:: Vitamins and Minerals
How Vitamins Work
In the body, proteins, carbohydrates, and fats
combine with other substances to yield energy
and build tissues. These chemical reactions are
catalyzed, or accelerated, by enzymes produced
from specific vitamins, and they take place in
specific parts of the body.
The vitamins needed by humans are divided into
two categories: water-soluble vitamins (the B
vitamins and vitamin C)
and fat-soluble vitamins (A,
and K). The water-soluble vitamins are absorbed
by the intestine and carried by the circulatory
system to the specific tissues where they will
be put into use. The B vitamins act as coenzymes,
compounds that unite with a protein component
called an apoenzyme to form an active enzyme.
The enzyme then acts as a catalyst in the chemical
reactions that transfer energy from the basic
food elements to the body. It is not known whether
vitamin C acts as a coenzyme.
a person takes in more water-soluble vitamins than are needed,
small amounts are stored in body tissue, but most of the excess
is excreted in urine. Because water-soluble vitamins are not
stored in the body in appreciable amounts, a daily supply
is essential to prevent depletion.
Fat-soluble vitamins seem to have highly specialized
functions. The intestine absorbs fat-soluble vitamins,
and the lymph system carries these vitamins to
the different parts of the body. Fat-soluble vitamins
are involved in maintaining the structure of cell
membranes. It is also believed that fat-soluble
vitamins are responsible for the synthesis of
The body can store larger amounts of fat-soluble
vitamins than of water-soluble vitamins. The liver
provides the chief storage tissue for vitamins
A and D, while vitamin E is stored in body fat
and to a lesser extent in reproductive organs.
Relatively little vitamin K is stored. Excessive
intake of fat-soluble vitamins, particularly vitamins
A and D, can lead to toxic levels in the body.
Many vitamins work together to regulate several
processes within the body. A lack of vitamins
or a diet that does not provide adequate amounts
of certain vitamins can upset the body's internal
balance or block one or more metabolic reactions.