Many people take vitamins as part of their daily fitness regimens, having heard that antioxidants aid physical recovery and amplify the impact of workouts. But in another example of science undercutting deeply held assumptions, several new experiments find that antioxidant supplements may actually reduce the benefits of training.
Antioxidants became popular dietary supplements largely because they were said to sop up free radicals, the highly reactive oxygen molecules that are generated during daily activities. Physical exertion, through its breakdown of oxygen, results in the creation of large numbers of these molecules, which, in excess, can lead to cell death and tissue damage. So it seems logical that reducing the number of free radicals produced by exercise would be desirable.
Enter antioxidants, which absorb and deactivate free radicals. While the body creates its own antioxidants, until recently many researchers believed that we produce too few natural antioxidants to counteract the depredations from free radicals created during exercise. So many people who exercise began downing large doses of antioxidants such as vitamins C and E, even though few experiments in people had actually examined the precise physiological impacts of antioxidant supplements in people who work out.
For a study published last week in The Journal of Physiology, researchers with the Norwegian School of Sport Sciences in Oslo and other institutions gathered 54 healthy adult men and women, most of them recreational runners or cyclists, and conducted a series of tests, including muscle biopsies, blood draws and treadmill runs, to establish their baseline endurance capacity and the cellular health of their muscles.
Then they divided the volunteers into two groups. Those in one group took four pills a day, delivering a total dose of 1,000 milligrams of vitamin C and 235 milligrams of vitamin E. Members of the second group got identical placebo pills.
Finally, they asked all of the participants to complete a vigorous 11-week training program, consisting of increasingly intense interval sessions once or twice per week, together with two weekly sessions of moderately paced hour-long runs. By the end, all of the volunteers were more fit than they had been at the start, with their maximum endurance capacity increasing by an average of about 8 percent.
But their bodies had responded quite differently to the training. The runners who had swallowed the placebo pills showed robust increases of biochemical markers that are known to goose the creation of mitochondria, the tiny structures within cells that generate energy, in cells in their bloodstream and muscles. More mitochondria, especially in muscle cells, means more energy and, by and large, better health and fitness. The creation of new mitochondria is, in fact, generally held to be one of the most important effects of exercise.
But the volunteers who had consumed the antioxidants had significantly lower levels of the markers related to mitochondrial creation. The researchers didn’t actually count the specific populations of mitochondria within their volunteers’ muscles cells, but presumably, over time, those taking the antioxidants would see a smaller uptick in mitochondrial density than among those not taking them.
That finding echoes the results of another study of antioxidant supplementation and exercise, also published last year in The Journal of Physiology, in which half of a group of older men downed 250 milligrams daily of the supplement resveratrol, an antioxidant famously found in red wine, and the other half took a placebo. After two months of exercising, the men taking the placebo showed significant and favorable changes in their blood pressure, cholesterol profiles and arteries, with fewer evident arterial plaques.
The men taking the resveratrol were not as fortunate. They had exercised as much as the other men, but their blood pressures, cholesterol levels and arteries had remained stubbornly almost unchanged.
Why and how antioxidant supplements would blunt the effects of exercise is not altogether clear, said Goran Paulsen, a researcher at the Norwegian School of Sport Sciences, who led the vitamin C and E study. But he and many other physiologists have begun to suspect that free radicals may play a different role during and after exercise than previously thought.
In this theory, free radicals are not villainous but serve as messengers, nudging genes and other bodily systems into starting the various biochemical reactions that end in stronger muscles and better metabolic health. Without free radicals, those reactions don’t begin.
And large doses of antioxidant supplements absorb most of the free radicals produced by exercise.
Of course, that theory is still unsubstantiated and requires long-term testing in people, Dr. Paulsen said. It is possible, he said, that smaller doses of antioxidants or different formulations might be useful for athletes. Meanwhile, natural antioxidants from food sources, such as blueberries and red wine, are unlikely to be problematic, he said. “It’s probably only concentrated extracts that are potentially dangerous,” he said. It is also worth pointing out that the volunteers who took the concentrated extracts of vitamins C and E increased their endurance to the same extent as those taking a placebo.
On the other hand, the supplements did not improve performance in comparison with a placebo, so why bother with them, Dr. Paulsen asked. “Personally, I would avoid high dosages” of antioxidants while training, he said. The science on the topic may not be complete, but the intimation of the recent studies is that by downing the supplements, “you risk losing some of the benefits of exercise.”