Quercetin is a flavonoid that is found naturally in a variety of foodstuffs including tea, onions, apples, peppers, blueberries and dark green vegetables (Chun et al. 2007). Flavonoids are well documented to have potential antioxidant effects as well as beneficial modulatory effects on immune function.
From an exercise perspective, accumulating data in the last decade have indeed demonstrated positive physiological effects of quercetin supplementation on aiding components of training adaptation and reducing symptoms of illness during intensive periods of training. For example, double blind studies have demonstrated that 3 weeks of quercetin supplementation (1 g/day) prior to a 3 day intensive winter cycling training block reduced the incidence of upper respiratory tract infections in the subsequent 2 week recovery period (Nieman et al. 2007).
Additionally, 2 weeks of quercetin supplementation has also been shown to improve endurance running capacity, an effect potentially mediated via increased mitochondrial content of skeletal muscle (Nieman et al. 2010). Furthermore, when quercetin is co-ingested with green tea extract and fish oil supplementation, post-exercise inflammation is reduced and markers of immune function are improved in trained cyclists (Nieman et al. 2009).
When consumed in supplement form, supplementation of quercetin is deemed medically safe and does not cause any adverse symptoms or harmful physiological effects. Consumption of quercetin with green tea extract has also been shown to enhance bioavailability thus potentially exacerbating its beneficial effects. It is recommended that daily quercetin supplementation is commenced at least 7-14 days prior to the competitive event or intensive training period.
Chun O. K, Chung S. J, Song W. O. Estimated dietary flavonoid intake and major food sources of U.S. adults. J Nutr. 2007;137(5):1244–52.
Nieman D. C, Henson D. A, Gross S. J. et al. Quercetin reduces illness but not immune perturbations after intensive exercise. Med Sci Sports Exerc. 2007;39(9):1561–9.
Nieman D. C, Williams A. S, Shanely R. A. et al. Quercetin’s influence on exercise performance and muscle mitochondrial biogenesis. Med Sci Sports Exerc. 2010b;42(2):338–45.
Nieman et al. 2009. Effects of quercetin and EGCG on mitochondrial biogenesis and immunity. Med Sci Sports Exerc.41(2), 1467-1475.