lipoprotein cholesterol (LDL or ‘‘bad cholesterol’’)
appears to react with free radicals. This changes the
LDL cholesterol in a way that allows it to accumulate
in cells lining the blood vessels. These cholesterol-
loaded cells are precursors to the development of pla-
que, hard deposits that line blood vessels and cause
cardiovascular disease, heart attack, and stroke.
Researchers thought increasing the amount of
antioxidants in the blood by taking supplements
would decrease the number of free radicals available
to interact with LDL cholesterol and thus lower the
risk of developing cardiovascular disease. This theory
has not been proved. In fact, a paper published in the
Journal of the American Medical Associationon Feb-
ruary 28, 2007, analyzed 68 trials of antioxidant sup-
plements involving about 232,600 patients. The
authors concluded that antioxidant supplements did
not prolong life. In fact, when only rigorous, well-
controlled studies were analyzed, the risk of dying
increased 5%. This analysis is quite controversial,
with some experts questioning the analytical methods
used. However, the American Heart Association and
similar organizations in other countries advocate car-
diovascular disease prevention through consumption
of fruits, vegetables, whole grains and nuts high in
antioxidants and other heart-protecting nutrients
instead of antioxidant supplements.
CANCER.Free radicals damage DNA, and some-
times this damage leads to development of cancer. In
laboratory cell cultures and animal studies, antioxi-
dants appear to slow the development of cancer. The
results have been mixed in studies where humans took
antioxidant dietary supplements. A large study of
29,000 men showed that when a beta-carotene dietary
supplement was taken by men who smoked, they
developed lung cancer at a rate 18% higher and died
at a rate 8% higher than men who did not receive the
supplement. Another study that gave men dietary
supplements of beta-carotene and vitamin A was
stopped when researchers found the men receiving
the beta-carotene had a 46% greater chance of dying
from lung cancer than those who did not receive the
supplement. Other large studies have shown either no
or only slight protective effects against cancer. The
position of the American Cancer Society, the National
Cancer Institute, and several international health
organizations is that antioxidants should come from
a healthy diet high in fruits and vegetables and low in
fat and not from dietary supplements.
AGE-RELATED VISION IMPAIRMENT.Cataracts and
age-related macular degeneration are two types of
vision impairment common in older individuals. Cat-aracts develop because of changes in theproteinin the
lens of the eye. These changes cause the lens to become
cloudy and limit vision. The changes may be due to
damage by free radicals. Age-related macular degen-
eration is an irreversible disease of the retina that
causes blindness. Two carotenoid antioxidants, zeax-
anthin and lutein, are found in the retina and are
essential to vision. However, study participants who
took antioxidant supplements over several years did
not have a reduced risk of developing these diseases.PrecautionsThe mixed results obtained in human studies of
antioxidant supplements suggests that all antioxidants
should come from foods and not from dietaryKEY TERMS
Coenzyme—Also called a cofactor; a small non-
protein molecule that binds to an enzyme and cat-
alyzes (stimulates) enzyme-mediated reactions.
Dietary supplement—A product, such as a vitamin,
mineral, herb, amino acid, or enzyme, intended to
be consumed in addition to an individual’s diet
with the expectation that it will improve health.
Enzyme—A protein that changes the rate of a
chemical reaction within the body without them-
selves being used up in the reaction.
Free radical—A molecule with an unpaired elec-
tron that has a strong tendency to react with other
molecules in deoxyribonucleic acid (DNA), pro-
teins, and lipids (fats), resulting in damage to cells.
Free radicals are neutralized by antioxidants.
Mineral—An inorganic substance found in the
earth that is necessary in small quantities for the
body to maintain a health. Examples: zinc, copper,
iron.
Oxidation—Interaction in which one molecule
removes an electron from another molecule to sta-
bilize itself.
Retina—The layer of light-sensitive cells on the
back of the eyeball that function in converting
light into nerve impulses.
Vitamin—An essential nutrient the body needs in
small amounts to remain healthy but that the body
cannot manufacture for itself and must acquire
through diet.Antioxidants