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CAS number 117-39-5 Yes check.svgY
PubChem 5280343
Molecular formula C15H10O7
Molar mass 302.236 g/mol
Exact mass 302.042653
Density 1.799 g/cm3
Melting point

316 °C

 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Quercetin quer·ce·tin (ˈkwər-sə-tən) is a flavonol, plant-derived flavonoid, used as a nutritional supplement. Laboratory studies show it may have anti-inflammatory and antioxidant properties [1][2], and it is being investigated for a wide range of potential health benefits.[2][3]

Quercetin has been shown to increase energy expenditure in rats, but only for short periods (fewer than 8 weeks) [1]. Effects of quercetin on exercise tolerance in mice have been associated with increased mitochondrial biogenesis.[2]


Informed medical opinion

The American Cancer Society says that while quercetin "has been promoted as being effective against a wide variety of diseases, including cancer," and "some early lab results appear promising, as of yet there is no reliable clinical evidence that quercetin can prevent or treat cancer in humans." In the amounts consumed in a healthy diet, quercetin "is unlikely to cause any major problems or benefits."[4]

Adequate dietary intake of fruits and vegetables may reduce the risk of cancer.[5] Research shows that quercetin influences cellular mechanisms in vitro and, in animal studies, there is evidence from human population studies that quercetin may, in a very limited fashion, reduce the risk of certain cancers.[6][7]

Some researchers believe quercetin should not be used by healthy people (for prevention) until it can be shown that quercetin doesn't itself cause cancer. In laboratory studies of cells (in vitro), quercetin produces changes that are also produced by compounds that cause cancer (carcinogens), but these studies don't report increased cancer in animals or humans.[8][9][10] The U.S. Food and Drug Administration has not approved any health claims for quercetin.[11] There is current early-stage clinical research on quercetin addressing safety and efficacy against sarcoidosis, asthma and glucose absorption in obesity and diabetes (February 2009).[12]

Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin and quercitrin, found in citrus fruit, buckwheat and onions. Quercetin forms the glycosides quercitrin and rutin together with rhamnose and rutinose, respectively. Quercetin is classified as IARC group 3 (no evidence of carcinogenicity in humans).


Quercetin is a naturally-occurring polar auxin transport inhibitor.[citation needed]

Foods rich in quercetin include capers (1800 mg/kg)[13], lovage (1700 mg/kg), apples (44 mg/kg), tea (Camellia sinensis), onion, especially red onion (higher concentrations of quercetin occur in the outermost rings[14]), red grapes, citrus fruit, tomato, broccoli and other leafy green vegetables, and a number of berries including cherry, raspberry, bog whortleberry (158 mg/kg, fresh weight), lingonberry (cultivated 74 mg/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 53 mg/kg, wild 56 mg/kg),[15] and the fruit of the prickly pear cactus. A recent study found that organically grown tomatoes had 79% more quercetin than "conventionally grown".[16]

A study[17] 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.[18]


Biosynthesis of Quercetin.jpg The biosynthesis of quercetin is summarized in figure 4.[19] Phenylalanine(1) is converted to 4-coumaroyl-CoA(2) in a series of steps known as the general phenylpropanoid pathway using phenyl ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumaroylCoA-ligase. 4-coumaroyl-CoA(2) is added to three molecules of malonyl-CoA(3) to form tetrahydroxychalcone(4) using 7,2’-dihydroxy, 4’-methoxyisoflavanol synthase. Tetrahydroxychalcone(4) is then converted into naringenin(5) using chalcone isomerase. Naringenin(5) is then converted into eriodictyol(6) using flavanoid 3’ hydroxylase. Eriodictyol(6) is then converted into dihydroquercetin(7) with flavanone 3-hydroxylase which is then converted into quercetin using flavanol synthase.[20]

Possible medicinal properties

From in vitro studies, quercetin has demonstrated significant anti-inflammatory activity by inhibiting both manufacture and release of histamine and other allergic/inflammatory mediators.[citation needed] In addition, it exerts potent antioxidant activity and vitamin C-sparing action[citation needed].

In vitro, quercetin shows some antitumor activity.[citation needed] Cultured skin and prostate cancer cells showed significant mortality (compared to nonmalignant cells) when treated with a combination of quercetin and ultrasound.[21] 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.[citation needed]

Recent studies have supported that quercetin may help men with chronic prostatitis[22], and both men and women with interstitial cystitis, possibly because of its action as a mast cell inhibitor.[citation needed]

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[citation needed]. It also has been claimed to have antidepressant properties, however any claim of quercetin action against neurological diseases should be treated with skepticism due to the fact that quercetin is a neurotoxin in vitro.[23]

It has also been claimed that quercetin reduces blood pressure in hypertensive subjects.[24]

An 8-year study found that the presence of three flavonolskaempferol, quercetin, and myricetin — in the person's normal diet were associated with a reduced risk of pancreatic cancer, a rare but frequently fatal disease, of 23 percent in current tobacco smokers.[25] There was no benefit to people that have never smoked or that had previously quit smoking.

In mice, an oral quercetin dose of 12.5 to 25 mg/kg increased gene expression of mitochondrial biomarkers and improved exercise endurance.[26]

An in vitro study showed that quercetin and resveratrol combined inhibited production of fat cells.[27]

Despite these preliminary indications of possible health benefits, quercetin has neither been confirmed as a specific therapeutic for any condition nor has it been approved by any regulatory agency. A bioavailability study done on rats showed that ingested quercetin is extensively metabolized into non-active phenolic acids, with more than 96% of the ingested amount excreted within 72 hours, indicating actual physiological roles, if they exist, involve quercetin in only minute amounts.[28]

Drug interactions

Quercetin is contraindicated with some antibiotics; it may interact with fluoroquinolones (a type of medicinal antibiotic), as quercetin competitively binds to bacterial DNA gyrase. Whether this inhibits or enhances the effect of fluoroquinolones is not entirely clear.[29]

Quercetin is also a potent inhibitor of CYP3A4[30] and CYP2C9[31], which are enzymes that break down most drugs in the body. As such, quercetin would be expected to increase serum levels, and therefore effects, of drugs metabolized by this enzyme.

In cattle, there is a synergystic interaction between bovine papillomavirus-2 infection and exposure to quercetin, promoting bladder neoplasia, clinically presenting as enzootic haematuria. A similar effect is seen on exposure to the bracken fern Pteridium aqualinum, and the chemical ptaquiloside found within it.


See also


  1. ^ a b Laura K. Stewart, Jeff L. Soileau, David Ribnicky, Zhong Q. Wang, Ilya Raskin, Alexander Poulev, Martin Majewski, William T. Cefalu, and Thomas W. Gettys (2008). "Quercetin transiently increases energy expenditure but persistently decreases circulating markers of inflammation in C57BL/6J mice fed a high-fat diet". metabolism 57. 
  2. ^ a b c J. Mark Davis, E. Angela Murphy, Martin D. Carmichael, and Ben Davis (2009), "Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance", Am J Physiol Regul Integr Comp Physiol 296 
  3. ^ Phys Ed: Is Quercetin Really a Wonder Sports Supplement? By Gretchen Reynolds. New York Times, October 7, 2009. Review of the research.
  4. ^ American Cancer Society, Quercetin
  5. ^ "Guidance for Industry: A Food Labeling Guide XI. Appendix C: Health Claims, 21 CFR 101.76 and 21 CFR 101.78, April 2008". US Department of Health and Human Services, Food and Drug Administration. 
  6. ^ Neuhouser ML (2004). "Dietary flavonoids and cancer risk: evidence from human population studies". Nutr Cancer 50 (1): 1–7. doi:10.1207/s15327914nc5001_1. PMID 15572291. 
  7. ^ Murakami A, Ashida H, Terao J (October 2008). "Multitargeted cancer prevention by quercetin". Cancer Lett. 269 (2): 315–25. doi:10.1016/j.canlet.2008.03.046. PMID 18467024. 
  8. ^ Verschoyle RD, Steward WP, Gescher AJ (2007). "Putative cancer chemopreventive agents of dietary origin-how safe are they?". Nutr Cancer 59 (2): 152–62. doi:10.1080/01635580701458186 (inactive 2009-06-26). PMID 18001209. 
  9. ^ Rietjens IM, Boersma MG, van der Woude H, Jeurissen SM, Schutte ME, Alink GM (July 2005). "Flavonoids and alkenylbenzenes: mechanisms of mutagenic action and carcinogenic risk". Mutat. Res. 574 (1-2): 124–38. doi:10.1016/j.mrfmmm.2005.01.028. PMID 15914212. 
  10. ^ van der Woude H, Alink GM, van Rossum BE, et al. (December 2005). "Formation of transient covalent protein and DNA adducts by quercetin in cells with and without oxidative enzyme activity". Chem. Res. Toxicol. 18 (12): 1907–16. doi:10.1021/tx050201m. PMID 16359181. 
  11. ^ US FDA, Center for Food Safety and Nutrition, Qualified Health Claims Subject to Enforcement Discretion, April 2007[1]
  12. ^, National Institutes of Health
  13. ^ USDA Database for the Flavonoid Content of Selected Foods
  14. ^ Crystal Smith, Kevin A. Lombard, Ellen B. Peffley, Weixin Liu (2003). "Genetic Analysis of Quercetin in Onion (Allium cepa L.) Lady Raider" (). The Texas Journal of Agriculture and Natural Resource (Agriculture Consortium of Texas) 16: 24–8. 
  15. ^ Sari H. Häkkinen et al. (1999). "Content of the Flavonols Quercetin, Myricetin, and Kaempferol in 25 Edible Berries". Journal of Agricultural and Food Chemistry 47 (6): 2274–9. doi:10.1021/jf9811065. PMID 10794622. 
  16. ^ A. E. Mitchell, Y. J. Hong, E. Koh, D. M. Barrett, D. E. Bryant, R. F. Denison and S. Kaffka (2007). "Ten-Year Comparison of the Influence of Organic and Conventional Crop Management Practices on the Content of Flavonoids in Tomatoes". Journal of Agricultural and Food Chemistry 55 (15): 6154–9. doi:10.1021/jf070344. 
  17. ^ Honey Research Unit
  18. ^ honey fingerprinting
  19. ^ Biosynthesis of quercetin.
  20. ^ Winkel-Shirley, Brenda (June 2001). "Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology". Plant Physiol 126: 485-493. 
  21. ^ Paliwal S (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. 
  22. ^ 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. doi:10.1016/S0090-4295(99)00358-1. PMID 10604689. 
  23. ^ Ossola, B (2008). "Paradoxical co-existence of protective and toxic effects of quercetin in the same in vitro neurodegeneration model". European Journal of Pharmaceutical Sciences 34 (1): S33. doi:10.1016/j.ejps.2008.02.088. 
  24. ^ Edwards RL, Lyon T, Litwin SE, Rabovsky A, Symons JD, Jalili T (1 November 2007). "Quercetin reduces blood pressure in hypertensive subjects". J. Nutr. 137 (11): 2405–11. PMID 17951477. 
  25. ^ Ute Nöthlings, Suzanne P. Murphy, Lynne R. Wilkens, Brian E. Henderson3 and Laurence N. Kolonel (2007). "Flavonols and Pancreatic Cancer Risk". American Journal of Epidemiology 166 (8): 924–931. doi:10.1093/aje/kwm172. PMID 17690219. 
  26. ^ Davis JM, Murphy EA, Carmichael MD, Davis B. (2009). "Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance.". Am J Physiol Regul Integr Comp Physiol.. PMID 19211721. 
  27. ^ Yang JY, Della-Fera MA, Rayalam S, Ambati S, Hartzell DL, Park HJ, Baile CA (2008). "Enhanced inhibition of adipogenesis and induction of apoptosis in 3T3-L1 adipocytes with combinations of resveratrol and quercetin". Life Sci. 82 (19-20): 1032–9. doi:10.1016/j.lfs.2008.03.003. PMID 18433793. 
  28. ^ Mullen W et al. (December 2008). "Bioavailability of [2-(14)C]quercetin-4'-glucoside in rats.". J Agric Food Chem. 2456 (24): 12127–37. doi:10.1021/jf802754s. PMID 19053221. 
  29. ^ Hilliard JJ, Krause HM, Bernstein JI, et al. (1995). "A comparison of active site binding of 4-quinolones and novel flavone gyrase inhibitors to DNA gyrase". Adv. Exp. Med. Biol. 390: 59–69. PMID 8718602. 
  30. ^ Su-Lan Hsiu; Yu-Chi Hou; Yao-Horng Wang; Chih-Wan Tsao; Sheng-Fang Sue; and Pei-Dawn L. Chao (6 December 2002). "Quercetin significantly decreased cyclosporin oral bioavailability in pigs and rats". Life Sciences 72 (3): 227–235. doi:10.1016/S0024-3205(02)02235-X. 
  31. ^ Si Dayong, Wang Y, Zhou Y-H, Guo Y, Wang J, Zhou H, Li Z-S, Fawcett JP (March 2009). "Mechanism of CYP2C9 inhibition by flavones and flavonols". Drug Metabolism and Disposition 37: 629–634.. doi:10.1124/dmd.108.023416. PMID 19074529. 

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