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Understanding
Antioxidants
By
Ahmed H. Kissebah, M.D., Ph.D.
To understand
antioxidants, we have to first know what a
free radical is. In the body’s cells, oxygen
is utilized in a number of chemical
reactions to generate energy from nutrients
such as sugars, fats and protein components.
Oxygen is also utilized in the process of
storing any excess of these nutrients.
During these processes, the oxygen is
converted to a highly unstable form that has
the capacity to combine with other
components of the body’s cells. This
unstable form is known as a free radical.
When there is an excess of these unstable
forms, this can cause damage to cells within
vital organs. In addition to the normal
process of energy production and nutrient
storage, other environmental agents such as
exposure to ultraviolet light, air
pollution, excess heat and smoking can also
cause the generation of excess free
radicals.
Free
radicals seem to play a role in many chronic
diseases. It can cause the buildup of
plaques in the walls of blood vessels,
leading to “atherosclerosis,” with its
complications such as heart attacks and
strokes. It can also damage the basic
genetic material in our cells, known as
“DNA.” This damage is considered a factor in
the process that may lead to cancer. Free
radicals are also known to contribute to
body changes that accompany aging.
Free radicals, however,
are not always harmful. Certain immune
cells, for example, manufacture them and use
them as weapons against invading bacteria
and viruses. Free radicals may also react
with certain chemicals in the body known as
“prostaglandins,” which are involved in many
of the body’s reactions against inflammation
accompanying arthritis.
Antioxidants are chemicals
and/or systems that help to deactivate free
radicals. They are part of the body’s
defense systems against the accumulation of
those harmful radicals. They work primarily
by restoring the stable state of oxygen that
has been super-activated by the formation of
free radicals.
Some of these antioxidants
are vitamins, like vitamins C and E, or
minerals, like selenium. One of the
important classes of antioxidants is known
as the “carotenoids.” These antioxidants are
found in
vegetables, fruits and
grains and, to some extent, in chocolate,
tea and coffee. Most studies have failed to
show the benefit of one, single antioxidant
over another. We do know, however, that a
healthy diet rich in fruits, whole grains
and vegetables—in other words, a diet
containing the various types of
antioxidants—can help reduce the risk of
many diseases.
The combination of
antioxidants found in foods appears to be of
the most benefit. Although, at one time,
people were advised that the intake of
vitamin C and/or E are protective, recent
studies have cautioned about the excessive
use of those supplements. Indeed, the intake
of excess vitamin C may actually interfere
with the benefits of radiation and
chemotherapy treatment in patients with
cancer.
The main over-the-counter
(OTC) supplements marketed as antioxidants
include:
Vitamin E
Vitamin E is a fat-soluble vitamin present
in nuts, seeds, vegetables, fish oils,
apricots, fortified cereals, and whole
grains such as wheat germ. Vitamin E is the
principal antioxidant in the body and is a
strong free radical “quencher” or
“neutralizer.” It has, therefore, been
thought of as protective against DNA damage
and risks
of heart disease, stroke
and cancer. It is also protective against
cataracts, an eye condition that results in
cloudiness of vision, and in the prevention
of arthritis and some neurologic disorders.
Vitamin E has been reported to cause
improvement of the mental well-being in the
elderly. The recommended daily allowance of
vitamin E is 15 IU for men and 12 IU for
women.
Vitamin C
Vitamin C is a water-soluble
vitamin present in citrus fruits and juices,
green peppers, cabbage, spinach, broccoli,
cantaloupe, kiwi and strawberries. It
interacts strongly with free radicals
floating in the body fluids between cells.
As with vitamin E, vitamin C has protective
effects against cardiovascular disease,
cancer, cataracts and some neurological
disorders. The recommended daily allowance
is 60 mg for both men and women. Larger
quantities of vitamin C are thought to be
protective against systems of the common
cold. In men, supplementation with vitamin C
has also been shown to improve both the
quantity and quality of sperm count reduced
by cigarette smoking.
B-carotene
(beta-carotene)
Carotenoids are a group of red, orange and
yellow pigments found in plant foods,
particularly in fruits and vegetables.
B-carotene is one member
of that group and is converted by the body
to Vitamin A.
B-carotene is found
naturally in liver, egg yolk, milk, butter,
spinach, carrots, squash, broccoli, tomato,
cantaloupe, peaches and grains. It is one of
the most powerful free radical quenchers. It
has been shown to be protective against
cardiovascular disease and cancer.
Humans require external
sources of vitamin E, C and beta-carotene
because the body is unable to manufacture
them. Hence, efforts should be made to
ensure the optimal intake of foods rich in
these compounds. Indeed,
diets need to be improved,
with a greater emphasis placed on
consumption of antioxidant-rich vegetables
and fruits. At least five servings of fruits
and vegetables should be included in the
diet daily.
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