The antioxidant quercetin is increasingly being marketed as a supplement that boosts athletic performance, but a new UGA study finds that it is no better than a placebo.
Kirk Cureton, head of the department of kinesiology in the College of Education, and his colleagues tested quercetin in a double-blind, placebo-controlled study that assessed a variety of measures, including the ability of muscles to synthesize energy, cycling performance, perceived exertion and strength loss following exercise. The results appear in the August online edition of the Journal of Applied Physiology.
“We did not see any performance enhancing effect of quercetin,” Cureton said. “To a certain extent that was disappointing because our hypothesis, based on previous studies in mice, was that we would see positive effects. But our findings are important because they suggest that results from the animal studies shouldn’t be generalized to humans.”
Quercetin is a naturally occurring antioxidant found in the skins of fruits, leafy vegetables and berries as well as in black tea, red wine and various fruit juices. It is sold as a supplement in nutrition stores and is an ingredient in sports drinks such as FRS Energy, which is promoted by Lance Armstrong.
In mice, quercetin has been shown to stimulate the production of mitochondria, which are the energy producing components of muscle cells and other tissue. One study found that mice supplemented with quercetin increased running endurance by up to 37 percent.
In humans, however, the results have been mixed. An early and widely-cited study reported improvements in performance during a cycling time trial, but Cureton notes that data from the experimental group was not compared to the control group, making the statistical significance of the finding unclear. Published studies on competitive runners and cyclists have found no improvement in performance. A recent published study by the same researchers who reported mitochondrial and endurance increases in mice, however, found that volunteers who consumed a drink containing quercetin saw a 13 percent improvement in endurance. Cureton said the reason for the conflicting results is unknown, but added that several other studies currently in review for publication also have found no performance-enhancing effect.
Cureton and his colleagues hypothesized that the athletes used in the previous studies might not have benefitted from quercetin because they already had maximized their mitochondrial density through aerobic training.