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Human vitamin A is derived from the natural food. Natural vitamin A exists in dif ferent forms. In animal tissues, vitamin A is present in the form of retinoids. However, in plants, the form of vitamin A called carotenoids is contained in the green, orange, and yellow plant tissue. Vitamin A compounds such as retinol, reti nal, carotene, and so on from these foods can be converted to vitamin A in the human body. Therefore, food is the main source of vitamin A.
As early as 1000 years ago, the Qian Jin Yao Fang written by Sun Simiao in Tang Dynasty recorded that animal liver can cure night blindness. This is the early recognition in vitamin A supplementation. The traditional Chinese medicine books also recorded that nourishing the liver can improve eyesight. Researches on the therapy of vitamin A deficient-diseases are mainly related to nourishing the liver and kidney, supplementing essence and blood, and activating qi

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Yellow-Orange Powder

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Vitamin A1 (VA1), Molecular formula, C20H30O; MW, 286.45; CAS, 68-26-8. Melting point: 62–64 °C. Boiling point: 137–138 °C
VA2, Molecular formula, C20H28O; MW, 284.44; Melting point: 17–19 °C.

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The vitamin research is the great achievement in the development of life sciences, while human beings only took half a century to discover and understand vitamins. However, everything is still very difficult for scientists in the early stage of vitamin discovery. From 1913 to 1915, Elmer McCollum and Marguerite Davis indicated that the growth rate was maintained by at least two different kinds of growth factors: one can be separated from eggs or butter, and the other one which multiple neuritis of chicks and pigeons can be extracted by water; thus they were named fat-soluble vitamin A and water-soluble vitamin B.prevented
In 1919, the researchers demonstrated that fat-soluble vitamin A not only sup ported the rate of growth but also prevented eye dryness and night blindness in the process of property study. In 1920, Dr. J.C. Drummond named this active lipid as vitamin A. It exists in cod liver oil and prevents the occurrence of eye dryness and night blindness.

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Occurs preformed only in animals; metabolized from carotenoids, such β-carotene, in the intestinal mucosa. Dietary sources include liver, milk, butter, cheese, eggs and fish liver oils or as carotenoi s from fruits and vegetables. Stored primarily in the liver in esterified form; transported in the blood by retinol binding protein (RBP). Nutritional factor.

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ChEBI: A retinol in which all four exocyclic double bonds have E- (trans-) geometry.

Indications

Vitamin A, or retinol, is essential for the proper maintenance of the functional and structural integrity of epithelial cells, and it plays a major role in epithelial differentiation. Bone development and growth in children have also been linked to adequate vitamin A intake. Vitamin A, when reduced to the aldehyde 11-cis-retinal, combines with opsin to produce the visual pigment rhodopsin. This pigment is present in the rods of the retina and is partly responsible for the process of dark adaptation.

World Health Organization (WHO)

Vitamin A, a fat-soluble vitamin, is used in the treatment and prevention of vitamin A deficiency resulting from inadequate dietary intake. It has been demonstrated to be teratogenic at high doses (more than 25,000 IU per day). Daily dosages of less than 10000 IU seem to be free of this risk. Retinol (vitamin A) is listed in the WHO Model List of Essential Drugs.

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Retinal, retinol and retinoic acid are the aldehyde, alcohol and acid forms of vitamin A. The retinoids exist as many geometric isomers due to the unsaturated bonds in the aliphatic chain. Retinol is biologically active in a wide range of processes.

Clinical Use

Principal dietary sources of vitamin A are milk fat (cheese and butter) and eggs. Since it is stored in the liver, inclusion of liver in the diet also provides vitamin A. A plant pigment, carotene, is a precursor for vitamin A and is present in highly pigmented vegetables, such as carrots, rutabaga, and red cabbage.
An early sign of hypovitaminosis A is night blindness. This condition is related to the role of vitamin A as the prosthetic group of the visual pigment rhodopsin. The night blindness may progress to xerophthalmia (dryness and ulceration of the cornea) and blindness. Other symptoms of vitamin A deficiency include cessation of growth and skin changes due to hyperkeratosis.
Since vitamin A is a fat-soluble vitamin, any disease that results in fat malabsorption and impaired liver storage brings with it the risk of vitamin A deficiency; these conditions include biliary tract disease, pancreatic disease, sprue, and hepatic cirrhosis. One group at great risk are children from low-income families, who are likely to lack fresh vegetables (carotene) and dairy products (vitamin A) in the diet.

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Acute hypervitaminosis A results in drowsiness, headache, vomiting, papilledema, and a bulging fontanel in infants. The symptoms of chronic toxicity include scaly skin, hair loss, brittle nails, and hepatosplenomegaly. Anorexia, irritability, and swelling of the bones have been seen in children. Retardation of growth also may occur. Liver toxicity has been associated with excessive vitamin A intake. Vitamin A is teratogenic in large amounts, and supplements should not be given during a normal pregnancy. The IOM has reported the UL of vitamin A to be 3,000 μg/day.

Safety Profile

Moderately toxic by ingestion. Human teratogenic effects by ingestion: developmental abnormalities of the craniofacial area and urogenital system. An experimental teratogen. Experimental reproductive effects. Human mutation data reported. When heated to decomposition it emits acrid smoke and irritating fumes.

Purification Methods

Purify retinol by chromatography on columns of water-deactivated alumina and elute with 3-5% acetone in hexane. Separate the isomers by TLC plates on silica gel G, developed with pet ether (low boiling)/methyl heptanone (11:2). Store it in the dark, under N2, at 0o, or in Et2O, Me2CO or EtOAc. [See Gunghaly et al. Arch Biochem Biophys 38 75 1952, Beilstein 6 IV 4133.]

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