Effect of Flavonoids on Upper Respiratory Tract Infections and Immune Function: A Systematic Review and Meta-Analysis

Abstract

Previous research on animals indicates flavonoid compounds have immunomodulatory properties; however, human research remains inconclusive. The aim of this systematic review was to assess the efficacy of dietary flavonoids on upper respiratory tract infections (URTIs) and immune function in healthy adults. A created search strategy was run against Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE and EMBASE classic, CINAHL, and AMED. The returned studies were initially screened, and 2 reviewers independently assessed the remaining studies for eligibility against prespecified criteria. Fourteen studies, of 387 initially identified, were included in this review, and the primary outcome measure was the effect of flavonoids on URTI incidence, duration, and severity. Of the included studies, flavonoid supplementation ranged from 0.2 to 1.2 g/d. Overall, flavonoid supplementation decreased URTI incidence by 33% (95% CI: 31%, 36%) compared with control, with no apparent adverse effects. Sick-day count was decreased by 40% with flavonoid supplementation, although unclear. Differences in bio-immune markers (e.g., interleukin-6, tumor necrosis factor-α, interferon-γ, neutrophils) were trivial between the intervention and control groups during the intervention and after exercise when a postintervention exercise bout was included. These findings suggest that flavonoids are a viable supplement to decrease URTI incidence in an otherwise healthy population.

Effects of 4‐Week Intervention with Ulmus macrocarpa Hance Extract on Immune Function Biomarkers in Healthy Adults: A Randomized Controlled Trial

“…Although several studies have examined the effects of dietary supplements on immune function in man [ 9 , 10 ], few have evaluated relationships between medicinal plants and immune function in human subjects. A recent systematic review and meta-analysis demonstrated the beneficial effects of plant flavonoids on upper respiratory tract infections and immune function [ 11 ]. Another clinical trial reported that the water extract of the roots of Eurycoma Longifolia favorably influenced immune parameters, such as total T cell, CD4 + T cell, and naïve T cell counts [ 12 ].…”

The impact of asthma, toll-like receptors 7 and 8, genetic and clinical determinants on antiviral immune response

“…Obesity is associated with systemic inflammation and oxidative stress and one explanation is poor diet (Manna & Jain 2015;Osadnik et al 2019). Meta-analyses show that vitamin D supplementation, antioxidant flavonoid intake and probiotics decrease the incidence of respiratory infections, which supports our findings that vitamin availability and oxidative stress affect antiviral immunity (Martineau et al 2017;Quick 2015;Somerville, Braakhuis & Hopkins 2016). A diet high in antioxidants may benefit antiviral immunity, and additionally, limited data show that it could alleviate asthma symptoms (Wood et al 2008).…”

Sports Health During the SARS-Cov-2 Pandemic

“…Regarding individual athletes, the risk of developing Covid-19 can be reduced by regular sleep, eating a wellbalanced diet, and staying well hydrated, to maintain the capacity of the immune system [28]. A proper intake of fruit and vegetables (7-8 portions per day) is beneficial, since these foods contain polyphenols and flavonoids that support immune function [29]. Athletes with asthma should use their prescribed medications meticulously to reduce the risk for a more serious course of illness.…”