The effect of quercetin on the prevention or treatment of COVID-19 and other respiratory tract infections in humans: A rapid review

There is currently insufficient evidence to recommend quercetin supplementation as a therapy for the treatment or prevention of COVID-19. Three human clinical trials with low risk of bias suggest that oral quercetin may have a beneficial effect on the incidence and duration of respiratory tract infections in certain populations; however, further research is needed. Current evidence on the efficacy of quercetin supplementation in the treatment and prevention of COVID-19 is insufficient for its clinical recommendation at this time. Quercetin exhibits both immunomodulatory and antimicrobial effects in preclinical studies; however, only three human clinical trials, each with a low risk of bias rating, were identified in this rapid review. One study reported a decrease in incidence of upper respiratory tract infections following a competitive athletic event. A larger community clinical trial reported a benefit in older, athletic adults only.