There was great excitement about initial studies done on quercetin in mice demonstrating improved athletic endurance. However, studies in humans have been disappointing.
Quercetin is a phytochemical found in red, green and purple pigmented plants, including apples, red onions, tomatoes and berries. The substance is sold as a dietary supplement in isolated form. A powerful antioxidant with anti-inflammatory properties, quercetin may help to prevent cancer, especially prostate cancer.
Early studies in mice demonstrated evidence that quercetin enhanced performance in mice. In one study, two groups of mice were given either quercetin or placebo and were tested before and after administration on a wheel treadmill. The mice that received quercetin ran 37% longer that their counterparts receiving the placebo.
Several quercetin studies in human athletes and non-athletes did not produce the same results. F.R.S. financed a small study which demonstrated that highly trained human athletes improved their performance on quercetin. The subjects were then given a placebo and they also had significant improvement in performance. A second study was done using 12 untrained men who demonstrated improvement after 1 week on quercetin.
However three additional studies had disappointing results. Runners in the 100-mile Western States Endurance Run were given quercetin and saw no difference. A similar study done with cyclists by the same researchers, who found no difference in endurance levels.
The most recent study was done in 2009 by Coca-Cola, which was testing a new drink containing quercetin. In a New York Times article, lead author Kirk J. Cureton, stated: “There were simply no differences” between the quercetin and placebo groups. The professor of kinesiology at the University of Georgia added, "It just does not improve endurance."