Quercetin Reduced Activity-Induced Illness

G. Douglas Andersen, DC, DACBSP, CCN

For over 30 years, doctors, researchers, and scientists have noticed that following high intensity long duration competition, athletes seemed to acquire an increased susceptibility to illness in the weeks after the event. This problem received a shot of publicity in 1990 when a paper was published that showed 1 out of every 7 athletes who competed in the Los Angeles Marathon sustained an upper respiratory infection in the 2-weeks following the race. Control runners who did not compete fell ill at a 1 out of 50 rate.1

Quercetin is a polyphenolic compound classified as a flavonoid and more specifically, a flavonol. Quercetin has anti-inflammatory, antihistaminic, and anti-oxidant properties. In quercetin-containing foods, the highest levels are located in the skin, outer layers, or the leaves. This is because sunlight stimulates endogenous production.2 An 8-ounce apple contains around 100 mg of quercetin. Other foods high in quercetin include red grapes; onions (outer layers); berries; tea leaves; green, leafy vegetables; capers; citrus; hot peppers; and broccoli. The typical American adult diet provides 15-25 mg of quercetin a day.3 Quercetin is well absorbed and has a long half-life (12-24 hours).4 Quercetin has been used for various conditions including prostatitis, pancreatitis, asthma, eczema, gout, cataract, ulcers, and hives. Evidence from culture studies shows it possesses antiviral, antibacterial, and anticarcinogenic properties.5

The Study6
A group of 40 male cyclists between 25 and 30 years of age were recruited to study the effects of quercetin. The subjects’ workouts averaged 90 minutes a day and totaled between 150 and 170 miles per week. They were divided into 2 groups of 20. Each group mixed 8 ounces of water to a pre-measured amount of an orange flavored beverage (Tang) and consumed two servings daily (before breakfast and after dinner). The intervention groups’ mixture contained 500 mg of quercetin in each serving. The subjects stopped using all nutritional supplements except for the drink for a 3-week period while maintaining their normal diets and workouts. They then underwent 3 consecutive days of supervised 3-hour test rides which doubled their normal amount of exercise. Following the test, the subjects continued to use the beverages twice daily for an additional 2 weeks and resumed their regular workout schedule.

There were no differences between groups for blood lymphocytes, granulocytes, leukocytes, leukocyte subsets, and NK cell levels. Plasma cortisol, epinephrine, norepinephrine, and myeloperoxidase were measured with the same result--no differences between placebo and quercetin. Salivary IgA was also measured. Again, there were no differences between groups.

Post Study Questionnaire
The results for both the control and placebo groups were exactly the same. In each group, 9 subjects thought they were taking quercetin, 4 subjects thought they were taking placebo, and 7 subjects were unsure.

Upper Respiratory Infection
There were no differences between groups in the 3 weeks leading up to the protocol. In the 2 weeks following the 3 day test, 1/20 subject in the quercetin group contracted an upper respiratory infection while 9/20 placebo subjects got ill.

Clearly, this study is limited by the small number of subjects. Nevertheless, the results were quite impressive. It will be interesting to see if they can be reproduced. And, if they are, it will be very interesting to see how quercetin assists immunity without affecting any of the biomarkers measured in this study.

1 Neiman, D.C., Johanssen, L.M., Lee, J.W, and Aradatzis, K. Infectious Episodes in Runners Before and After the Los Angeles Marathon. Journal of Sports Medicine and Physical Fitness. 1990; 30: 316-328.
2 Manach, C., Scalbert, A., Morand, C. et. al., Polyphenols: Food Sources and Bioavailability. Am J Clin Nutr: 2004;79:727-747.
3 Sampson, L., Rinn, E., Hollman, P.C., et. al. Flavonol and Flavone Intakes in US Health Professionals. J. Am. Diet. Assoc.: 2002;102:1414-1420.
4 Erlund, I.,Freese, R., Marnieni, J., et al. Bioavailability of Quercetin from Berries and the Diet. Nutr Cancer: 2006;54:13-17.
5 Cuxhnie, T.P., Lamb, A.J. Antimicrobial Activity of Flavonoids. Int J Antimicrob Agents. 2005; 26:343-356.
6 Nieman, D.C., Henson, D.A.,Gross S.J., et al. Quercetin Reduces Illness But Not Immune Perturbations After Intensive Exercise. Med Sci Sports Exercise. 2007; 39:1561-1569.


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