Quercetin reduces illness but not immune perturbations after intensive exercise

Med Sci Sports Exerc. 2007 Sep;39(9):1561-9. doi: 10.1249/mss.0b013e318076b566.


Purpose: To investigate the effects of quercetin supplementation on incidence of upper respiratory tract infections (URTI) and exercise-induced changes in immune function.

Methods: Trained male cyclists (N=40) were randomized to quercetin (N=20) or placebo (N=20) groups and, under double-blind procedures, received 3 wk quercetin (1000 mg.d(-1)) or placebo before, during, and for 2 wk after a 3-d period in which subjects cycled for 3 h.d(-1) at approximately 57% Wmax. Blood and saliva samples were collected before and after each of the three exercise sessions and assayed for natural killer cell activity (NKCA), PHA-stimulated lymphocyte proliferation (PHA-LP), polymorphonuclear oxidative-burst activity (POBA), and salivary IgA output (sIgA).

Results: Pre- to postexercise changes in NKCA, PHA-LP, POBA, and sIgA did not differ significantly between quercetin and placebo groups. URTI incidence during the 2-wk postexercise period differed significantly between groups (quercetin=1/20 vs placebo=9/20, Kaplan-Meier analysis statistic=8.31, P=0.004).

Conclusion: Quercetin versus placebo ingestion did not alter exercise-induced changes in several measures of immune function, but it significantly reduced URTI incidence in cyclists during the 2-wk period after intensified exercise.

Publication types

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

MeSH terms

  • Adult
  • Antioxidants / metabolism
  • Antioxidants / pharmacology*
  • Exercise / physiology*
  • Humans
  • Immune System / drug effects*
  • Immune System / physiology
  • Killer Cells, Natural
  • Male
  • Neutrophils
  • Peroxidase / blood
  • Physical Exertion / physiology*
  • Quercetin / immunology
  • Quercetin / metabolism
  • Quercetin / pharmacology*
  • Respiratory Tract Infections / drug therapy*
  • T-Lymphocytes


  • Antioxidants
  • Quercetin
  • Peroxidase