Vitamins and exercise don’t mix?

A new report in the latest issue of the Proceedings of the National Academy of Sciences has caused a stir. As Scientific American puts it,

Exercise is good for you. Antioxidants are good for you. But put them together and it’s not as good as you’d think. Because a recent study shows that some vitamins block the beneficial effects of exercise.

We’ve long thought that “free radicals” are harmful molecules that damage our cells and play a key role in the aging process. Antioxidants help mop up free radicals in our bodies, which is a key reason people advocate taking lots of vitamin C and E — particularly after hard exercise, which triggers the production of free radicals. But the new study found that exercisers who took antioxidant supplements didn’t improve their insulin sensitivity (a key factor in obesity and diabetes risk), while a control group that received placebos did.

This is by no means the first study to cast doubt on the “conventional” picture of how antioxidants and free radicals interact in the body. Indeed, the lead researcher in the new study, Michael Ristow of the University of Jena in Germany, published a study back in 2007 that made similar inferences:

Free radicals are usually considered harmful, Ristow said, and scientists have generally thought that exposure to them would shorten life span. The new findings suggest that, at least in some cases, the opposite may be true… Ristow called the result “scary” because it means that, rather than being protective, antioxidant pills may actually leave the body more vulnerable by thwarting those natural defenses.

That study was in worms, but the new study was in real people. Of course, human metabolism is so complex that few substances are likely to be entirely good or entirely bad. The researchers are quick to point out that antioxidant-rich foods still come highly recommended — but they suggest that those popping large doses of antioxidant supplements may be getting more (or less) than they bargained for.