Effectiveness of supplementation with quercetin‐type flavonols for treatment of viral lower respiratory tract infections: Systematic review and meta‐analysis of preclinical studies

Abstract

Viral infections of the lower respiratory tract are considered a public health problem. They affect millions of people worldwide, causing thousands of deaths, and are treated with expensive medicines, such as antivirals or palliative measures. In this study, we conducted a systematic review to describe the use of quercetin‐type flavonols against lower respiratory tract viruses and discussed the preclinical impact of this approach on different signs and clinical mechanisms of infection. The systematic review was performed in PubMed/MEDLINE, Scopus, Scielo, and Biblioteca Virtual de Saúde (BVS). After the database search, 11 relevant studies were identified as eligible. The analysis of these studies showed evidence of antiviral activity of quercetin‐type flavonols with significantly reduced mortality rate (M‐H = 0.19, 95% CI: 0.05 to 0.65, p‐value = 0.008) of infected animals and a reduction in the average viral load (IV = −1.93, 95% CI: −3.54 to −0.31, p‐value = 0.02). Additionally, quercetin and its derivatives reduced the amount of proinflammatory cytokines, chemokines, reactive oxygen species, mucus production, and airway resistance in animals infected with a respiratory virus. Overall, supplementation with quercetin‐type flavonols is a promising strategy for treating viral‐induced lower respiratory tract infections.

Possible Therapeutic Effects of Adjuvant Quercetin Supplementation Against Early-Stage COVID-19 Infection: A Prospective, Randomized, Controlled, and Open-Label Study

“…Supplementing with quercetin-type molecules could therefore be considered a promising strategy for the treatment of viral respiratory infections. 30…”

Potential Clinical Benefits of Quercetin in the Early Stage of COVID-19: Results of a Second, Pilot, Randomized, Controlled and Open-Label Clinical Trial

“…20 Finally, although quercetin's precise antiviral mechanisms are not yet completely understood, there is a considerable body of evidence supporting the broad antiviral properties of quercetin, demonstrated both in in vitro and in vivo studies through inhibition of viral replication of several respiratory viruses, including influenza virus, parainfluenza virus, respiratory syncytial virus, adenovirus, and rhinovirus. 21 As for most of polyphenols, the practical use of quercetin is limited by its low solubility and reduced oral absorption. 22,23 Recently, quercetin formulated with sunflower lecithin has been demonstrated in humans to attain high plasma levels, up to 20 times greater than those usually obtained following the administration of an equal dose of unformulated quercetin, without any notable side effects.…”

Flavonoids for Treating Viral Acute Respiratory Tract Infections: A Systematic Review and Meta-Analysis of 30 Randomized Controlled Trials

“…To date, there are some studies conducted on patients concerning the efficacy of flavonoids against respiratory tract infections. Preclinical studies have shown evidence of antiviral activity of quercetin-type flavonols with a significantly reduced mortality rate of infected animals and a reduction in the average viral load ( 16 , 17 ). Furthermore, a meta-analysis in 2016 conducted by Somerville et al included 14 studies and found that flavonoid supplementation decreased upper respiratory tract infections incidence by 33% compared with control in healthy adults, with no apparent adverse effects ( 18 ).…”