Severe exercise training has been shown to affect the immune system, thereby influencing the body’s susceptibility to infection. More specifically, exercise stress has been hypothesized to increase the risk of acquiring an upper respiratory tract infection. Many studies have attempted to find a nutritional strategy to counter-act this increased risk. Supplementation with quercetin is one of these strategies. Quercetin is a flavonoid present in a wide variety of fruits and vegetables, and it has been shown to have anti-viral activity in vitro. This makes it a promising candidate for helping reduce the risk of influenza infection following stressful exercise.
A recent study on mice examined querectin’s effectiveness in this regard. Mice were divided into four groups: exercise-quercetin, exercise-placebo, no exercise-quercetin and no exercise-placebo. Mice in the exercise groups were run on a treadmill for a prolonged period of time for three consecutive days. Quercetin supplementation was given for seven days prior to infection. Mice in all four groups were inoculated with the influenza virus following the third period of exercise.
After inoculation, the mice were examined for signs of influenza infection. The exercise-placebo group showed a very high incidence of severe infection (91%) as compared to the no exercise-placebo group (63%). This showed that exercise training does indeed increase the risk and severity of infection. Supplementation with quercetin, however, effectively counter-acted this effect, with mice in the exercise-quercetin group showing a similar infection rate (67%) to the groups that were not exercised.
Although this study was performed in mice, there is evidence that quercetin can have similar effects in humans. One study on athletes showed that supplementation with quercetin reduced the rate of upper respiratory tract infections following three days of intense cycling. While the study was not strictly controlled, its results are well supported by the results in mice. These results are very promising and show that short-term supplementation with quercetin could be an effective nutritional strategy for reducing the risk of upper respiratory tract infections in people often exposed to physical and environmental stress, like athletes and military personnel.
Davis JM, Murphy EA, McClellan JL, Carmichael MD, Gangemi JD. 2008. Quercetin reduces susceptibility to influenza infection following stressful exercise. Am J Physiol Regul Integr Comp Physiol 295: R505-R509.
For more information, see Quercetin.
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