Post-160-km race illness rates and decreases in granulocyte respiratory burst and salivary IgA output are not countered by quercetin ingestion

Int J Sports Med. 2008 Oct;29(10):856-63. doi: 10.1055/s-2007-989424. Epub 2008 Jan 22.


This study measured the influence of the flavonoid quercetin on immune changes and incidence rates of upper respiratory tract infections in ultramarathoners competing in the 160-km Western States Endurance Run. Sixty-three runners were randomized to quercetin and placebo groups, and under double-blinded methods ingested 1000 mg/day quercetin for 3 wks before, during, and 2 wks after the race. Thirty-nine of the 63 subjects (n = 18 for quercetin, n = 21 for placebo) finished the race and provided blood and saliva samples the morning before the race and 15 - 30 min postrace. Upper respiratory tract infections were assessed during the week before and the 2-wk period after the race using an illness symptom checklist. Race times did not differ significantly between quercetin and placebo groups. Significant pre- to postrace decreases were measured for natural killer cells (43 %), granulocyte respiratory burst activity (55 %), and salivary IgA output (48 %), and increases for neutrophil (288 %) and monocyte (211 %) cell counts, with no significant group differences. Postrace illness rates did not differ between groups. In conclusion, quercetin supplementation for 3 wks before and 2 wks after the Western States Endurance Run had no effect on illness rates, perturbations in leukocyte subset counts, or decreases in granulocyte respiratory burst activity and salivary IgA.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Antioxidants / administration & dosage
  • Antioxidants / pharmacology*
  • Antioxidants / therapeutic use
  • Female
  • Granulocytes / drug effects*
  • Granulocytes / physiology
  • Humans
  • Immunoglobulin A / analysis*
  • Male
  • Middle Aged
  • Quercetin / administration & dosage
  • Quercetin / pharmacology*
  • Quercetin / therapeutic use
  • Respiratory Burst / drug effects*
  • Respiratory Burst / physiology
  • Respiratory Tract Infections / epidemiology
  • Respiratory Tract Infections / immunology
  • Respiratory Tract Infections / prevention & control*
  • Running / physiology
  • Salivary Glands / metabolism
  • Sports


  • Antioxidants
  • Immunoglobulin A
  • Quercetin