vitamin is an organic compound required as a nutrient in tiny
amounts by an organism. A compound 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 functions as vitamin C for some animals
but not others, and vitamins D and K are required in the human
diet only in certain circumstances.
are classified by their biological and chemical activity,
not their structure. Thus, each "vitamin" actually
refers to a number of vitamer compounds, which form a set
of distinct chemical compounds that show the biological activity
of a particular vitamin. Such a set of chemicals are grouped
under an alphabetized vitamin "generic descriptor"
title, such as "vitamin A," which (for example)
includes retinal, retinol, and many carotenoids. Vitamers
are often inter-convertible 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.
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). The largest
number of vitamins (e.g. B complex vitamins) function as precursors
for enzyme cofactor bio-molecules (coenzymes), that help act
as catalysts and 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.
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, allowing supplementation of the dietary intake.
food supplement is, typically, a nutrient added to a foodstuff
which would otherwise not contain that nutrient. In general,
the term is restricted to those additives which are deemed
to be positive for health, growth or well-being.
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