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Vitamin

A '''vitamin''' is an organic compound required as a nutrient in tiny amounts by an organism.biosynthesis|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 functions as vitamin C for some animals but not others, and vitamin D|vitamins D and vitamin K|K are required in the human diet only in certain circumstances.vitamin - definition of vitamin by the Free Online Dictionary, Thesaurus and Encyclopedia Vitamins are classified by their biological and chemical activity, not their structure. Thus, each "vitamin" may refer to several ''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 many carotenoids. Vitamers are often inter-converted in the body. The term ''vitamin'' does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but are otherwise required less often. Vitamins have diverse biochemical functions, including function as hormones (e.g. vitamin D), antioxidants (e.g. vitamin E), and mediators of cell signaling and regulators of cell and tissue growth and differentiation (e.g. vitamin A).Accessed Jan 4, 2008 The largest number of vitamins (e.g. B complex vitamins) function as precursors for enzyme cofactor (biochemistry)|cofactor biomolecule|bio-molecules (coenzymes), that help act as catalysts and Substrate (chemistry)|substrates in metabolism. When acting as part of a catalyst, vitamins are bound to enzymes and are called prosthetic groups. For example, biotin is part of enzymes involved in making fatty acids. Vitamins also act as coenzymes to carry chemical groups between enzymes. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene - in the cell. Although these roles in assisting enzyme reactions are vitamins' best-known function, the other vitamin functions are equally important. Until the 1900s, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) can alter the types and amounts of vitamins ingested. Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades,Egyptians knew that feeding a patient liver would help cure night blindness, an illness now known to be caused by a vitamin A deficiency. The advancement of ocean voyage during the Renaissance resulted in prolonged periods without access to fresh fruits and vegetables, and made illnesses from vitamin deficiency common among ship's crew. In 1749, the Scotland|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 gingiva|gums, severe pain, and death.Jack Challem (1997). "The Past, Present and Future of Vitamins" 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. 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" canning|canned food. In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu in present-day Estonia.1929 Nobel lecture He fed mouse|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." 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.

References

General References Include:
- ''Stedman's Medical Dictionary''. Ed. Maureen Barlow Pugh et.al. 27th ed. Baltimore: Lippincott Williams & Wilkins, 2000.
- Donatelle, Rebecca J. ''Health: The Basics''. 6th ed. San Francisco: Pearson Education, Inc. 2005.

External links

- USDA RDA chart in PDF format
- Health Canada Dietary Reference Intakes Reference Chart for Vitamins
- NIH Office of Dietary Supplements: Fact Sheets
- NIH Office of Dietary Supplements. Dietary Supplements: Background Information Category:Essential nutrients Category:Nutrition Category:Vitamins|* zh-min-nan:Bî-tá-mín simple:Vitamin

Related Images

- Fruits and vegetables are often a good source of vitamins.

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