For a while, it looked as if quercetin might be the next super-supplement, one of the few legal substances able to improve athletic performance. Quercetin is a flavonoid found naturally in apple skins, berries, red wine, black tea and some leafy vegetables. Like other flavonoids, it is believed to be an antioxidant, a substance that can lessen or prevent certain kinds of cell damage, and an anti-inflammatory. But of even more importance to athletes, it has shown evidence of being a potent performance enhancer in mice.A number of studies were done on humans. None of them showed similar results. The largest was done by the University of Georgia, financed by Coca-Cola, which was testing a new sports drink with quercetin.
In a representative animal study, published earlier this year, lab mice ran on a wheel or treadmill to gauge their fitness. Then some mice received large doses of quercetin for a week; others received a placebo. None of the rodents exercised. At the end of the week, the mice ran again. The quercetin mice were able to run as much as 37 percent longer than they had the week before. The placebo group showed no improvement. Meanwhile, analysis of the muscles and brains of some of the quercetin group showed new mitochondria — which help to produce energy — packing the cells. The placebo group had no new mitochondria. All indications, then, were that quercetin was energizing the mice at a fundamental, cellular level. …
The dosage of quercetin mimicked the amount given to mice, adjusted to human size. … At the end of [the study], the subjects were [tested], with provocative results. “There were simply no differences” between the quercetin and the placebo group, says Kirk J. Cureton, a professor of kinesiology at the University of Georgia and lead author of the study. The quercetin group didn’t ride farther before exhaustion. Their bodies showed no evidence of new mitochondrial production.
“We were surprised,” Cureton says. “Based on the mouse studies, we had expected” that the supplement would have a positive impact. Obviously, he continues, one study is not definitive. Different doses of quercetin or use for a longer time might lead to different results. “But my conclusion is that it just is not ergogenic in humans,” Cureton says. It doesn’t improve performance. “The moral is that you can’t generalize from mouse studies to humans.” And you can’t, as anyone who has followed sports nutrition should perhaps have learned by now, expect improved performance to be delivered, without effort, in pill or liquid form.