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October 31, 2001


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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