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.
The researchers discovered that both exercise and fish oil deplete an important antioxidant called glutathione. Although the body doesn't manufacture its own vitamin C or E, it does make glutathione. "Glutathione has been shown to actually extend the life of vitamin E and C," says Sen. "When glutathione is depleted, it decreases the activity of other nutritional antioxidants."
When vitamin E is discussed, the most common form mentioned is alpha-tocopherol. In both studies, alpha-tocopherol was the vitamin E tested. According to Sen, he and his colleagues recently studied another form of vitamin E, alpha-tocotrienol, which is present in rice bran, palm oil, and various other natural food sources. They found that the tocotrienols may protect brain and nerve tissues, and they were more potent than the commonly used alpha-tocopherol. Sen and his team believe that oxidative stress may be prevented by dietary means.
No doubt, exercise and fish oil can enhance physical well-being, but they can also produce harmful biological effects. "The best way to combat these negatives is antioxidant supplementation," says Sen. "And vitamin E is a good candidate."
Although it believes in the importance of antioxidants, the American Heart Association says that scientific evidence does not yet support recommending vitamin E or other antioxidant supplements. Rather, the organization recommends that people increase their consumption of antioxidant-rich foods such as vegetables, fruits, and whole grains.
A statement released in February 1999 by Diane Tribble, PhD, who is a member of the American Heart Association's volunteer nutrition committee and also at Lawrence Berkeley National Laboratories, states that although some studies have shown that foods rich in antioxidants are associated with a reduced risk of heart disease, "that doesn't necessarily mean that high levels of antioxidants achieved by consuming vitamin pills will provide similar benefits -- or are even safe."
As for fish oil, the AHA position states that the benefits and risks of eating fish oil still need to be defined by further research. "Until there is compelling evidence that fish oil supplements (capsules) benefit overall cardiovascular health, the AHA does not recommend their general use," it states.
- Although fish oil and exercise have both been shown to have positive health benefits, they are also known to increase oxidative stress on the body.
- In an animal study, vitamin E, an antioxidant, was able to combat oxidative stress induced by fish oil and exercise.
- The American Heart Association does not recommend vitamin E or fish oil supplements because of a lack of conclusive scientific evidence, but it does encourage people to eat antioxidant-rich foods.