The Effects of Quercetin Supplementation on Endothelial Function, Oxidative Stress, Athletic Performance, Inflammatory Biomarkers and Muscle Damage Indices in Athletes

During recent decades, a strong tendency to consume supplements in order to enhance muscular power and exercise endurance has grown among athletes. Quercetin is one of the flavonoid substances that received great attention due to its known benefits to health. The purpose of this study was to determine the effects of quercetin supplement intake on the above mentioned variables. An online search has been performed using the keywords "quercetin, endothelial function, oxidative stress, performance, inflammation, muscle damage and athletes" in ISI, Scopus and PubMed journals published during 1997-2011. All clinical trials were included in this study. A number of studies have suggested the positive effects of quercetin intake on exercise performance in athletes. These studies suggested quercetin to increase the muscle's mitochondrial biogenesis by boosting VO2max and thus delay fatigue during exercise. In addition, it did not allow NADPH oxidase, activated eNOS, augmented nitrate oxide and decreased endothelin-1 concentration, and resulted in an improvement of endothelial function. However, some other did not confirm the significant improvement of oxidative status. Most of the studies have acknowledged the positive effects of quercetin supplement intake in untrained athletes. However, due to the small number of investigations conducted on humans and the contradictory results, more controlled clinical trials are needed.