Emory Scientists Study How Anti-Oxidants
May Help -- or Hurt -- Heart Health
Fitness 2001 Participants Can Help Measure Relationship Between Exercise
and Antioxidants
According to popular consumer books on nutrition, antioxidants
like vitamin C, E and beta carotene are panaceas of health that can
help prevent heart disease. Now, an internationally recognized expert
on antioxidants and their role in health, Emory scientist Sampath Parthasarathy,
Ph.D., says taking antioxidants - at least when you first start to exercise
- could potentially endanger your heart health.
In the October issue of the medical journal Arteriosclerosis, Thrombosis
and Vascular Biology (2001 21: 1681-1688), Dr. Parthasarathy, director
of the Division of Research in Emory University's Department of Gynecology
and Obstetrics, and his team of researchers report a study in mice that
concludes exercise-induced oxidative stress could be responsible for
the prevention of atherosclerosis by stimulating the body to manufacture
its own antioxidant enzymes. However, taking antioxidant supplements,
specifically vitamin E, could negate this natural, heart disease fighting
process, the scientists state.
Does this theory hold up in people? To find out, Dr. Parthasarathy
is conducting a study with Emory Heart Center cardiologist William Weintraub,
M.D., involving 500 volunteers. The researchers hope to answer a number
of intriguing questions about the relationship between exercise and
antioxidants. For example, how long, how intense and how often should
one exercise to convert oxidative stress into an antioxidant defense?
"We will also find out, potentially, if vitamin E is harmful," says
Dr. Weintraub, director of Emory's Center for Outcomes Research. "This
goes against prevailing thought, but we want to see if it might block
the body's ability to develop its own antioxidant defenses."
The Fitness 2001 study will look at the fitness levels of 250 women
and 250 men between the ages of 18 and 70, who do not exercise, have
no evidence of heart disease and who do not take vitamin supplements.
The scientists will monitor the research subjects' oxygen consumption
while the participants work out on a treadmill to determine their fitness.
The study participants will also answer simple questions about their
eating habits and how much time they exercise. Then they will be instructed
to exercise at their own pace, three times a week for half an hour for
two months. At the beginning of the study, and at two, four and six
week intervals, the scientists will measure the study participants'
cholesterol levels as well as check their blood for specific markers
of oxidative stress. Exercise tests will also be repeated to make sure
the subjects are exercising and improving their fitness levels.
"We are hoping that over the two months, the subjects will begin in
the oxidation phase and then we will see them entering the antioxidant
phase," Dr. Parthasarathy explains. "Our hypothesis predicts that the
cholesterol lowering benefit that exercisers get involves oxidative
stress. If people don't get the oxidative stress — if they take antioxidants
during this period of starting exercise — they will not lower their
cholesterol."
In the late l980s, Dr. Parthasarathy was part of a research team that
concluded oxidation plays a major role in the development of cardiovascular
disease. Oxidation constantly takes place inside cells generating molecules
that form "free radicals" that have the potential to damage body cells
and tissues. Dr. Parthasarathy specifically asserted that oxidation
of low density lipoprotein (LDL) by free radicals causes LDL to enter
blood vessel walls and deposit cholesterol instead of being removed
from the body through the liver. This theory gained acceptance in the
cardiology community and helped promote the popularity of antioxidants
—nutrients and other substances that stabilize free radical molecules,
helping to prevent, inhibit or delay oxidative damage.
Dr. Parthasarathy is quick to point out that the relation between antioxidants
and free radicals and the development of coronary artery disease is
far more complex than the idea "oxidation is bad and antioxidants are
good." Here's why: exercise produces oxidative stress in the body, spurring
the production of free radicals that, in turn, oxidize LDL and lead
to vessel clogging atherosclerosis. So, theoretically, exercise should
trigger coronary heart disease. However, evidence strongly suggests
regular exercise does just the opposite - it lowers the risk for heart
disease.
The paradox can be explained by the fact exercise increases blood levels
of the body's own antioxidant enzyme. "I compare exercise to a vaccine,"
says Dr. Parthasarathy. "Instead of injecting bacteria, exercise injects
oxidation as a 'vaccine' which in turn leads to the body developing
antioxidants."
Learning specifically how exercise can protect heart health — and lead
to regression of heart disease — will play a key role in the future
of cardiology, Dr. Parthasarathy predicts. "There is overwhelming evidence
that even if someone has coronary artery disease, exercise can help.
It stops progression of heart disease and without progression you get
regression," Dr. Parthasarathy says.
He adds that the exact role of antioxidants in health remains unclear
and more research is needed on both natural and synthetic varieties.
"And we need to recognize that not everyone will benefit by taking antioxidant
supplements. In fact, some may cancel out the benefits of certain drugs,
such as cholesterol-lowering stating medications," Dr. Parthasarathy
says.
For information on enrolling as a participant in the Fitness 2001 study,
contact Dr. Parthasarathy's office at 404-727-8604.
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