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Vitamins are classified according to their biological and chemical
activity, but not to their structure. Vitamins have diverse biochemical
functions. Some have hormone-like functions as regulators of mineral
metabolism (e.g., vitamin D), or regulators of cell and tissue growth
and differentiation (e.g., some forms of vitamin A). Others function as
antioxidants (e.g., vitamin E and sometimes vitamin C). The largest
number of vitamins (e.g., B complex vitamins) function as precursors
for enzyme cofactors, that help enzymes in their work as catalysts in
metabolism. Vitamins 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 carries various forms of carbon group–methyl, formyl, and
methylene– in the cell. Although these roles in assisting enzyme-
substrate reactions are vitamins’ best-known function, the other
vitamin functions are equally important.
The term vitamin was derived from “vitamine”, a combination
word made up by Polish scientist Casimir Funk from vital and amine,
meaning amine of life, because it was suggested in 1912 that the
organic micronutrient food factors that prevent beriberi and perhaps
other similar dietary-deficiency diseases might be chemical amines.
This proved incorrect for the micronutrient class, and the word was
shortened to vitamin.
Vitamins are classified as either water-soluble or fat-soluble.
There are 13 vitamins in humans: 4 fat-soluble (A, D, E and K) and 9
water-soluble (8 B vitamins and vitamin C). Water-soluble vitamins
are dissolved easily in water and, in general, are readily excreted from
the body. Fat-soluble vitamins are absorbed through the intestinal tract
with the help of lipids (fats).
Vitamins are essential for the normal growth and development of
a multicellular organism. Humans must consume vitamins periodically
but with differing schedules, to avoid deficiency. Being overdosed,
some vitamins cause side-effects such as nausea, diarrhea, and
vomiting.