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Vitamin World
A vitamin is an organic compound and a
vital nutrient that an organism requires in limited amounts. An organic chemical
compound (or related set of compounds) is called a vitamin when the organism
cannot synthesize the compound in sufficient quantities, and it must be
obtained through the diet; thus, the term "vitamin" is conditional
upon the circumstances and the particular organism. For example, ascorbic acid
(one form of vitamin C) is a vitamin for humans, but not for most other animal
organisms. Supplementation is important for the treatment of certain health
problems,[1] but there is little evidence of nutritional benefit when used by
otherwise healthy people.[2]
By convention the term vitamin includes
neither other essential nutrients, such as dietary minerals, essential fatty
acids, or essential amino acids (which are needed in greater amounts than
vitamins) nor the great number of other nutrients that promote health, and are
required less often to maintain the health of the organism.[3] Thirteen
vitamins are universally recognized at present. 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 is 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.
Vitamins have diverse biochemical
functions. Some, such as vitamin D, have hormone-like functions as regulators
of mineral metabolism, or regulators of cell and tissue growth and
differentiation (such as some forms of vitamin A). Others function as
antioxidants (e.g., vitamin E and sometimes vitamin C).[4] The largest number
of vitamins, the B complex vitamins, function as enzyme cofactors (coenzymes)
or the precursors for them; coenzymes help enzymes in their work as catalysts
in metabolism. In this role, vitamins may be tightly bound to enzymes as part
of prosthetic groups: For example, biotin is part of enzymes involved in making
fatty acids. They may also be less tightly bound to enzyme catalysts as
coenzymes, detachable molecules that function to carry chemical groups or
electrons between molecules. For example, folic acid may carry methyl, formyl,
and methylene groups in the cell. Although these roles in assisting
enzyme-substrate reactions are vitamins' best-known function, the other vitamin
functions are equally important.[5]
Until the mid-1930s, when the first
commercial yeast-extract vitamin B complex and semi-synthetic vitamin C
supplement tablets were sold, vitamins were obtained solely through food
intake, and changes in diet (which, for example, could occur during a
particular growing season) usually greatly altered the types and amounts of
vitamins ingested. However, vitamins have been produced as commodity chemicals
and made widely available as inexpensive semisynthetic and synthetic-source
multivitamin dietary and food supplements and additives, since the middle of
the 20th century. Study of structural activity, function and their role in
maintaining health is called vitaminology
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