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Quercetin is a flavonoid and more specifically a flavonol. It is the aglycone form of a number of other flavonoid glycosides, such as rutin and quercitrin found in citrus fruit. Quercetin (see FRS Energy Products Here) is found to be the most active of the flavonoids in studies, and many medicinal plants owe much of their activity to their high quercetin content. Quercetin has demonstrated significant anti-inflammatory activity because of direct inhibition of several initial processes of inflammation. For example, it inhibits both the manufacture and release of histamine and other allergic/inflammatory mediators. In addition, it exerts potent antioxidant activity and vitamin C-sparing action.
Quercetin forms the glycosides quercitrin and rutin together with rhamnose and rutinose respectively.
Quercetin also shows remarkable anti-tumour properties. A recent study in the British Journal of Cancer shows that when treated with a combination of quercetin and ultrasound at 20 KHz for 1 minute duration, skin and prostate cancers show a 90% mortality within 48 hours with no visible mortality of normal cells. Note that ultrasound also promotes topical absorption by up to 1,000 times making the use of topical quercetin and ultrasound wands an interesting proposition.
Quercetin may have positive effects in combating or helping to prevent cancer, prostatitis, heart disease, cataracts, allergies/inflammations, and respiratory diseases such as bronchitis and asthma.
Foods rich in quercetin include capers(1800mg/kg), lovage(1700mg/kg), apples, tea (Camellia sinensis), onions (higher concentrations of quercetin occur in the outermost rings), red grapes, citrus fruits, broccoli & other leafy green vegetables, cherries, and a number of berries including raspberry, bog whortleberry (158 mg/kg, fresh weight), lingonberry (74 and 146 mg/kg), cranberry (83 and 121 mg/kg), chokeberry (89 mg/kg), sweet rowan (85 mg/kg), rowanberry (63 mg/kg), sea buckthorn berry (62 mg/kg), crowberry (53 and 56 mg/kg), and the fruit of the prickly pear cactus. A study by the University of Queensland, Australia, has also indicated the presence of quercetin in varieties of honey, including honey derived from eucalyptus and tea tree flowers.
In plants, it is a naturally-occurring polar auxin transport inhibitor.
^ (2005) "Induction of cancer-specific cytotoxicity towards human prostate and skin cells using quercetin and ultrasound". British Journal of Cancer 92 (3): 499-502. DOI:10.1038/sj.bjc.6602364. Retrieved on 2007-5-19.