Abstract
This is a review of recent human clinical trials evaluating quercetin supplementation at doses of 1,000 mg/day. A recent study suggests supplementation with quercetin combined with fish oil and green tea extracts yields greater effect than quercetin alone. Some studies on athletic performance suggest moderate effect in trained athletes and more significant effect in untrained individuals. Both animal and human data suggest quercetin stimulates mitochondrial biogenesis. The scientific literature provides compelling clinical information about this interesting flavonol.
Introduction
A series of interesting and closely related studies published over the last year describe the effects of quercetin on endurance athletes and their performance. These studies provide knowledge that should inform our practices and should change the way we dose quercetin and broaden the range of situations in which we consider using this supplement.
Epidemiological studies suggest that quercetin should be of benefit in preventing a range of different diseases. Although some mouse studies bear these predictions out, human trials have demonstrated little benefit. Individuals who participate in extreme endurance sports produce distinct inflammatory and oxidative stresses in their bodies as well as disruptions in immune function. Studying the effect of quercetin on these athletes provides a means to test quercetin’s long-term predicted effects over the short term and to experiment with varying methods of dosing, compounding, and combinations with other nutrients to enhance quercetin’s effectiveness.
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Quercetin is classified as a flavonol, 1 of the 5 subgroups of flavonoid compounds. Flavonoids in turn are a subgroup of the polyphenolic subgroup of the phenolic organic compounds found in plants. Food sources of quercetin include elderberries (42 mg/100 grams), red onions (33 mg/100 grams), hot peppers (15 mg/100 grams), apples (4.7 mg/100 grams), and kale (7.7 mg/100 grams). Capers contain far greater amounts (180 mg/100 grams) but are rarely consumed in significant quantity. The 1,000 mg/day dose of quercetin used in these recent trials far exceeds the amount of quercetin that would be easily consumed via diet.
In vitro animal and human epidemiologic studies suggest a long list of desirable effects result from consuming quercetin in the diet. These include antioxidative, anti-inflammatory, antibacterial, immunomodulatory, anticarcinogenic, and cardioprotective actions. High quercetin intake via diet is associated with decreased rates of colorectal, kidney, pancreatic, prostate, and lung cancer; cardiovascular disease; and diabetes.
Many of these protective effects are hypothetically considered to be a result of quercetin’s antioxidative and anti-inflammatory actions. The extreme exercise engaged in by certain athletes, because it causes oxidative damage and inflammatory reactions, has been used to test quercetin’s potential protective effects. Extreme exercise in theory mimics the effect of aging, trauma, and surgery. A treatment that benefits these athletes might also prevent or help treat diseases and morbidity caused by oxidative damage and inflammation.