A second look at antioxidants

One of the current fads in nutrition today is antioxidants -- vitamins like C and E that go after free radicals, molecules created by the breakdown of oxygen during metabolism.

"Each of us constantly creates free radicals simply by living and breathing, Tara Parker-Hope writes in The New York Times. "But these molecules are highly reactive and capricious, sometimes attacking other cells and damaging tissue. Wilding free radicals have been linked with a number of diseases and with aging."

Exercise, she writes, creates even more free radicals, and so athletes were encouraged to to lots of antioxidants. A few years ago, however, some researchers started fooling around with rats. One group got lots of antioxidants before exercise, the other got none. The antioxidant bunch showed no free radicals in their blood.

The leg muscles of the other exercised rats, though, teemed with free radicals. But at the same time, they buzzed with other, unexpected biochemical reactions. In their legs, genes were being expressed that activated growth factors that, in turn, increased levels of ‘‘important enzymes associated with cell defense’’ and ‘‘adaptation to exercise,’’ the researchers wrote. There was hardly any similar activity in the rats with low free-radical levels. Somehow, the researchers speculated, the free radicals had jump-started a process that over time would allow the rats’ muscles to adapt to exercise. Suppressing the production of free radicals had, they concluded, prevented the ‘‘activation of important signaling pathways’’ and altered the muscles’ ability to adapt to exercise. As a result, they wrote, ‘‘the practice of taking antioxidants’’ to ward off the presumed free-radical damage caused by exercise ‘‘may have to be re-evaluated.’’

Then another study last year, this time with humans.

A group of young men were enrolled in a month-long exercise program. Some swallowed moderately high doses of the antioxidant vitamins C and E. Others did not. At the end of the month, the men not taking the vitamins showed higher-than-average activity in their bodies’ innate antioxidant defense system. The men downing the vitamins did not, which makes sense; the antioxidant vitamins were mopping up the free radicals for them. But at the same time, the men not taking vitamins significantly increased their insulin sensitivity, a key measure of the health benefits of exercise, while those taking the antioxidants did not. Apparently, when the body’s natural antioxidant defense system went into high gear, so did its ability to handle insulin. Removing the necessity for the body to deal, on its own, with the free radicals also prevented other adaptations that make exercise healthy.

What does all of this mean?

‘‘The evidence suggests that antioxidants are not needed’’ by most athletes, even those training strenuously, said Li Li Ji, a professor of exercise physiology and nutritional science at the University of Wisconsin and one of the authors of the rat study. ‘‘The body adapts,’’ he said, a process that can, it seems, be altered by antioxidant supplements.


Another lesson: ‘‘Eat well,’’ he said. Although this is not yet proved, it seems likely, he continued, that antioxidants from foods, like blueberries, green tea and carrots, may work in tandem with the body’s natural antioxidant defenses better than those from supplements.

But the overriding lesson of the newest science about exercise and antioxidants may be as simple as: let the body be. ‘‘It is quite a smart machine,’’ Dr. Ji said. ‘‘It knows how to respond’’ to stresses like a hard run, without the need for antioxidant pills.

It's not clear how this affects people not consider "athletes," and that will be something to discover. But, in the Duh Department, it seems that if exercise is good for us, and we know it is, the body is wise in its own ways.