Quercetin Counters the Effect of Stressful Exercise on Flu Susceptibility

The medically active plant flavonol quercetin has been found to counteract the effects of stressful exercise on the susceptibility of experimental mice to influenza.

Quercetin, a flavonol that is the active factor in many medicinal plants, demonstrates significant anti-inflammatory activity through direct inhibition of several initial processes of inflammation. For example, it inhibits both the manufacture and release of histamine and other allergic/inflammatory mediators. In addition, it exerts potent antioxidant activity and vitamin C-sparing action.

Quercetin also shows antitumor properties, with a combination of quercetin and ultrasound killing 90% of skin and prostate cancer cells within 48 hours with no visible mortality of normal cells. Indications from other studies suggest that quercetin may have positive effects in combating or helping to prevent prostatitis, heart disease, cataracts, allergies/inflammations, and respiratory diseases such as bronchitis and asthma. Quercetin is present in a variety of fruits and vegetables, including red onions, grapes, blueberries, tea, broccoli, and red wine.

In the current study, investigators from the University of South Carolina (Columbus, SC, USA) examined the effect of quercetin on mice exposed to influenza virus after bouts of stressful exercise, which renders the animals more susceptible to infection by the virus.

Results published in the August 2008 issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology confirmed that stressful exercise increased susceptibility of the mice to the flu. Mice that exercised to fatigue for three days were more likely to develop the flu than the mice that did not exercise (91% versus 63%). The mice that exercised developed the flu much sooner than those mice that did not (6.9 days versus 12.4 days). Mice that exercised and then received quercetin had nearly the same rate of illness as those that did not exercise. Thus, quercetin canceled out the negative effect of stressful exercise. The severity of the symptoms among either those mice that did not exercise or those that exercised but received quercetin was about the same.

"Quercetin was used because of its documented widespread health benefits, which include antiviral activity, abundance in the diet, and reported lack of side effects when used as a dietary supplement or food additive,” said first author Dr. J. M. Davis, professor of exercise science at the University of South Carolina. "This is the first controlled experimental study to show a benefit of short-term quercetin feedings on susceptibility to respiratory infection following exercise stress. Quercetin feeding was an effective preventive strategy to offset the increase in susceptibility to infection that was associated with stressful exercise.”

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