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April 10, 2000 (Atlanta) -- Physical exercise and fish oil are well documented as powerful tools in preventive medicine. However, there is a flip side to both -- namely, oxidative stress -- especially for athletes training to exhaustion. A new study in the March edition of Medicine and Science in Sports and Exercise shows that vitamin E can combat these harmful effects.

Though the human body needs oxygen, as much as 5% of the oxygen absorbed during normal activities is transformed into a form -- called oxygen "free radicals" -- that is harmful to healthy cells. This biological process, known as oxidative stress, can damage cells and decrease performance in athletes. "During exercise, oxidative stress can increase by four- to fivefold," researcher Chandan K. Sen, PhD, tells WebMD. The American Heart Association has a long-standing position that antioxidants such as vitamins C and E can minimize the development of oxidative stress by countering the effects of oxygen free radicals on arteries.

As for fish oil in the diet, Sen points out that fish can increase the amount of oxidation taking place; that, in turn, may cause oxidative damage to various tissues. Sen says that although exercise and fish oil have a lot of powerful beneficial effects, there is this undesirable effect, also. "If we can control that, perhaps we could enhance the overall beneficial effect of exercise," he says. "Understanding of the strategies that may minimize the ravages of oxidative stress is therefore central to our well-being."

In the study -- which actually was a sequel to a similar one conducted by the researchers and reported earlier -- rats were fed fish oil and then subjected to exhaustive exercise. Researchers discovered that a fish oil diet caused oxidative damage to lipids, while exhaustive exercise caused oxidative damage to both lipids and proteins. Vitamin E supplementation protected against oxidative damage caused by both fish oil and exercise.

"Our current study noted that fish oil diet up-regulates the activity of major antioxidant enzymes in various tissues," says Sen. "This effect could be viewed as a defense response designed to protect the organs." Sen is a principal investigator and staff scientist at the Lawrence Berkeley National Laboratory at the University of California, Berkeley. He is also a fellow of the American College of Sports Medicine.

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