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|Section2= |Section6= |Section7= }} Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals. When converted to the retinal (retinaldehyde) form, vitamin A is essential for vision, and when converted to retinoic acid is essential for skin health, teeth remineralization and bone growth. These chemical compounds are collectively known as retinoids, and possess the structural motif of all-''trans'' retinol as a common feature in their structure. Structurally, all retinoids also possess a β-ionone ring and a polyunsaturated side chain, with either an alcohol, aldehyde, a carboxylic acid group or an ester group. The side chain is composed of four isoprenoid units, with a series of conjugated double bonds which may exist in ''trans''- or ''cis''-configuration.〔 Retinol is produced in the body from the hydrolysis of retinyl esters, and from the reduction of retinal. Retinol in turn is ingested in a precursor form; animal sources (liver and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain provitamin A carotenoids (these may also be considered simply vitamin A). Hydrolysis of retinyl esters results in retinol, while provitamin A carotenoids can be cleaved to produce retinal by carotene dioxygenase in the intestinal mucosa. Retinal, also known as retinaldehyde, can be reversibly reduced to produce retinol or it can be ''irreversibly'' oxidized to produce retinoic acid, which then cannot function as the vitamin in the eye. Commercial production of retinol typically requires retinal synthesis through reduction of a pentadiene derivative and subsequent acidification/hydrolysis of the resulting isomer to produce retinol. Pure retinol is extremely sensitive to oxidization and is prepared and transported at low temperatures and oxygen free atmospheres. When prepared as a dietary supplement, retinol is stabilized as the ester derivatives retinyl acetate or retinyl palmitate. ==Discovery== In 1913, Elmer McCollum, a biochemist at the University of Wisconsin–Madison, and colleague Marguerite Davis identified a fat-soluble nutrient in butterfat and cod liver oil. Their work confirmed that of Thomas Osborne and Lafayette Mendel, at Yale, which suggested a fat-soluble nutrient in butterfat, also in 1913. Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens. Although the vitamin A was not identified until the 20th century, written observations of conditions created by deficiency of this nutrient appeared much earlier in history. Sommer (2008) classified historical accounts related to vitamin A and/or manifestations of deficiency as follows: "Ancient" accounts; 18th- to 19th-century clinical descriptions (and their purported etiologic associations); early 20th-century laboratory animal experiments, and clinical and epidiomologic observations that identified the existence of this unique nutrient and manifestations of its deficiency.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「retinol」の詳細全文を読む スポンサード リンク
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