The Importance of Antioxidants in Life

ABSTRACT

Antioxidants are believed to help alleviate many
diseases, from cancer to heart problems. All
antioxidants, however, are not created equal and
the consumer should understand what these
compounds are and what they are capable of
doing. Research suggests that certain
antioxidants can indeed be helpful.

It's hard to open a magazine about health and
nutrition without seeing the word "antioxidants"
peppered throughout the articles and ads. People
read grandiose claims that these substances can
prevent cancer, heart disease, Alzheimer's,
Parkinson's, diabetes, and cataracts, not to
mention increase longevity and give their skin a
youthful glow. Millions of Americans take
supplements containing one or more antioxidants
every day, sometimes on their doctor's advice.

Yet many individuals are confused. They may buy
products that contain antioxidants without fully
understanding what these compounds are and what
they can and cannot do. Vitamins C and E,
beta-carotene and other carotenoids (chemicals
that give plants their red, orange, or yellow
color), and the mineral selenium are the
most-studied antioxidants. Although the
nutrients act on cells in similar ways, they are
not interchangeable or uniformly beneficial. In
fact, they differ from one another considerably,
and researchers are just beginning to understand
the particular role each one may play in warding
off disease. Vitamin E, for example, appears to
help prevent heart disease, while the
carotenoids may protect the retina of the eye
against degeneration.

Their Common Enemy

All cells in the human body use oxygen to break
down the carbohydrates, fats, and proteins that
give them energy. Just as a car creates exhaust
as it burns fuel, metabolically active cells
produce byproducts called free radicals. These
are oxygen molecules that have lost one electron
(a negatively charged particle) and seek to
stabilize themselves by stealing an electron
from a nearby molecule.

Free radicals are not choosy about where they
get their electrons, and they will readily
attach to -- and damage -- proteins, fats, and
other chemicals in the body. When free radicals
attack DNA, a cell's genetic material, they may
induce the cell to undergo changes that lead to
uncontrolled cell proliferation -- which is
cancer.

Fortunately, cells come equipped with a defense
system for combating free radicals; they
naturally produce a variety of antioxidants,
chemicals that limit the activity of free
radicals and repair their damage. However, some
researchers believe that, as people age, their
cells generate fewer of these protective
compounds, or the ones they produce become less
efficient at doing their job. Theoretically, an
age-related increase in uncontrolled free
radicals may explain why many diseases become
more common as people grow older.

It's no wonder, then, that antioxidants have
generated so much publicity. The following is a
summary of the published research on antioxidant
nutrients to help people separate fact from hype.

Heart Disease

Researchers suspect that free radicals may
promote some cases of heart disease. When these
molecules damage low-density lipoprotein (LDL)
cholesterol inside blood vessels, white blood
cells flock to the site and consume the LDL in
an attempt to repair the injury. White cells
swollen with LDL particles become foam cells;
these lipid-laden cells are thought to be the
beginning of atherosclerotic plaques in the
arteries.

A consistent body of research indicates that
vitamin E may protect people against heart
disease, possibly by preventing free radicals
from damaging LDL particles. The bulk of the
evidence is from observational investigations --
that is, studies in which the participants
reported their intake of E on questionnaires.
They were not asked to take the vitamin as part
of a clinical trial.

Because the amount of E thought to provide
cardiac benefit could not be obtained solely
from dietary sources (which include vegetable
oils, nuts, and whole grains), most studies have
focused on individuals who get their E through
supplements. The data generally indicate that
taking doses ranging from 100 to 800 IU
(International Units) per day may lower the risk
of heart disease by 30%-40%.

Americans typically get about 17 IU of vitamin E
a day through diet; the current Reference Daily
Intake (RDI) is 30 IU. However, some doctors now
recommend that their patients -- both healthy
individuals and those with coronary artery
disease -- take E supplements containing higher
doses to prevent or slow heart disease.

Neither the American Heart Association nor
professional medical societies endorse E
supplements, though, mainly because most of the
published research is observational. To date,
there have only been two controlled clinical
trials evaluating E.

In a Finnish trial of nearly 30,000 male smokers
tracked for 5-8 years, the supplements did not
appear to reduce the risk of heart disease
compared to a placebo, but the dose of E was
relatively small -- about 50 IU daily. By
contrast, a British study that compared the
effects of high doses, 400 or 800 IU, to a
placebo among 2,002 men and women with clogged
arteries showed a large benefit for E: those
taking supplements had a 77% reduced risk of
nonfatal heart attack over the next 1-3 years.

There is no consensus about the optimal amount
of E people should take. Doses up to 800 IU are
considered safe for most individuals. However,
people taking warfarin and other anticoagulant
medications should check with their doctor
before downing E supplements because large doses
can amplify the effects of these agents and
increase the risk of internal bleeding.

Scientists suspected that vitamin C and
beta-carotene would also prevent heart disease,
but most of the research to date has not borne
this out. Evidence from observational studies,
however, suggests that getting carotenoids
through food may lower coronary disease risk.
Beta-carotene is just one of several hundred
carotenoids contained in dark green, yellow, and
orange fruits and vegetables.

Cancer Protection

The strongest evidence that antioxidants may
prevent cancer comes from epidemiologic studies
that compared people who ate a lot of fruits and
vegetables, which are rich in the compounds, to
those who didn't. Indeed, hundreds of
investigations from around the world have found
an association between a plant-rich diet and a
lower risk of colon, stomach, lung, breast, and
prostate malignancies. The American Cancer
Society estimates that about one-third of US
cancer deaths are linked to diets low in fruits
and vegetables and high in fat. The best way to
get a variety of antioxidants, as well as other
beneficial plant chemicals, is to eat an
assortment of fruits and vegetables.

A good rule of thumb is to consume at least
three colors each day because plants with
different pigments are thought to contain
different antioxidants. There is some evidence
that lycopene, for example, a carotenoid found
in tomatoes that makes them red, may lower the
risk of prostate cancer. The body best absorbs
Lycopene when tomatoes are cooked; tomato paste
and sauce are good sources of the substance.

Clinical trials examining the protective effect
of individual antioxidant supplements on cancer
rates have generally come up short, with the
following possible exceptions: Data from the
Finnish smokers trial pointed to an association
between vitamin E and prostate cancer risk.
Among 30,000 male smokers, those who took 50 IU
of E daily were 32% less likely to develop
prostate cancer, and 41% less likely to die from
it, than those who didn't take E supplements.

There is promising preliminary evidence from an
observational study and one small clinical trial
indicating that the mineral selenium may protect
against prostate cancer and possibly lung, colon,
and esophageal malignancies. However, experts
believe it's still too early to recommend that
people take selenium supplements.

Vision Problems

Scientists theorize that free radicals play a
role in causing cataracts by damaging the
proteins in the lens of the eye. There is some
evidence that the antioxidant vitamins C, E, and
beta-carotene may reduce the risk of developing
cataracts.

Meanwhile, the carotenoids appear to be the key
antioxidants in preventing macular degeneration,
the progressive deterioration of the macula, the
central portion of the retina. (For more on
macular degeneration, see Harvard Health Letter,
August 1998.) In a 1994 study published in the
Journal of the American Medical Association,
researchers compared the dietary habits of 356
people with macular degeneration to 520 controls
who did not have the eye disease.

People with the highest reported consumption of
carotenoids had a 43% lower risk of macular
degeneration than those with the lowest dietary
intake. The beneficial effect may have been due
to lutein and zeaxanthin, antioxidants found in
dark green, leafy vegetables that also exist
naturally in the retina.


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Article submitted by Tim Delaney. References
include Nzymes at http://www.nzymes.com and
Nzymes EU at http://www.nzymes.eu.com


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