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 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 also shows anti-tumour properties. A study in the British Journal of Cancer showed 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.
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 and other leafy green vegetables, cherries, and a number of berries including raspberry, bog whortleberry (158 mg/kg, fresh weight), lingonberry (cultivated 74mg/kg, wild 146 mg/kg), cranberry (cultivated 83 mg/kg, wild 121 mg/kg), chokeberry (89 mg/kg), sweet rowan (85 mg/kg), rowanberry (63 mg/kg), sea buckthorn berry (62 mg/kg), crowberry (cultivated 53mg/kg, wild 56 mg/kg), and the fruit of the prickly pear cactus. A recent study found that organically grown tomatoes had 79% more quercetin than conventionally grown.
In plants, it is a naturally-occurring polar auxin transport inhibitor.
- "Induction of cancer-specific cytotoxicity towards human prostate and skin cells using quercetin and ultrasound". British Journal of Cancer. 92 (3): 499–502. 2005. doi:10.1038/sj.bjc.6602364. Retrieved 2007-5-19. Check date values in:
- USDA Database for the Flavonoid Content of Selected Foods
- Crystal Smith, Kevin A. Lombard, Ellen B. Peffley, Weixin Liu (2003). "Genetic Analysis of Quercetin in Onion (Allium cepa L.) Lady Raider" (PDF). The Texas Journal of Agriculture and Natural Resource. Agriculture Consortium of Texas. 16: 24–28. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
- Sari H. Häkkinen; et al. (1999). "Content of the Flavonols Quercetin, Myricetin, and Kaempferol in 25 Edible Berries". Journal of Agricultural and Food Chemistry. ACS Publications. 47 (6): 2274–2279. doi:10.1021/jf9811065 S0021-8561(98)01106-6 Check
|doi=value (help). PMID 10794622. Retrieved 2007-06-13. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
- "Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes"
- Honey Research Unit
- honey fingerprinting
- Shoskes, DA; et al. (1999). "Quercetin in men with category III chronic prostatitis: a preliminary prospective, double-blind, placebo-controlled trial". Urology. 54 (6): 960-3. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
- UMM Quercetin Info Page (University of Maryland Medical Center Website)
- Eyes right for a cup of tea UK Institute of Food Research article on how quercetin can help prevent cataracts.
- Plant foods for health protection article by the Institute of Food Research (Norwich, United Kingdom)
- Scanning Electron Micrograph image of quercetin crystals derived from onion
- Possible Interactions with: Quercetin Quercetin might enhance the effects of two chemotherapy medications
- Quercetin Info from the Cedars-Sinai Medical Center, Los Angeles.
- "Genetic Analysis of Quercetin in Onion (Allium cepa L.)" article from The Texas Journal of Agriculture and Natural Resource 16:24-28 (2003).
- "Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes" article at American Chemical Society website (originally published 23rd June 2007).
- "An apple a day could help protect against brain-cell damage" article at Cornell University website (originally published 2nd December 2004).