Thursday, February 17, 2011

Supplement Sabotage: Can antioxidants hamper muscle endurance?

One theory of aging, first proposed in 1957, suggests that substances called free radicals, or reactive oxygen species, gradually damage cells, resulting in an acceleration of the aging process. Free radicals are strongly implicated in the onset of many diseases linked to early mortality, such as cardiovascular disease, cancer and degenerative brain diseases.

You may remember from Chemistry 101 that electrons come in pairs. Free radicals are unpaired electrons and are constantly seeking to combine with electron pairs. When that biochemical menage à trois does occur, it wreaks havoc on cellular structures—for example, cell membranes—and lead to cell destruction.

Some scientists claim that cells are bombarded by some 10,000 free radicals per minute. Fortunately, we’re not defenseless against cellular terrorism. The body has a built-in system of antioxidant enzymes—including superoxide dismutase, catalase and glutathione peroxidase—that can neutralize the attacks. The sheer magnitude and relentlessness of free radicals are nevertheless capable of overwhelming the body’s defenses. Additionally, many of the body’s defenses diminish with age, which may play a role in diseases that are more prevalent among older people, such as cancer and heart disease.

Dietary antioxidants, mainly from fruits and vegetables, back up the body’s antioxidant defenses. You’re probably familiar with many of them: vitamins C, E, B-complex and A, plus various minerals, as well as plant compounds called bioflavonoids and polyphenols. The latter are especially plentiful in green tea, red wine and dark chocolate.

Oddly enough, free radicals offer a few significant health benefits. For one thing, they’re produced by immune cells as a means of destroying invading toxic organisms, such as bacteria. They’re required for the production of thyroid hormones. One dietary antioxidant mineral, selenium, is essential for activating the enzymes that help generate thyroid hormones. Because of its antioxidant properties, however, too much selenium doubles back and inhibits thyroid hormone.

A lesser-known benefit of exercise is that it offers antioxidant protection, and some researchers say that the major health benefit of exercise is that it upgrades antioxidants, a process known as hormesis. The term refers to how exposure to small doses of a toxic substance results in compensatory beneficial effects. [Editor’s note: For more information  on hormesis, see page 300 of the July '08 issue of IRON MAN.]

The increased oxygen intake that exercise generates also creates oxidative stress, which  in turn generates free radicals. When that happens, several negative conditions can result. One is excessive muscle damage, which can delay training recovery. That’s the reason athletes are often advised to get a generous amount of dietary antioxidants—and most don’t rely on food but supplement with vitamins C and E and minerals.

The research is contradictory on whether the dietary antioxidant boost is necessary. Studies show that merely continuing to exercise automatically bolsters the body’s antioxidant system via hormesis. What’s more, while some studies have found that elite athletes generate higher-than-normal free radicals when training, others have found the opposite.

A recent controversial study, which used both animal and human subjects, suggests that adding vitamin C to your supplement regimen may actually hamper endurance gains from training. Fourteen sedentary men underwent eight weeks of endurance training, during which five of the subjects took one gram (1,000 milligrams) of vitamin C daily. Meanwhile, 24 rats went through three- and six-week training routines; half the rats were given a dose of vitamin C species-equivalent to the human dose. The men who didn’t take vitamin C showed a 22 percent increase in their body’s ability to take up and use oxygen during training, while those who supplemented with C showed only a 10.8 percent increase. Similar results occurred in the rats.

Exercise tests revealed that when forced to run to exhaustion after six weeks of training, the rats not given vitamin C ran almost twice as far as they had before training, amounting to a 186.7 percent increase in endurance capacity. Those that got vitamin C, however, increased their distance by only 25 percent, or a 26.5 percent increase in endurance. The rats not given vitamin C showed higher counts of mitochondria, the portions of cells where energy is produced as ATP and where fat is oxidized. The amount of mitochondria determines endurance, and aerobics increases endurance by generating the production of additional mitochondria.

What gives with those results? It turns out that the production of free radicals from exercise stimulates the production of new mitochondria. Taking vitamin C short-circuits the process. Taking vitamin C prior to exercise also prevented the exercise-induced stimulation of built-in antioxidant enzymes, such as superoxide dismutase and glutathione peroxidase.

Several previous studies have reported unfavorable effects on endurance development due to dietary antioxidants, such as vitamin E and coenzyme Q10. One study published seven years ago found that taking a combination of vitamin E and alpha lipoic acid reduced muscle contractile activity, which would translate into reduced exercise strength.

Another recent study, however, had very different findings. Thirty-six students supplemented their diets with 400 milligrams a day of vitamin E, 1,000 milligrams of vitamin C or a combination of both nutrients for three weeks. Another group got a placebo. The subjects underwent various tests that measure aerobic and anaerobic exercise performance. Those who got the antioxidant nutrients performed significantly better on the aerobic tests than the placebo group. The anaerobic tests showed no differences in ether group. The study concluded, “These test results suggest that daily supplementation with vitamin E (400 units), vitamin C (1,000 milligrams) or vitamin E plus vitamin C for a period of three weeks may significantly improve aerobic power.”


Gomez-Cabrera, M.C., et al. (2008). Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance.Am J Clin Nutr. 87:142-149.

Coombes, J.S., et al. (2001). Effects of vitamin E and alpha lipoic acid on skeletal muscle contractile properties. J Appl Physiol. 90:1424-30.

Jourkesh, M., et al. (2007). The effects of vitamins E and C supplementation on bioenergetics index. Res Sports Med. 15:249-56.