Quercetin is a flavonol, one of a class of bioflavonoids found in fruits, vegetables, leafy greens and grains. Plants produce these chemical compounds to protect themselves against parasites, bacteria and cell injury and to preserve vitamins. Apple skins, tea, red wine and onions are particularly high in quercetin, which may have beneficial effects on human health.
Cancer Prevention
Animal studies and research investigating the causes of cancer have demonstrated that quercetin's effects may reduce the rate of some colon and lung cancers. These were the findings of A. Murakami and colleagues from Kyoto University in Japan. Quercetin seems to have the ability to calm inflammation associated with processes that lead to cancer. The report was published in the October 2008 "Cancer Letters." The American Cancer Society reports that some studies suggest quercetin inhibits the growth of cancer cells, but that more conclusive clinical trials are needed before supplements can be recommended as an addition to cancer treatment. A high dietary intake of vegetables and fruits is associated with a lower risk of developing malignancies.
Antioxidant Effects
Quercetin enhances the resistance of cell membranes against destruction by free radicals, according to a study by the Department of Military and Emergency Medicine in Bethesda, Maryland. Free radicals are atoms that contain unpaired electrons, which can easily bond with other atoms or molecules, causing oxidative damage and degenerative changes. These particularly affect the heart muscle, nerve cells and immune factors. Things that contribute to the proliferation of free radicals include radiation exposure, smoking, air pollution and a diet high in fried foods. C.D. Hapner and colleagues published the report in the August 2010 issue of "Chemico-Biological Interactions."
Reduced Muscle Fatigue
The role of quercetin in exercise physiology is being explored. Intriguing animal studies have demonstrated dramatically enhanced muscle endurance after treatment with quercetin, possibly due to stimulation of the growth of mitochondria, which are energy-producing powerhouses in cells. Low levels mitochondria are associated with aging, and higher amounts are found in conditioned athletes. In a randomized, controlled, double-blind, cross-over study, 12 healthy but untrained volunteers were given either a quercetin fortified drink or placebo for two periods of seven days each. J. M. Davis and colleagues at the University of South Carolina measured baseline maximum oxygen intake and bike ride time to fatigue and compared assessments at study intervals. Results showed a modest increase in oxygen intake and substantially prolonged ride times among subjects who received quercetin. The findings were published in the February 2010 "International Journal of Sport Nutrition and Exercise Metabolism." In a New York Times Health article published in October 2009, Gretchen Reynolds describes earlier results of studies assessing the effects of quercetin in trained athletes as "disappointing." Reynolds suggests the possibility that study subjects in peak condition may also have reached a pinnacle of mitochondrial proliferation.
References
- Pubmed.gov: Multitargeted Cancer Prevention by Quercetin
- ACS: Quercetin
- Pubmed.gov: Inhibitions of Oxidative Hemolysis by Quercetin, but Not Other Antioxidants
- Pubmed.gov: The Dietary Flavonoid Quercetin Increases VO2 Max and Endurance Capacity
- N.Y. Times: Phys Ed, Is Quercetin Really a Wonder Sports Supplement?, Gretchen Reynolds, Oct. 7, 2009
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