A vitamin is an organic compound required as a nutrient in tiny amounts by an organism.[1] In other words, an organic chemical compound (or related set of compounds) 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 example, ascorbic acid (vitamin C) is a vitamin for humans, but not for most other animals, and biotin and vitamin D are required in the human diet only in certain circumstances. By convention, the term vitamin does not include other essential nutrients such as dietary minerals , essential fatty acids or essential amino acids (which are needed in larger amounts than vitamins), nor does it encompass the large number of other nutrients that promote health, but are otherwise required less often.[2] Thirteen vitamins are presently universally recognized.

Vitamins are classified by their biological and chemical activity, not their structure. Thus, each “vitamin” refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals are grouped under an alphabetized vitamin “generic descriptor” title, such as “vitamin A“, which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter-convertible to one another, as well.



In 1749, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease in which collagen is not properly formed, causing poor wound healing, bleeding of the gums, severe pain, and death.[5] In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the British Royal Navy. This led to the nickname Limey for sailors of that organization. Lind’s discovery, however, was not widely accepted by individuals in the Royal Navy’s Arctic expeditions in the 19th century, where it was widely believed that scurvy could be prevented by practicing good hygiene, regular exercise, and by maintaining the morale of the crew while on board, rather than by a diet of fresh food.[5] As a result, Arctic expeditions continued to be plagued by scurvy and other deficiency diseases. In the early 20th century, when Robert Falcon Scott made his two expeditions to the Antarctic, the prevailing medical theory was that scurvy was caused by “tainted” canned food.[5]

During the late 18th and early 19th centuries, the use of deprivation studies allowed scientists to isolate and identify a number of vitamins. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called “antirachitic A”. Thus, the first “vitamin” bioactivity ever isolated, which cured rickets, was initially called “vitamin A”, although confusingly the bioactivity of this compound is now called vitamin D.[7] In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu in present-day Estonia.[8] He fed mice an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. The mice that received only the individual constituents died, while the mice fed by milk itself developed normally. He made a conclusion that “a natural food such as milk must therefore contain, besides these known principal ingredients, small quantities of unknown substances essential to life.”[8] However, his conclusions were rejected by other researchers when they were unable to reproduce his results. One difference was that he had used table sugar (sucrose), while other researchers had used milk sugar (lactose) that still contained small amounts of vitamin B.




















There’re 13 vitamins that can we find in nature.


Table. Kinds of vitamins and time be discovered



Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is absolutely necessary for both scotopic and color vision. Vitamin A also functions in a very different role, as an irreversibly oxidized form of retinol known as retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.

Vitamin A can be found in two principal forms in foods:

  • retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester. It is also commercially produced and administered as esters such as retinyl acetate or palmitate.
  • The carotenes alpha-carotene, beta-carotene, gamma-carotene; and the xanthophyll beta-cryptoxanthin (all of which contain beta-ionone rings), but no other carotenoids, function as vitamin A in herbivores and omnivore animals, which possess the enzyme required to convert these compounds to retinal. In general, carnivores are poor converters of ionine-containg carotenoids, and pure carnivores such as cats and ferrets lack beta-carotene 15,15′-monooxygenase and cannot convert any carotenoids to retinal (resulting in none of the carotenoids being forms of vitamin A for these species).


retinol structure



Thiamine or thiamin or vitamin B1 (pronounced /ˈθaɪ.əmɨn/ THYE-ə-min), and named as the “thio-vitamine” (“sulfur-containing vitamin”) is a water-soluble vitamin of the B complex. First named aneurin for the detrimental neurological effects of its lack in the diet, it was eventually assigned the generic descriptor name vitamin B1. Its phosphate derivatives are involved in many cellular processes. The best-characterized form is thiamine pyrophosphate (TPP), a coenzyme in the catabolism of sugars and amino acids. In yeast, TPP is also required in the first step of alcoholic fermentation.

All living organisms use thiamine in their biochemistry, but it is synthesized in bacteria, fungi, and plants. Animals must obtain it from their diet, and, thus, for them it is a vitamin. Insufficient intake in birds produces a characteristic polyneuritis, and in mammals results in a disease called beriberi affecting the peripheral nervous system (polyneuritis) and/or the cardiovascular system, with fatal outcome if not cured by thiamine administration.[1] In less severe deficiency, nonspecific signs include malaise, weight loss, irritability and confusion.[2]

There is still much work devoted to elucidating the exact mechanisms by which thiamine deficiency leads to the specific symptoms observed (see below). New thiamine phosphate derivatives have recently been discovered,[3] emphasizing the complexity of thiamine metabolism and the need for more research in the field.

Thiamine structure



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.

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.[12] 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.[13] The presence of glutathione is crucial since it spares ascorbate and improves antioxidant capacity of blood.[14] Without it dehydroxyascorbate could not convert back to ascorbate.


Ascorbic acid structure



Vitamin D is a group of fat-soluble secosteroids, the two major physiologically relevant forms of which are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D without a subscript refers to either D2 or D3 or both. Vitamin D3 is produced in the skin of vertebrates after exposure to ultraviolet B light from the sun or artificial sources, and occurs naturally in a small range of foods. In some countries, staple foods such as milk, flour and margarine are artificially fortified with vitamin D, and it is also available as a supplement in pill form.[2] Food sources such as fatty fish, eggs, and meat are rich in vitamin D and are often recommended for consumption to those suffering vitamin D deficiency.[3]

Several forms (vitamers) of vitamin D have been discovered (see table). The two major forms are vitamin D2 or ergocalciferol, and vitamin D3 or cholecalciferol. These are known collectively as calciferol.[6] Vitamin D2 was chemically characterized in 1932. In 1936 the chemical structure of vitamin D3 was established and resulted from the ultraviolet irradiation of 7-dehydrocholesterol.[7]

Chemically, the various forms of vitamin D are secosteroids; i.e., steroids in which one of the bonds in the steroid rings is broken.[8] The structural difference between vitamin D2 and vitamin D3 is in their side chains. The side chain of D2 contains a double bond between carbons 22 and 23, and a methyl group on carbon 24.

Vitamin D2 (made from ergosterol) is produced by invertebrates, fungus and plants in response to UV irradiation; it is not produced by vertebrates.[9] Little is known about the biologic function of vitamin D2 in nonvertebrate species. Because ergosterol can more efficiently absorb the ultraviolet radiation that can damage DNA, RNA and protein it has been suggested that ergosterol serves as a sunscreening system that protects organisms from damaging high energy ultraviolet radiation.


Vitamin D5 structure



Riboflavin (E101 food color[1]), also known as vitamin B2, is an easily absorbed micronutrient with a key role in maintaining health in humans and animals. It is the central component of the cofactors FAD and FMN, and is therefore required by all flavoproteins. As such, vitamin B2 is required for a wide variety of cellular processes. It plays a key role in energy metabolism, and for the metabolism of fats, ketone bodies, carbohydrates, and proteins.

Milk, cheese, leafy green vegetables, liver, kidneys, legumes, tomatoes, yeast, mushrooms, and almonds[2] are good sources of vitamin B2, but exposure to light destroys riboflavin.

The name “riboflavin” comes from “ribose” (the sugar which forms part of its structure, which in turn is a transposition of arabinose[3]) and “flavin“, the ring-moiety which imparts the yellow color to the oxidized molecule (from Latin flavus, “yellow”). The reduced form, which occurs in metabolism, is colorless.

Riboflavin is best known visually as the vitamin which imparts the orange color to solid B-vitamin preparations, the yellow color to vitamin supplement solutions, and the unusual fluorescent yellow color to the urine of persons who supplement with high-dose B-complex preparations (no other vitamin imparts any color to urine).


Riboflavin structure


Vitamin E is a generic term for tocopherols and tocotrienols.[1] Vitamin E is a family of α-, β-, γ-, and δ- (respectively: alpha, beta, gamma, and delta) tocopherols and corresponding four tocotrienols. Vitamin E is a fat-soluble antioxidant that stops the production of reactive oxygen species formed when fat undergoes oxidation.[2][3][4] Of these, α-tocopherol (also written as alpha-tocopherol) has been most studied as it has the highest bioavailability.[5]


It has been claimed that α-tocopherol is the most important lipid-soluble antioxidant, and that it protects cell membranes from oxidation by reacting with lipid radicals produced in the lipid peroxidation chain reaction.[3][6] This would remove the free radical intermediates and prevent the oxidation reaction from continuing. The oxidised α-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol or ubiquinol.[7] However, the importance of the antioxidant properties of this molecule at the concentrations present in the body are not clear and it is possible that the reason why vitamin E is required in the diet is unrelated to its ability to act as an antioxidant.[8] Other forms of vitamin E have their own unique properties. For example, γ-tocopherol (also written as gamma-tocopherol) is a nucleophile that can react with electrophilic mutagens.[5]

However, the roles and importance of all of the various forms of vitamin E are presently unclear,[9][10] and it has even been suggested that the most important function of vitamin E is as a signaling molecule, and that it has no significant role in antioxidant metabolism.[11][12]

So far, most studies about vitamin E have supplemented using only alpha-tocopherol, but doing so leads to reduced serum gamma- and delta-tocopherol concentrations. Moreover, a 2007 clinical study involving alpha-tocopherol concluded that supplementation did not reduce the risk of major cardiovascular events in middle aged and older men.[13] For more information, read article tocopherol.


Tocopherol structure



Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid synthesis and energy production. As the largest and most structurally complicated vitamin, it can be produced industrially only through bacterial fermentation-synthesis.

Vitamin B12 consists of a class of chemically-related compounds (vitamers), all of which have vitamin activity. It contains the biochemically rare element cobalt. Biosynthesis of the basic structure of the vitamin in nature is only accomplished by simple organisms such as some bacteria and algae, but conversion between different forms of the vitamin can be accomplished in the human body. A common synthetic form of the vitamin, cyanocobalamin, does not occur in nature, but is used in many pharmaceuticals and supplements, and as a food additive, because of its stability and lower cost. In the body it is converted to the physiological forms, methylcobalamin and adenosylcobalamin, leaving behind the cyanide, albeit in minimal concentration. More recently, hydroxocobalamin (a form produced by bacteria), methylcobalamin, and adenosylcobalamin can also be found in more expensive pharmacological products and food supplements. The utility of these is presently debated.

Vitamin B12 was discovered from its relationship to the disease pernicious anemia, which is an autoimmune disease that destroys parietal cells in the stomach that secrete intrinsic factor. Intrinsic factor is crucial for the normal absorption of B12, so a lack of intrinsic factor, as seen in pernicious anemia, causes a vitamin B12 deficiency. Many other subtler kinds of vitamin B12 deficiency and their biochemical effects have since been elucidated.


Cobalamin structure



Vitamin K is a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation but also involved in metabolism pathways in bone and other tissue. They are 2-methyl1,4-naphthoquinone derivatives.

Vitamin K1 is also known as phylloquinone or phytomenadione (also called phytonadione). Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the large intestine,[1] and dietary deficiency is extremely rare unless the intestines are heavily damaged, are unable to absorb the molecule, or are subject to decreased production by normal flora, as seen in broad spectrum antibiotic use.[2]

There are three synthetic forms of vitamin K, vitamins K3, K4, and K5, which are used in many areas including the pet food industry (vitamin K3) and to inhibit fungal growth (vitamin K5).[3]

The function of vitamin K in the cell is to convert glutamate in proteins to gamma-carboxyglutamate (gla).





Pantothenic acid, also called pantothenate or vitamin B5 (a B vitamin), is a water-soluble vitamin. For many animals, pantothenic acid is an essential nutrient. Animals require pantothenic acid to synthesize coenzyme-A (CoA), and well as to synthesize and metabolize proteins, carbohydrates, and fats.

Pantothenic acid is the amide between pantoate and beta-alanine. Its name derives from the Greek pantothen (πάντοθεν) meaning “from everywhere” and small quantities of pantothenic acid are found in nearly every food, with high amounts in whole-grain cereals, legumes, eggs, meat, and royal jelly. It is commonly found as its alcohol analog, the provitamin panthenol, and as calcium pantothenate. Pantothenic acid is an ingredient in some hair and skin care products.

Pantothenic acid is used in the synthesis of coenzyme A (CoA). Coenzyme A may act as an acyl group carrier to form acetyl-CoA and other related compounds; this is a way to transport carbon atoms within the cell.[3] CoA is important in energy metabolism for pyruvate to enter the tricarboxylic acid cycle(TCA cycle) as acetyl-CoA, and for α-ketoglutarate to be transformed to succinyl-CoA in the cycle.[4] CoA is also important in the biosynthesis of many important compounds such as fatty acids, cholesterol, and acetylcholine.[4] CoA is incidentally also required in the formation of ACP[5], which is also required for fatty acid synthesis in addition to CoA.



Pantothenic acid structure





Biotin is a water-soluble B-complex vitamin (vitamin B7) that is composed of an ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a coenzyme in the metabolism of fatty acids and leucine, and it plays a role in gluconeogenesis.

Biotin D(+) is a cofactor responsible for carbon dioxide transfer in several carboxylase enzymes:

and, so, is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. Biotin covalently attaches to the epsilon-amino group of specific lysine residues in these carboxylases. This biotinylation reaction requires ATP and is catalyzed by holocarboxylase synthetase.[5] The attachment of biotin to various chemical sites can be used as an important laboratory technique to study various processes including protein localization, protein interactions, DNA transcription and replication. Biotinidase itself is known to be able to biotinylate histone proteins,[6] but little biotin is found naturally attached to chromatin.

Biotin binds very tightly to the tetrameric protein avidin (also streptavidin and neutravidin), with a dissociation constant Kd in the order of 10−15, which is one of the strongest known protein-ligand interactions, approaching the covalent bond in strength.[7] This is often used in different biotechnological applications. Until 2005, very harsh conditions were required to break the biotin-streptavidin bond.

Biotin structure


Vitamin B6 is a water-soluble vitamin and is part of the vitamin B complex group. Several forms of the vitamin are known, but pyridoxal phosphate (PLP) is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation. PLP also is necessary for the enzymatic reaction governing the release of glucose from glycogen.

Seven forms of this vitamin are known:

Pyridoxine structure



Niacin (also known as vitamin B3, nicotinic acid and vitamin PP) is an organic compound with the formula C6H5NO2 and, depending on the definition used, one of the forty to eighty essential human nutrients. This colorless, water-soluble solid is a derivative of pyridine, with a carboxyl group (COOH) at the 3-position. Other forms of vitamin B3 include the corresponding amide, nicotinamide (“niacinamide”), where the carboxyl group has been replaced by a carboxamide group (CONH2), as well as more complex amides and a variety of esters. The terms niacin, nicotinamide, and vitamin B3 are often used interchangeably to refer to any member of this family of compounds, since they have the same biochemical activity.

Niacin cannot be directly converted to nicotinamide, but both compounds could be converted to NAD and NADP in vivo. Although the two are identical in their vitamin activity, nicotinamide does not have the same pharmacological effects as niacin, which occur as side effects of niacin’s conversion. Nicotinamide does not reduce cholesterol or cause flushing.[1] Nicotinamide may be toxic to the liver at doses exceeding 3 g/day for adults.[2] Niacin is a precursor to NAD+/NADH and NADP+/NADPH, which play essential metabolic roles in living cells.[3] Niacin is involved in both DNA repair, and the production of steroid hormones in the adrenal gland.

Niacin is one of five vitamins associated with a pandemic deficiency disease:


Niacin structure


Folic acid (also known as vitamin B9[1] or folacin) and folate (the naturally occurring form), as well as pteroyl-L-glutamic acid and pteroyl-L-glutamate, are forms of the water-soluble vitamin B9. Folic acid is itself not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion to dihydrofolic acid in the liver.[2]

Vitamin B9 (folic acid and folate inclusive) is essential to numerous bodily functions ranging from nucleotide biosynthesis to the remethylation of homocysteine. The human body needs folate to synthesize DNA, repair DNA, and methylate DNA as well as to act as a cofactor in biological reactions involving folate.[3] It is especially important during periods of rapid cell division and growth. Children and adults both require folic acid in order to produce healthy red blood cells and prevent anemia.[4] Folate and folic acid derive their names from the Latin word folium (which means “leaf”). Leafy vegetables are a principal source, although, in Western diets, fortified cereals and bread may be a larger dietary source.


Folic acid structure



A vitamin is an organic compound required as a nutrient in tiny amounts by an organism.

Vitamins are classified by their biological and chemical activity, not their structure.

Vitamins are very important for our body. There’re 13 vitamins that can we find in nature.

1.      Vitamin A (retinol)

2.      Vitamin B1 (thiamine)

3.      Vitamin C (ascorbic acid)

4.      Vitamin D (calciferol)

5.      Vitamin B2 (riboflavin)

6.      Vitamin E (tocopherol)

7.      Vitamin B12 (cobalamin)

8.      Vitamin K

9.      Vitamin B5 (pantothenic acid)

10.  Vitamin B7 (biotin)

11.  Vitamin B6 (pyridoxine)

12.  Vitamin B3 (niacin)

13.  Vitamin B9 (folic acid)






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