Should Runners Take Antioxidants During Exercise?

Australian researchers suggest it may be best to let free radicals do their thing.

Sometimes there’s a subtle difference between an aid and a crutch. An aid is a tool that elevates performance. A crutch is a tool that makes it easier to perform and thereby weakens one’s ability to perform without the benefit of that tool. Often it is difficult to distinguish between a tool and a crutch. There are many examples of this fine line in exercise. For example, a pull buoy can be used to teach proper body position in freestyle swimming. But an athlete who overuses a pull buoy may become dependent on it and unable to achieve a correct body position without it.

In recent years, exercise scientists have been trying to figure out whether antioxidant supplementation during exercise is an aid or a crutch. This question is not yet settled, but a pair of Australian researchers have published a scientific review that leans toward declaring antioxidant supplementation during exercise a crutch.

Here’s why. As everyone knows, the working muscles process a lot of oxygen during exercise. Some of the oxygen molecules that the muscles use to release energy become free radicals, or what scientists prefer to call reactive oxygen species. Free radicals are known to cause muscle damage and impair muscle function, hastening fatigue.

As everyone also knows, antioxidants are compounds that counteract free radicals. Some antioxidants are endogenous, meaning the body makes them. Others are exogenous, entering the body as nutrients. Vitamins C and E, carotenoids, and polyphenols are examples of the latter.

Given this knowledge, it was inevitable that some people would begin to wonder whether taking in supplemental antioxidant nutrients during exercise could reduce muscle damage and enhance performance. It was inevitable also that some companies would begin to make products containing antioxidants and intended for use during exercise before this question was answered.

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Within the past several years, a large number of studies have attempted to answer the question. Two scientists at the University of Queensland, Australia, Tina-Tinkara Peternelj and Jeff Coombes, looked over more than 150 of these studies in an attempt to discover what sort of answer they arrived at in sum. By and large they were unimpressed, observing that most of the studies were too small and too poorly designed to be of much value.

Nevertheless, we know a lot more than we did before these 150 studies were conducted, Peternelj and Coombes say. One thing that seems certain is that supplementation with antioxidants during exercise reduces oxidative stress in the muscles. “However,” the authors of the review caution, “any physiological implications of this have yet to be consistently demonstrated, with most studies reporting no effects on exercise-induced muscle damage and performance. Moreover, a growing body of evidence indicates detrimental effects of antioxidant supplementation on the health and performance benefits of exercise training.”

In other words, by reducing oxidative stress in the muscles, antioxidants taken during exercise may function as more of a crutch than as an aid. How so? Well, in addition to causing muscle damage and impairing muscle function, free radicals also stimulate physiological adaptations that increase fitness. Consequently, when free radicals are prevented from performing their full actions by antioxidants consumed during a workout, that workout may yield less benefit.

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In this sense, antioxidants could be said to function like an overzealous spotter in a weightlifting workout. Weightlifting makes the muscles stronger by subjecting them to stress and breakdown that trigger an adaptive response. If you lift weights with an excessively helpful spotter who takes half the load away from you in every bench press and every squat, your muscles will be subjected to less stress and breakdown and will therefore get less benefit from the session.

According to the new review out of Australia, high doses of certain antioxidants taken during exercise seem to be analogous to this overzealous spotter. So what does this mean for you?

“More research is needed to produce evidence-based guidelines regarding the use of antioxidant supplementation during exercise training,” Peternelj and Coombes conclude. “We recommend that an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain the optimal antioxidant status in exercising individuals.”

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About The Author:

Matt Fitzgerald is the author of Iron War: Dave Scott, Mark Allen & The Greatest Race Ever Run (VeloPress 2011) and a Coach and Training Intelligence Specialist for PEAR Sports. Find out more at mattfizgerald.org.