On Fitness

Athletes are always looking for (legal, they hope) ways to boost performance. They take caffeine, which has been shown to enhance endurance, and catch up on sleep, which also seems to improve fitness. And they often take handfuls of supplements in search of an extra edge. A small study published this week sheds light on one popular supplement—quercetin—which is being examined for its potential not only to improve athletic performance but also to prevent or treat a host of other diseases and conditions.

[Read about caffeine's role in improving performance and why sleep helps athletes.]

Quercetin is a kind of plant pigment called a flavonoid and is found naturally in red wine, apples, onions, and other foods. The potential of flavonoids in general to produce health benefits has been studied, and quercetin is no exception; it's sometimes used to treat the symptoms of prostatitis, and it's being looked at for cancer prevention, allergies, glucose absorption in diabetics, childhood asthma, and the lung disease sarcoidosis. And you can buy an energy drink, FRS, containing quercetin. But what's the evidence behind the most common claims?

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