title: 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.
authors.affiliation: Department of Nutrition and Dietetics, Faculty of Medical and Health Science, The University of Auckland, Auckland, New Zealand; and vsom721@aucklanduni.ac.nz.
authors.forename: Vaughan S
authors.identifier: 0000-0002-1980-4135
authors.initials: VS
authors.lastname: Somerville
authors.affiliation: Department of Nutrition and Dietetics, Faculty of Medical and Health Science, The University of Auckland, Auckland, New Zealand; and.
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Braakhuis
authors.affiliation: College of Sport and Exercise Science, Victoria University, Melbourne, Australia.
authors.forename: Will G
authors.initials: WG
authors.lastname: Hopkins
mesh_terms: D016207:Cytokines / Q000378:metabolism; D019587:Dietary Supplements; D005260:Female; D005419:Flavonoids / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D007109:Immunity / Q000187:drug effects*; D008297:Male; D009504:Neutrophils; D008517:Phytotherapy; D010936:Plant Extracts / Q000494:pharmacology / Q000627:therapeutic use*; D012141:Respiratory Tract Infections / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism / Q000517:prevention & control
chemical_list: D016207:Cytokines; D005419:Flavonoids; D010936:Plant Extracts
keywords: common cold; exercise; flavonoids; immune function; meta-analysis; polyphenols; quercetin; systematic review; upper respiratory tract infection