Supplement watch: quercetin for endurance

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Quercetin is an antioxidant found in berries, fruit skins, black tea, red wine, and a few other places. It has generated some excitement because it has been shown to increase the production of mitochondria and enhance running endurance by 37 percent in mice. Human studies (it almost goes without saying) have produced less spectacular results — and now an excellent double-blind, placebo-controlled trial by researchers at the University of Georgia, published in the Journal of Applied Physiology, has failed to find any effect on a whole series of athletic performance markers in humans.

“We did not see any performance enhancing effect of quercetin,” [researcher Kirk] 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.”

The press release (from which the above quote is taken) is unusually well-written and provides lots of details on the study and its significance and context. The researchers cast their net pretty widely, looking for possible effects. They measured:

• The rate at which muscles synthesize energy after strenuous exercise;
• Peak oxygen consumption;
• The rate of perceived exertion during cycling;
• Metabolic changes, such as the percentage of energy derived from fats and carbohydrates (more conditioned individuals tend to use more fat for energy);
• Performance on a cycling test; and
• Strength loss following prolonged cycling.

In none of these cases did they find any performance enhancement. The last word to the researcher:

“The take home message here is that promising results in mice don’t necessarily translate to humans,” Cureton said.