The common feature of free radicals is that their
molecular structure contains and unpaired electron.
Free radical molecules with an unpaired electron are
unstable and have a strong tendency to react with
other molecules by ‘‘stealing’’ an electron from them
to form a more stable electron pair. This reaction is
called oxidation (even when it happens with molecules
other than oxygen). In the body, free radicals cause
damage when they react with deoxyribonucleic acid
(DNA—genetic material), proteins, and lipids (fats).
Antioxidants are molecules that react with free radi-
cals in ways that neutralize them so they no longer are
able to ‘‘steal’’ electrons and cause damage.
Some important human antioxidants must be
acquired through diet, while others can be made by
the body.Vitamin C(ascorbic acid),vitamin E(alpha-
tocopherol),vitamin A(retinol), and beta-carotene are
the most important antioxidants the body must obtain
from food sources. Flavonoids found in tea, chocolate,
grapes, berries, onions, and wine also appear to have
antioxidant activity, although their role in health is
unclear. Selenium is sometimes classified as an antiox-
idant, although strictly, it is not. Selenium is a mineral
that must be acquired through diet. Plants grown in
geographic locations with selenium rich soil provide a
rich source of this mineral. Brazil nuts and tuna also
have high levels of selenium. It is a necessary part of
enzymes involved in antioxidant reactions. Glutathione
and coenzyme Q (ubiquinone) are the most important
antioxidants the body can make for itself.
Antioxidants and health
When free radicals build up faster than antioxidants
can neutralize them, the body develops a condition
called oxidative stress. Oxidative stress reduces the
body’s ability to deal with damage to cells and is
thought to play a role in the development of chronic
diseases such as cardiovascular disease, cancer, and
Alzheimer’s disease. Researchers know that a diet
high in fruits and vegetables containing antioxidants
promotes health and decreases the risk of developing
some chronic diseases such as atherosclerosis (harden-
ing of the arteries). In the early 2000s,dietary supple-
mentscontaining antioxidants were popularized as a
way to reduce oxidative stress, prevent health prob-
lems such as cancer, stroke, heart attack, and demen-
tia, and live longer. Research has since shown that
although there are relationships between antioxidant
levels and health, antioxidant dietary supplements are
not magic bullets to prevent age-related diseases.
One problem in determining whether there is a
cause and effect relationship between oxidative stress
and disease is that often it is not possible to tell if
oxidative stress causes a disease or if the disease brings
about oxidative stress as a result of biochemical
changes in diseased cells. Also, everyone develops oxi-
dative stress as they age, but not everyone develops the
same diseases. The interactions between an individu-
al’s diet, environment, genetic make-up, and health
are complex and still not well understood. Antioxi-
dants remain of great interest to researchers seeking
ways to prevent and cure chronic disease. Many clin-
ical trials are underway to determine safety and effec-
tiveness of different antioxidants, both alone and in
combination with other drugs and supplements.
CARDIOVASCULAR DISEASE.The strongest link
between antioxidant levels and health is related to the
development of cardiovascular disease. Low-densityHealth benefits of antioxidants and their food sourcesSeleniumBeta-caroteneVitamin EVitamin CHelps maintain healthy hair and nails, enhances immunity,
works with vitamin E to protect cells from damage. Reduces the
risk of cancer, particularly lung, prostate, and colorectal.
Keeps skin healthy, helps prevent night blindness and infections,
promotes growth and bone development.Acts as the protector of essential fats in cell membranes and red
blood cells. Reduces risk of cancer, heart disease, and other
age-associated diseases.
Destroys free radicals inside and outside cells. Helps in the
formation of connective tissue, the healing of wounds, and iron
absorption, and also helps to prevent bruising and keep gums
healthy. May reduce risk of cataracts, heart disease, and cancer.Garlic, seeds, Brazil nuts, meat, eggs, poultry, seafood, whole
grains. The amount in plant sources varies according to the
content of the soil.
Red, yellow-orange, and leafy green vegetables and fruits,
including carrots, apricots, cantaloupe, peppers, tomatoes,
spinach, broccoli, sweet potatoes, and pumpkin.
Peanut butter, nuts, seeds, vegetable oils and margarine, wheat
germ, avocado, whole grains, salad dressings.Peppers, tomatoes, citrus fruits and juices, berries, broccoli,
spinach, cabbage, potatoes, mango, papaya.Antioxidant Health benefits Food sourcesSOURCE: The American Dietetic Association(Illustration by GGS Information Services/Thomson Gale.)
Antioxidants