Free radicals, exercise and antioxidant supplementation

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Abstract
Although conflicting data exist, the preponderance of available information suggests that physical exercise promotes an increase in free-radical generation. However, few studies have actually measured exercise-induced free radicals directly, primarily because of a lack of sophisticated methodologies to measure this phenomenon. Instead, researchers have relied heavily on the measurement of lipid peroxidation as the principal indicator of exercise-induced free radicals. It should be noted that free radicals can also alter and inactivate enzyme complexes, damage DNA and RNA, and promote mutations and cancer, among other activities. However, there have been few reported studies dealing with exercise and oxidant stress which have measured these outcomes. It should also be noted that free-radical species are continuously produced in the human body, and that some have beneficial effects (Arouma, 1994), notably as a part of the body's natural immune system. It is not presently known if long-term ingestion of antioxidant compounds will affect these positive aspects of free-radical generation. The preponderance of available evidence suggests that antioxidant supplementation, particularly with the vitamins C and E, has favourable effects on markers of lipid peroxidation following exercise. Although the physiological implications of these effects remain to be elucidated, the prudent use of an antioxidant supplement can provide insurance against a suboptimal diet and/or the elevated demands of physical activity. Future research may uncover additional nutritional antioxidants that can benefit the physically-active individual. Numerous additional questions regarding the antioxidant needs for physical activity remain to be answered. Little is known about the needs of physically-active women, particularly those who habitually consume an energy-restricted diet, or the effects of monthly menstrual blood loss (coupled with exercise) on antioxidant requirements. The needs of the 'weekend warrior' (an individual who participates in strenuous activity sporadically) v. those of the habitual exerciser have not been addressed adequately. The needs of the ageing athlete are largely unknown; a study by Meydani et al. (1993) suggested that elderly, physically-active people can benefit from antioxidant supplementation more than their younger counterparts, but follow-up studies have not been reported to-date. Dietary issues also need to be addressed. How much supplementation is too much, and can chronically-elevated antioxidant intakes have an adverse impact on the positive effects of free radicals in living systems? Does a high-carbohydrate diet raise antioxidant needs, particularly of the fat-soluble vitamin E? Does a high polyunsaturated fat intake, or increased Fe intake affect needs? Obviously, there are a number of issues regarding the antioxidant needs of the physically-active individual that need to be elucidated. Future research utilizing newer, more sophisticated methodologies should provide answers to many of these questions.
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