Vitamins are organic
molecules (or a set of closely related
molecules called vitamers)
that are essential to an organism in
small quantities for proper metabolic function. Essential
nutrients cannot be synthesized in
the organism in sufficient quantities for
survival, and therefore must be obtained through
the diet.
For example, vitamin
C can be synthesized by some species but not
by others; it is not considered a vitamin in the
first instance but is in the second. Most
vitamins are not single molecules, but groups of
related molecules called vitamers. For example,
there are eight vitamers of vitamin
E: four tocopherols and
four tocotrienols.
The term vitamin does
not include the three other groups of essential
nutrients: minerals, essential
fatty acids, and essential
amino acids.[2]
Major health
organizations list thirteen vitamins:[3][4][5]
Some sources
include a fourteenth, choline.[6]
Vitamins have
diverse biochemical functions. Vitamin A acts as
a regulator of cell and tissue growth and
differentiation. Vitamin D provides a
hormone-like function, regulating mineral
metabolism for bones and other organs. The B
complex vitamins function as enzyme cofactors (coenzymes)
or the precursors for
them. Vitamins C and E function as antioxidants.[7] Both
deficient and excess intake of a vitamin can
potentially cause clinically significant
illness, although excess intake of water-soluble
vitamins is less likely to do so.
All the vitamins
were discovered between 1913 and 1948.
Historically, when intake of vitamins from diet
was lacking, the results were vitamin deficiency
diseases. Then, starting in 1935, commercially
produced tablets of yeast-extract vitamin B
complex and semi-synthetic vitamin C became
available.[8] This
was followed in the 1950s by the mass production
and marketing of vitamin
supplements, including multivitamins,
to prevent vitamin deficiencies in the general
population.[8] Governments
have mandated the addition of some vitamins to staple
foods such as flour or milk, referred to as food
fortification, to prevent deficiencies.[9] Recommendations
for folic acid supplementation during pregnancy reduced
risk of infant neural
tube defects.[10]
