Quercetin Studied for Its Immune-Boosting Effects

I have long used quercetin to stop inflammatory processes and for long-term relief of allergies. It is remarkable in that it produces no side effects and is absolutely safe. For respiratory allergies it takes 1 to 2 weeks for it's full effects to take place. Onions have high quercetin content so be sure to include them in your diet during "allergy season". An interestint point to make is it works so well that the OTC drug NasalCrom is made from quercetin. I recommend by-passing the drug and take the safer, less expensive supplemental form. I usually prescribed 1 to 2 grams (1,000mg - 2,000mg) and day in divided doses for my patients.

The following is a new study of yet another use for this special flavonoid. It has immune-boosting effects.

In a new study, quercetin was able to significantly strengthen immunity in animals exposed to the flu virus, consistent with the results of a human study released last year where the flavonoid had similar immune-enhancing effects.
Past studies have linked exercise stress to an increased risk for influenza. The flavonoid quercetin also has been reported to inhibit infectivity and replication of a broad spectrum of viruses and may offset the increase in susceptibility to infection associated with stressful exercise.

To further investigate quercetin’s possible anti-viral activities, researchers examined the flavonoid’s effects in mice that underwent stressful exercise then were exposed to influenza virus. The animals were assigned to one of four groups: exercise-placebo, exercise-quercetin, control-placebo, or control-quercetin. The exercise consisted of having the mice run until they were fatigued (approximately 140 min) on a treadmill for three consecutive days.
Quercetin (12.5 mg/kg) was administered through a stomach tube for 7 days before the mice were exposed to the virus. At 30 minutes after the last bout of exercise or rest, mice were intranasally inoculated with influenza virus. Mice were monitored daily for morbidity (time to sickness), symptom severity, and mortality (time to death) for 21 days.

Exercise stress was associated with an increased susceptibility to infection (morbidity, mortality, and symptom severity on days 5-7). However, quercetin made the animals less susceptible to viral infection after stressful exercise. The exercised mice not fed the quercetin experienced an increased susceptibility to infection of 91 percent, while quercetin was found to offset infection risk by 63 percent.

The illness rate in the mice that exercised and took quercetin was approximately equivalent to those that did not exercise, suggesting that quercetin supplementation stopped the immunity-lowering effects of the intense exercise.

According to the researchers, “These data suggest that short-term quercetin feedings may prove to be an effective strategy to lessen the impact of stressful exercise on susceptibility to respiratory infection.”

This study builds on an earlier human study where quercetin reduced illness and maintained mental performance in physically stressed subjects. Trained cyclists consumed 1,000 mg per day of quercetin (plus niacin and vitamin C) for five weeks. Another group of 20 cyclists were given a placebo. After three weeks, subjects rode a bicycle three hours per day for three days to the point of exhaustion.

After the exercise period, approximately 45 percent of the placebo-consuming cyclists became ill, while only 5 percent of the quercetin group suffered any illness. Furthermore, when given an alertness test, the quercetin-consuming subjects better maintained their ability to react after exhaustion. (Nieman DC, et. al. Research presented at the Southeastern Regional Meeting of the American College of Sports Medicine, Charlotte, N.C., February 9, 2007.)

Reference:
Davis JM, Murphy EA, McClellan JL, Carmichael MD, Gangemi JD. Quercetin reduces susceptibility to influenza infection following stressful exercise. Am J Physiol Regul Integr Comp Physiol. 2008 Aug;295(2):R505-9.