More quercetin: a (tiny) endurance boost

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Last fall, an excellent University of Georgia study failed to confirm the endurance-boosting effects of the supplement quercetin that earlier mouse studies had suggested. Now there’s a new study on quercetin from David Nieman’s highly respected lab at Appalachian State University, in the February issue of Medicine & Science in Sports & Exercise — and the news is mixed.

Reading the abstract, you might conclude the double-blinded crossover study was a success: they found “a small but significant improvement in 12-minute treadmill time trial performance” after two weeks of 1,000 mg of quercetin a day. Quercetin is a flavonoid that is thought to enhance the growth of new mitochondria, which is the most significant adaptation resulting from endurance training. So they also performed muscle biopsies, but these didn’t show a significant effect (though there were “insignificant increases”).

When you read the study closely, even the treadmill improvement is a disappointing result. An earlier study from the same lab had failed to find any improvement for well-trained cyclists in 5-, 10-, and 20-km time trials. So they hypothesized that the benefits of quercetin wouldn’t show up for well-trained athletes, who already have a high density of mitochondria. This study specifically enrolled sedentary young adults: the maximal exercise level permitted was 20 minutes, twice a week.

In other words, these were subjects ripe for LARGE improvements. What they found was an improvement of 2.9% in treadmill distance, while the placebo group actually got 1.1% worse. It is statistically significant (barely: P=0.038), but it’s hard to argue that it’s practically significant. For people this sedentary, an occasional walk around the block would have done more. An improvement of a percent of two is only really significant for elite athletes — precisely who this study wasn’t aimed at.

The authors acknowledge that the effect is far smaller than that seen in mouse studies, and they conclude that further research is needed with higher doses and longer study periods. This sounds like a good idea — but until those studies come in, the logical assumption is that quercetin doesn’t offer any practical benefit for people of any fitness level.