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By Daniel Gastelu Section 3. Quercetin Quercetin is one of the most common bioflavonoids found in the human diet. Because of its abundance, it's also one of the bioflavonoids that has received much attention from researchers. Due to this attention, quercetin is commonly found in dietary supplement formulas and often cited in books and articles about bioflavonoids. As a result of its varied therapeutic effects, quercetin is used by many naturopathic physicians and other natural health-care practitioners. Q. What is quercetin, and what are its health benefits? A. Quercetin, a bioflavonoid that is found in a variety of fruits and vegetables, belongs to the subclass flavonol. Researchers have identified several potential uses for this bioflavonoid, which include the treatment of atherosclerosis, cataracts, diabetes, hay fever, allergies, high cholesterol, peptic ulcers, and asthma. You should note, however, that most of the research on quercetin is either based on findings from epidemiological, or population, studies or in vitro laboratory studies-experiments that take place in a test tube. Q. What are quercetin's general uses? A. In supplemental form, quercetin's primary use is for the relief of allergies and inflammation. In scientific experiments, this bioflavonoid was found to be an effective inhibitor of histamine release from mast cells-the cause of the characteristic allergic reaction. This effect has been observed using animal and human cells in vitro. Quercetin has also been shown to inhibit the pro-inflammatory arachidonic acid metabolites-meaning that it works to prevent inflammation. Quercetin is often used with other nutrient therapies. For instance, the natural enzyme bromelain is a common ingredient in quercetin formulas designed for anti-inflammatory use. According to a naturopathic physician who is involved with a manufacturer of a form of quercetin known as quercetin chalcone, many health-care practitioners successfully use this supplement for the management of allergies. He also reported the effective use of quercetin chalcone for reducing inflammation of tissues. Q. What other clinical uses does quercetin have? A. Quercetin supplements appear to have some beneficial effects as part of supportive medical therapy for peptic ulcers. Apparently, many peptic ulcers can be caused by an infectious bacteria, known as Heliobacter pylori. Quercetin has been shown to inhibit the growth of this bacteria in in-vitro studies. Because of its anti-inflammatory action, quercetin is sometimes used as part of ulcer treatment therapy. However, ulcers should only be treated under the supervision of a health-care practitioner. If you have an ulcer, mention quercetin to your health-care professional. Q. Does quercetin have an effect on cardiovascular disease? A. Epidemiological studies conclude that higher dietary bioflavonoid intake results in a lower risk of developing diseases such as cardiovascular disease. The Hertog epidemiological study discussed in section 1 reported that quercetin and other bioflavonoids may help reduce the risk of strokes. This can be especially useful for people who have a family history of stroke and cardiovascular disease. As quercetin is one of the most prevalent dietary bioflavonoids, researchers speculate that it, like other bioflavonoids, has beneficial effects on the cardiovascular system by inhibiting platelet aggregation through its antioxidant activity. Although research has determined that quercetin does reduce human blood-platelet aggregation, clinical studies are needed to confirm a cause and effect relationship between quercetin ingestion and platelet aggregation inhibition. Q. How can quercetin help people with diabetes? A. Quercetin has been found to be an inhibitor of the enzyme aldose reductase, which plays a role in converting glucose (sugar) to sorbitol (a sugar alcohol) in the body. Sorbitol buildup in the body is one way people with diabetes develop secondary problems, such as neuropathy, retinopathy, diabetic cataracts, and nephropathy. Quercetin may therefore be beneficial in the nutritional management of diabetes, but clinical studies need to be conducted to verify these effects, which have been observed in non-human experiments. Q. How safe is quercetin? A. As already mentioned, quercetin is a major bioflavonoid found in diets all over the world. Moreover, diets that are high in bioflavonoids are associated with a lower incidence of many diseases, most notably cancer and coronary heart disease. In addition, quercetin has been shown to exert anti-carcinogenic effects in many in vitro studies. However, back in the 1970s, quercetin was found to have mutagenic activity as determined by the in vitro Ames test, which was developed by researcher Bruce Ames to test if a natural or synthetic substance will cause DNA mutations in bacteria. This prompted toxicologists and nutritionists to conduct more research to answer the safety question of quercetin. In subsequent animal studies, diets containing 0.1 and 0.2 percent of quercetin were found to increase the incidence of bladder tumors in rodents. However, out of the many studies that have followed, none have shown that quercetin has a mutagenic or carcinogenic effect in humans in the amount usually found in the human diet. Long-term animal studies actually found that quercetin might exert an anti-carcinogenic effect as reported by B. Stavic of the Canadian Health & Protection Department. As more studies were undertaken to determine the biological effects of quercetin, researchers found-mostly in in vitro and animal studies-a wide range of potential beneficial biological properties, including anti-microbial, inhibition of tumor promotion by chemical carcinogens, anti-thrombosis, inhibition of disease-promoting enzymes, anti-allergenic, anti-inflammatory, and inhibition of platelet aggregation activities. It's also interesting to note that many herbal products, such as ginkgo and hawthorn, contain quercetin. Based on our current understanding of quercetin in the human diet, it does not appear to induce health problems. Quercetin may actually contribute toward the reduction of disease risks. Q. Exactly what is quercetin chalcone? A. Quercetin chalcone is a non-toxic form of quercetin as determined by the Ames test and animal studies. It was developed by Thorne Research, Inc., to allay concerns over possible side effects of quercetin. While there has not been any cause-effect relationship established that proves quercetin intake from food or supplements causes harmful effects in humans, it is best to take quercetin chalcone if you decide to take quercetin in high doses for extended periods. The manufacturer reported that quercetin chalcone has been used by naturopathic physicians on thousands of patients without observing any adverse effects. Quercetin chalcone is also more bioavailable than quercetin, which means it may be better absorbed and used by the body, but clinical research studies are required to confirm this speculation. Q. How much quercetin or quercetin chalcone should I take? A. The average diet can supply 15 to 40mg of quercetin per day from fruit and vegetable consumption. Increasing quercetin intake for general health reasons can be accomplished by simply eating more vegetables and fruit. However, as most people are confronted with the reality of not being able to maintain an adequate intake of bioflavonoids from food sources, extra quercetin can be obtained from dietary supplements. There are many all-in-one supplements that contain vitamins, minerals, quercetin, and other bioflavonoids and nutrients. For therapeutic purposes-for example, for allergy management, anti-inflammatory treatment, and disease treatment-higher dosages of quercetin are usually prescribed by health-care practitioners. Therapeutic dosages can range from 250 to 500mg three times per day. The higher amounts are needed to raise quercetin in the body to therapeutic levels. To insure safe use, it is recommended that you use high dosage only for short periods of time, and under the supervision of a health-care practitioner.
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