GSSI Hot Topic Article, February 2002
NUTRITITIONAL ANTIOXIDANTS: ARE THEY ERGOGENIC?
Scott K. Powers, Ph.D., Ed.D.
Interest in the effects of dietary antioxidants on exercise performance has grown rapidly during the past several years. The purpose of this article is to provide a brief overview of current knowledge on dietary antioxidants and exercise performance.
Free Radicals and antioxidants – What are they?
Free radicals (radicals) are damaging molecules that are produced during normal cellular metabolism. Radicals can damage cells by reacting with cellular components; this type of damage is called oxidation and can result in serious injury to cells. Given that radicals are produced during normal metabolism, it is not surprising that cells contain antioxidants (molecules that eliminate radicals) to reduce the risk of radical-mediated injury.
Two major classes of antioxidants work together in cells to reduce the harmful effects of radicals: 1) enzymatic and 2) non-enzymatic antioxidants.
Enzymatic Antioxidants - Key antioxidant enzymes include superoxide dismutase, glutathione peroxidase, and catalase. These enzymes are manufactured in the cell and cannot be obtained through dietary supplementation.
Non-Enzymatic Antioxidants - Important non-enzymatic antioxidants include vitamins E and C, and b-carotene. These antioxidants are included in many foods and can also be obtained through dietary supplements. Vitamins E and b-carotene protect cell membranes from radical damage. Vitamin C works in conjunction vitamin E to protect both fatty substances and proteins in the cell from radical damage.
Can dietary antioxidants improve exercise performance?
Although regular exercise produces many positive health benefits, it also causes an increased production of free radicals. Indeed, intense or prolonged exercise can cause radical-mediated injury to skeletal muscles, particularly in untrained individuals. Further, radicals probably contribute to muscular fatigue during endurance events. Therefore, it is not surprising that there is strong interest in the effects of antioxidant supplements on exercise performance.
Numerous animal studies indicate that antioxidant supplements can delay muscular fatigue. Nonetheless, most animal studies have used antioxidant treatments that cannot be used in humans, so these results should not be directly extrapolated to humans.
Only a few studies have examined the effects of antioxidant supplementation on muscular endurance in humans. Further, many of the studies were flawed, and most studies have investigated the effects of a single antioxidant rather than the combined effects of several antioxidants. Although several human studies indicate that supplementation with vitamin E, and/or vitamin C reduce exercise-induced radical injury, there is limited evidence that antioxidant supplementation can improve human athletic performance. However, because of the paucity of research on this topic, additional studies are required before a firm conclusion can be reached about the effects of antioxidant treatment on human exercise performance.
Should athletes use antioxidant supplements?
Because prolonged and/or intense exercise produces radicals, should athletes consume antioxidant supplements on a regular basis? There is little scientific support for antioxidant supplementation in athletes who consume a well-balanced diet that is rich in fruits and vegetables. Further, over-consumption of antioxidants may have potentially harmful side effects, because high levels of some antioxidants can be toxic. For example, extreme doses of vitamin E have been reported to impair muscular performance in animals. Therefore, athletes considering the use of antioxidant supplements should seek the advice of a well-trained nutritionist prior to adding these supplements to their diet.
Click here for a biography of Dr. Scott Powers.