The August 1, 2008 issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology reported the details of a study conducted by researchers at the University of South Carolina and Clemson University which found that quercetin, a compound that occurs in many fruits and vegetables, helped protect against influenza in mice exposed to the virus.
In the current study, conducted by J. Mark Davis of the University of South Carolina’s Arnold School of Public Health and colleagues, one group of mice was given quercetin for seven days while the remainder received no quercetin. Half of the mice in each group were exercised to fatigue on the last three days of the treatment period. One half hour following the final exercise session, the animals were inoculated with an influenza A strain, and were monitored for signs of illness for 21 days.
Mice that experienced exercise-related stress demonstrated a greater susceptibility to influenza. Ninety-one percent of these mice developed signs of the flu, compared with 63 percent of nonexercising animals. Mice that exercised to fatigue also exhibited signs of the flu earlier than other animals that developed influenza. Among those that received quercetin, however, the same rate of influenza occurred as in mice that did not exercise, demonstrating that the compound cancelled the temporary stress-related depression of immune function caused by intense exercise. Mice that did not engage in intense exercise also experienced a protective benefit from quercetin.
Quercetin, found in grapes, tea, blueberries, and other foods, is chemically related to resveratrol, a compound that has also been shown to have some antiviral benefits in laboratory studies. “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,” Dr Davis commented.
In previous research with quercetin, reported in the February 13, 2007 issue of Life Extension Update, athletes who received quercetin for five weeks experienced fewer viral illnesses following exercise-induced stress compared with those given a placebo.
“This is the first controlled experimental study to show a benefit of short-term quercetin feedings on susceptibility to respiratory infection following exercise stress,” Dr Davis announced. “Quercetin feeding was an effective preventive strategy to offset the increase in susceptibility to infection that was associated with stressful exercise.”