Physical Exercise and Antioxidants

During exercise, oxygen consumption can temporarily increase by a factor of more than 10. This leads to a temporary large increase in the production of oxygen free radicals, resulting in increased cell damage contributing to muscular fatigue during and after exercise. The body uses antioxidants to reduce the amount of such damage. The inflammatory response that occurs after strenuous exercise is also associated with increased occurrence of free radicals, especially during the 24 hours after an exercise session. In this phase too, antioxidants in the body reduce the damage. The immune system response to damage done by exercise peaks 2 to 7 days after exercise, the period during which adaptation resulting in greater fitness is greatest. During this process, free radicals are used by neutrophils in the immune system to identify damaged tissue. As a result, excessive antioxidant levels have the potential to inhibit recovery and adaptation mechanisms.

There is a popular view that those who undertake vigorous exercise can benefit from increased consumption of antioxidants, but an examination of the literature finds support that this is the case only for certain antioxidants at certain levels, and some evidence that very large intake of some antioxidants may be detrimental to recovery from exercise. There is strong evidence that one of the adaptations that result from exercise is a strengthening of the body’s antioxidant defenses, particularly the glutathione system, to deal with the increased oxidative stress. It is possible that this effect may be to some extent protective against diseases which are associated with oxidative stress, which would provide a partial explanation for the lower incidence of major diseases and better health of those who undertake regular exercise.

The antioxidant system that protects lipid membranes from free radicals includes vitamin E, beta-carotene, vitamin A, and coenzyme Q10. The system that scavenges free radicals in the water based cytoplasm includes vitamin C, glutathione peroxidase, superoxide dismutase, and catalase. The effect of each of the exogenous antioxidants needs to be examined separately, although they work in a co-operative manner.

The body of research suggests no benefits from supplementing with vitamin A above normally recommended levels. Recent well-designed studies suggest there are no ergogenic benefits from vitamin E (except for those who do exercise at high altitude) despite its key role in preventing lipid membrane peroxidation. For example, 6 weeks of vitamin E supplementation had no effect on muscle damage indicators in ultramarathon runners. Although selenium is essential to the glutathione antioxidant system which, as mentioned above, is upregulated by exercise, there is no evidence that supplementation with selenium above the RDA is of any ergogenic benefit. However, for vitamin C there is considerable evidence that vitamin C requirements are greater in those who do vigorous exercise, with plasma levels falling with intake of 100mg (well over the accepted RDA) and around 300mg per day being required to maintain blood plasma levels. There is some evidence that supplementation with vitamin C increased the amount of intense exercise that can be done, and lowered the heart rate while doing it (which is indicative of greater efficiency), and that vitamin C supplementation before strenuous exercise reduces the amount of muscle damage. However, some other studies found no such effects, and some research suggests that supplementation with amounts as high as 1000 mg inhibits recovery, although the very short pre-exercise supplementation period in this study may have influenced the results. There is strong evidence that vitamin C supplementation reduces upper respiratory tract infections in ultra-endurance athletes.

In summary, a diet with at least 300 mg of vitamin C is of benefit to those who undertake high intensity or high volume exercise, but it is not clear that normal requirements for vitamin A, vitamin E or selenium are increased.

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