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Antioxidants: More Harm Than Help?

Various antioxidant nutrients, such as vitamins E and C, are a typical component of bodybuilding diets. Most bodybuilders use supplements containing antioxidants in addition to what they get naturally in food. Antioxidants have been touted for their ability to aid exercise recovery, including relieving excessive muscle soreness. They block the effects of free radicals, which are unpaired electrons produced in the normal course of metabolism, including oxidation. Simply put, if you breathe, you produce free radicals.

The problem is, free radicals tend to attack fatty cell membranes, and that can cause a number of serious health problems ranging from cardiovascular disease to cancer to premature aging.

Antioxidants sacrifice an electron in order to neutralize the potential dangers of rampant free-radical activity. That turns them into pro-oxidants capable of producing free radicals, but it occurs only in isolation. The reason natural foods often contain several antioxidants is that the antioxidants revitalize each other, converting those that have been oxidized through exposure to free radicals back into true antioxidants.

From the point of view of exercise, the increased oxygen intake that occurs during exercise also produces more free radicals. Some studies have linked the greater presence of free radicals during exercise to fatigue. Some have suggested that athletes or those engaged in intense exercise should consider taking antioxidants. On the other hand, exercise itself is a potent impetus for the body to produce its own antioxidants. The body’s built-in antioxidant defense system consists mostly of enzyme systems, such as superoxide dismutase, catalase and glutathione, that can rapidly block free-radical damage.

Scientists are divided on whether antioxidant supplements offer any protection above and beyond that produced by the exercise-induced stimulation of the body’s native antioxidant systems. Some researchers suggest that the free-radical production during exercise is more than the body’s ability to cope with it and that taking antioxidants bolsters the body’s natural defense system. Those studies are paradoxical, however. Some have found added protection from using antioxidants, while others have found little or none.

While free radicals have been portrayed as villains, they do offer useful benefits. One example is related to immune function. Some immune cells kill bacteria by bombarding the noxious invaders with free radicals. Free radicals are also involved in the production of thyroid hormone, and taking excessive amounts of some antioxidants, such as selenium, can actually lower thyroid hormone output. Perhaps the most interesting recent research concerning free radicals is that they act as signaling devices in muscle recovery and growth. Indeed, nitric oxide, one such signaling substance, is a free radical. Many bodybuilders use supplements touted to boost NO in the body, unaware that it’s a free radical. In excess it combines with oxygen to form the potent and dangerous free radical peroxynitrate.

The fact that free radicals impart some benefits to muscle—one recent study found that they trigger local release of IGF-1, an anabolic hormone, in muscle during exercise—has led some researchers to question the wisdom of using antioxidant supplements if you’re involved in athletics or intense exercise. Some studies, mostly involving animals, have shown that antioxidant supplementation may even lessen the beneficial effects of exercise. One study found that the development of mitochondria—cell organelles where energy is produced and fat is oxidized—is blunted when subjects got antioxidants after exercise. The study suggested that free radicals directly stimulate mitochondria production, particularly after endurance exercise—an idea that, if true, has broad implications. Many medical problems are related to mitochondrial defects, including cardiovascular disease and diabetes. One theory suggests that aging itself results from a gradual loss of cellular mitochondria, muscles being particularly affected because they use so much energy.

The studies that showed negative effects of antioxidant supplements often iinvolved animals or human subjects who already had medical problems, such as insulin resistance. Would the same effect occur if young, healthy and fit subjects took antioxidants? That was the focus of a new study.1 Twenty-one young, healthy men, average age 29, were randomly assigned to either an antioxidant or a placebo group. Those in the antioxidant group got 500 milligrams of vitamin C and 400 units of vitamin E daily with breakfast. Both groups also underwent an intense endurance training program five times a week for 12 weeks. The subjects were tested at the start of the study for maximum oxygen intake, maximum power output and body composition. They were again tested at the end of the study.

The authors cited previous studies showing that antioxidant supplements interfere with the benefits of endurance exercise and hypothesized that their experiment would confirm prior findings—but that’s not what happened. Although the supplements markedly raised blood counts of vitamins E and C, it turned out that glucose uptake, power and maximal oxygen intake were similar for both groups, indicating that the antioxidant had no negative effect whatever on the benefits of the exercise—contrary to previous findings. In explaining the results, the authors suggested that the subjects’ high degree of exercise intensity probably produced free radicals in numbers that exceeded what was quenched by the antioxidants, and that was enough to produce the benefits associated with endurance exercise.

Even so, the authors hedged on suggesting that antioxidants would prove beneficial to those who exercise, noting that the nutrients “didn’t provide any additional beneficial effect to the endurance training.” The fact that the supplements didn’t adversely affect any gains that could accrue from endurance exercise, however, offers some solace to those of us who use them.


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1 Yfanti, C.,et al. (2011). The effect of antioxidant supplementation on insulin-sensitivity in response to endurance training. Am J Physiol Endo Metabol. 300(5): E761-70.


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