. The chemical name for vitamin C, ascorbic acid, is derived from the Latin name of scurvy, scorbutus, which also provides the adjective scorbutic . Scurvy leads to the formation of spots on the skin, spongy gums, and bleeding 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 Ascorbic acid is a sugar acid with antioxidant properties. Its appearance is white to light-yellow crystals or powder, and it is water-soluble. One form of ascorbic acid is commonly known as vitamin C. The name is derived from a- and scorbutus (scurvy), the disease caused by a deficiency of vitamin C. In 1937 the Nobel Prize for chemistry was) is required for a range of essential metabolic reactions Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular in all animals and plants. It is made internally Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step. Examples for such multi-step biosynthetic pathways are those for the by almost all organisms; notable mammalian group exceptions are most or all of the order chiroptera Bats are flying mammals in the order Chiroptera . The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than fly, and can only glide for short distances. Bats do (bats), and one of the two major primate A primate is a member of the biological order Primates (/praɪˈmeɪtiːz/ prī·mā′·tēz; Latin: "prime, first rank"), the group that contains prosimians (including lemurs, lorises, galagos and tarsiers ) and simians (monkeys and apes). With the exception of humans, who inhabit every continent on Earth,[a] most primates live in suborders, the Anthropoidea (Haplorrhini The haplorrhines, the "dry-nosed" primates , are members of the Haplorrhini clade: the prosimian tarsiers and all of the true simians. The simians are the catarrhines (Old World monkeys and apes, including humans) and the platyrrhines (New World monkeys)) (tarsiers, monkeys and apes, including human beings). Ascorbic acid is also not synthesized by guinea pigs, capybaras The capybara , also known as capibara, chigüire in Venezuela, Colombia, and Ecuador ronsoco in Peru, chigüiro, and carpincho in Spanish, and capivara in Portuguese, is the largest living rodent in the world. Its closest relatives are agouti, chinchillas, coyphillas, and guinea pigs. Its common name, derived from Kapiÿva in the Guarani language,, and some species of birds and fish. All species that do not synthesize ascorbate require it in the diet. Deficiency in this vitamin A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For causes the disease scurvy Scurvy is a disease resulting from a deficiency of vitamin C, which is required for the synthesis of collagen in humans. The chemical name for vitamin C, ascorbic acid, is derived from the Latin name of scurvy, scorbutus, which also provides the adjective scorbutic . Scurvy leads to the formation of spots on the skin, spongy gums, and bleeding in humans.^[3][4][5] It is also widely used as a food additive Food additives are substances added to food to preserve flavor or enhance its taste and appearance. Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines. With the advent of processed foods in the second half of the 20th century,.^[6]

Scurvy Scurvy is a disease resulting from a deficiency of vitamin C, which is required for the synthesis of collagen in humans. The chemical name for vitamin C, ascorbic acid, is derived from the Latin name of scurvy, scorbutus, which also provides the adjective scorbutic . Scurvy leads to the formation of spots on the skin, spongy gums, and bleeding 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 Reference Daily Intake (RDI) is the daily dietary intake level of a nutrient which was considered (at the time they were defined) to be sufficient to meet the requirements of nearly all (97–98%) healthy individuals in each life-stage and sex group. The RDI is used to determine the Daily Value which is printed on food labels in the U.S., Canada, ranging from 45 to 95 mg/day. Proponents of megadosage Vitamin C megadosage is the consumption of vitamin C in doses well beyond the current Dietary Reference Intake. This dose is similar to the consumption of ascorbate in other primates which, like humans, cannot synthesize their own vitamin C. Nearly all other animals synthesize vitamin C internally and as such, their cellular vitamin C 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 The common cold (viral upper respiratory tract infection , acute viral rhinopharyngitis, acute coryza, or cold) is a contagious, viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a sore throat, runny nose, and fever. There is no cure; however, symptoms usually 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]

Biological significance

Vitamin C is purely the L-enantiomer In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are "non-superposable" , much as one's left and right hands are "the same" but opposite. The term, pronounced /ɨˈnæntɪ.ɵmər/, is derived from the Greek 'ἐνάντιος', opposite, and 'μέρος', part or portion of ascorbate; the opposite D-enantiomer In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are "non-superposable" , much as one's left and right hands are "the same" but opposite. The term, pronounced /ɨˈnæntɪ.ɵmər/, is derived from the Greek 'ἐνάντιος', opposite, and 'μέρος', part or portion has no physiological significance. Both forms are mirror images A chiral molecule is a type of molecule that lacks an internal plane of symmetry and has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom of the same molecular structure. When L-ascorbate, which is a strong reducing agent A reducing agent is the element or compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox. For example consider the following reaction:, carries out its reducing Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the function, it is converted to its oxidized Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the form, L-dehydroascorbate Dehydroascorbic acid is an oxidized form of ascorbic acid. It is actively imported into the endoplasmic reticulum of cells and generates the oxidative potential found there. Protein disulfide isomerases are known to reduce DHA back to ascorbic acid, oxidizing their disulfide bonds in the process. Therefore L-dehydroascorbic acid is a vitamin C.^[2] L-dehydroascorbate can then be reduced back to the active L-ascorbate form in the body by enzymes Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their and glutathione Glutathione is a tripeptide. It contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side chain. Glutathione, an antioxidant, helps protect cells from reactive oxygen species such as free radicals and peroxides.^[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.

L-Ascorbate is a weak A weak acid is an acid that dissociates incompletely. It does not release all of its hydrogens in a solution, donating only a partial amount of its protons to the solution. These acids have higher pKa than strong acids, which release all of their hydrogen atoms when dissolved in water sugar acid structurally related to glucose Glucose , a simple sugar (monosaccharide), is an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name "glucose" comes that naturally occurs attached either to a hydrogen ion Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes. Depending on the charge of the ion, two different classes can be distinguished:, forming ascorbic acid Ascorbic acid is a sugar acid with antioxidant properties. Its appearance is white to light-yellow crystals or powder, and it is water-soluble. One form of ascorbic acid is commonly known as vitamin C. The name is derived from a- and scorbutus (scurvy), the disease caused by a deficiency of vitamin C. In 1937 the Nobel Prize for chemistry was, or to a metal ion A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by, forming a mineral ascorbate.

Biosynthesis and species-specific synthetic ability

The vast majority of animals and plants are able to synthesize their own vitamin C, through a sequence of four enzyme Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their-driven steps, which convert glucose Glucose , a simple sugar (monosaccharide), is an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name "glucose" comes to vitamin C.^[2] The glucose needed to produce ascorbate in the liver (in mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not and perching birds A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: it is roughly twice as diverse as the largest of the mammal orders, the Rodentia) is extracted from glycogen Glycogen is the molecule that functions as the secondary long-term energy storage in animal and fungi cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach. Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal; ascorbate synthesis is a glycogenolysis-dependent process.^[14] In reptiles Reptiles are animals in the class Reptilia. They are characterized by breathing air, laying tough-shelled amniotic eggs, and having skin covered in scales and/or scutes. Reptiles are classically viewed as having a "cold-blooded" metabolism. They are tetrapods (either having four limbs or being descended from four-limbed ancestors) and birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich the biosynthesis is carried out in the kidneys The kidneys are paired organs with several functions. They are seen in many types of animals, including vertebrates and some invertebrates. They are an essential part of the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid-base balance, and regulation of blood pressure. They serve the.

Among the animals that have lost the ability to synthesise vitamin C are simians and tarsiers, which together make up one of two major primate suborders, the anthropoidea, also called haplorrhini. This group includes humans. The other more primitive primates (strepsirrhini) retained the ability to make vitamin C, so this loss probably occurred in a common ancestor of the haplorrhini. Synthetic ability has been lost in a number of species (perhaps all species) in the small rodent family caviidae that includes guinea pigs and capybaras, but lost in other rodents (rats and mice do not need vitamin C, for example). A number of species of passerine birds also lost the ability, but not all of them, and those that have lost it are not clearly related; there is some evidence that the ability was lost separately a number of times in birds. All tested families of bats, including major insect and fruit-eating bat families have lost the ability to make vitamin C, and this loss may derive from a common bat ancestor, as a single mutation.

These animals all lack the L-gulonolactone oxidase (GULO) enzyme, which is required in the last step of vitamin C synthesis, because they have a defective form of the gene for the enzyme (Pseudogene ΨGULO).^[15] Some of these species (including humans) are able to make do with the lower levels available from their diets by recycling oxidised vitamin C.^[16]

Most simians consume the vitamin in amounts 10 to 20 times higher than that recommended by governments for humans.^[17] This discrepancy constitutes much of the basis of the controversy on current recommended dietary allowances. It is countered by arguments that humans are very good at conserving dietary vitamin C, and are able to maintain blood levels of vitamin C comparable with other simians, on a far smaller dietary intake.

An adult goat, a typical example of a vitamin C-producing animal, will manufacture more than 13 g of vitamin C per day in normal health and the biosynthesis will increase "manyfold under stress".^[18] Trauma or injury has also been demonstrated to use up large quantities of vitamin C in humans.^[19] Some microorganisms such as the yeast Saccharomyces cerevisiae have been shown to be able to synthesize vitamin C from simple sugars.^[20][21]

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