Quercetin reduces susceptibility to influenza, especially after exercise
A new scientific study offers good news for both athletes and wine fans. Researchers at the University of South Carolina say a chemical found abundantly in red wine, apples and onions helps protect against influenza, especially after a rigorous respiratory workout when the body is more susceptible to infection.
The chemical, quercetin, is a known anti-inflammatory found in the skins of fruit and vegetables. Prior studies have theorized that it helps reduce lung inflammation and inhibits the growth of prostate cancer.
According to the new study, published in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology, strenuous exercise is widely believed to increase susceptibility to the flu, due to the stress that a high level of activity places on the body. Researchers at the university’s department of exercise science, which focuses on the alleviation of exercise-related ailments, wanted to see if exercise increased the chances of catching the flu and if quercetin could reduce those chances.
According to J. Mark Davis, director of the exercise biochemistry lab and study lead author, «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.»
The team separated approximately 100 mice into four groups. Two groups were served water while the other two were served Tang treated with 12.5 milligrams per kilogram of quercetin. (The USDA states that the average red table wine contains 8.4 mg/kg of quercetin—unpeeled red apples average 44.2 mg/kg of quercetin and cooked red onions contain 193.3 mg/kg.)
One water group and one quercetin group were exercised on a treadmill to the point of exhaustion without injury over the course of three days. Afterward, the scientists infected all the mice with the influenza virus and tracked the disease’s progress. They found that the mice that were not given quercetin but were exercised were more likely to develop flu symptoms. Of those, 91 percent fell ill, compared to 63 percent of the water-fed rodents that weren’t exercised.
The rate and severity of infection among mice that were served quercetin and exercised was similar to the non-exercising, non-quercetin mice. Perhaps more importantly, the number of mice that eventually died from infection was comparatively lower among the quercetin groups.
«This is the first controlled experimental study to show a benefit of short-term quercetin feedings on susceptibility to respiratory infection following exercise stress,» said Davis. «Quercetin feeding was an effective preventive strategy to offset the increase in susceptibility to infection that was associated with stressful exercise.»
The study notes that the anti-viral properties of quercetin remain unknown, but it speculates that the compound may block the ability of the virus to replicate itself. Davis adds, however, that he isn’t positive that humans would see a similar benefit. But he believes the research may help endurance athletes, soldiers and others who encounter physically challenging circumstances.
The South Carolina study is not the only recent research to highlight quercetin. In the March 2008 issue of Atherosclerosis, a study conducted by the Institute of Food Research in England found that the compound reduces inflammation associated with cardiovascular disease. Athletic interest in the power of quercetin is also gaining speed. Last year cycling great Lance Armstrong, who announced just this week plans to come out of retirement, joined the board of directors of New Sun Nutrition, which markets a sports drink called FRS that contains the compound. «Quercetin is our secret weapon against fatigue,» the company claims.