Quercetin

{{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 415155335 | Name = Quercetin | pronounce = {{IPAc-en|ˈ|k|w|ɜːr|s|ᵻ|t|ᵻ|n}} | ImageFile = Quercetin.svg | ImageClass = skin-invert-image | ImageSize = 250px | ImageAlt = Skeletal formula of quercetin | ImageFile1 = Quercetin-3D-balls.png | ImageClass1 = bg-transparent | ImageAlt1 = Ball-and-stick model of the quercetin molecule | IUPACName = 3,3′,4′,5,7-Pentahydroxyflavone | SystematicName = 2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-4''H''-1-benzopyran-4-one | OtherNames = 5,7,3′,4′-flavon-3-ol, Sophoretin, Meletin, Quercetine, Xanthaurine, Quercetol, Quercitin, Quertine, Flavin meletin |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 117-39-5 | CASNo2_Ref = {{cascite|correct|CAS}} | CASNo2 = 6151-25-3 | CASNo2_Comment = (dihydrate)<ref name=PVP>{{Cite web|url=http://www.pvp.com.br/EN_quercetin_dihydrate_safety_data.htm|archive-url=https://web.archive.org/web/20110916172444/http://www.pvp.com.br/EN_quercetin_dihydrate_safety_data.htm|url-status= dead|title=Quercetin dihydrate safety sheet|archive-date=September 16, 2011}}</ref> | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 16243 | Beilstein = 317313 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 50 | ChemSpiderID = 4444051 | DrugBank_Ref = {{drugbankcite|correct|drugbank}} | DrugBank = DB04216 | EINECS = 204-187-1 | Gmelin = 579210 | IUPHAR_ligand = 5346 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C00389 | PubChem = 5280343 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 9IKM0I5T1E | UNII1_Ref = {{fdacite|correct|FDA}} | UNII1 = 53B03V78A6 | UNII1_Comment = (dihydrate) | UNNumber = 2811 | InChI = 1/C15H10O7/c16-7-4-10(19)12-11(5-7)22-15(14(21)13(12)20)6-1-2-8(17)9(18)3-6/h1-5,16-19,21H | InChIKey = REFJWTPEDVJJIY-UHFFFAOYAW | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C15H10O7/c16-7-4-10(19)12-11(5-7)22-15(14(21)13(12)20)6-1-2-8(17)9(18)3-6/h1-5,16-19,21H | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = REFJWTPEDVJJIY-UHFFFAOYSA-N | SMILES = O=C1c3c(O/C(=C1/O)c2ccc(O)c(O)c2)cc(O)cc3O }} |Section2={{Chembox Properties | Formula = C15H10O7 | MolarMass = 302.236 g/mol | Density = 1.799 g/cm3 | MeltingPtC = 316 | BoilingPt = | Appearance = yellow crystalline powder<ref name=PVP/> | Solubility = Practically insoluble in water; soluble in aqueous alkaline solutions<ref name=PVP/> }} }} thumb|right|class=skin-invert-image|UV visible spectrum of quercetin, with lambda max at 369 nm

'''Quercetin''' is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it.<ref name="lpi">{{cite web|url=http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids|title=Flavonoids |publisher=Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, OR|date=November 2015|access-date=1 April 2018}}</ref><ref name=usda/> It has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.

== Occurrence == Quercetin is a flavonoid widely distributed in nature.<ref name=lpi/> The name has been used since 1857, and is derived from ''quercetum'' (oak forest), after the oak genus ''Quercus''.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/quercetin|title=Quercetin|date=29 November 2023 |publisher=Merriam-Webster}}</ref><ref>{{cite web|url=http://www.britannica.com/EBchecked/topic/487030/quercitin|title=Quercetin (biochemistry)|publisher=Encyclopædia Britannica}}</ref> It is a naturally occurring polar auxin transport inhibitor.<ref name="pmid12237347">{{cite journal | vauthors = Fischer C, Speth V, Fleig-Eberenz S, Neuhaus G | title = Induction of Zygotic Polyembryos in Wheat: Influence of Auxin Polar Transport | journal = The Plant Cell | volume = 9 | issue = 10 | pages = 1767–1780 | date = Oct 1997 | pmid = 12237347 | pmc = 157020 | doi = 10.1105/tpc.9.10.1767 }}</ref>

Quercetin is one of the most abundant dietary flavonoids,<ref name=lpi/><ref name=usda>{{cite web |url=https://www.ars.usda.gov/ARSUserFiles/80400525/Data/Flav/Flav_R03.pdf |title=USDA Database for the Flavonoid Content of Selected Foods, Release 3 |year=2011 |publisher=U.S. Department of Agriculture}}</ref> with an average daily consumption of 25–50 mg.<ref name="pmid8847003">{{cite journal | vauthors = Formica JV, Regelson W | title = Review of the biology of quercetin and related bioflavonoids | journal = Food and Chemical Toxicology | volume = 33 | issue = 12 | pages = 1061–80 | year = 1995 | pmid = 8847003 | doi = 10.1016/0278-6915(95)00077-1 }}</ref>

{| class="wikitable sortable" |- ! Foods !! data-sort-type="number" | Quercetin, mg / 100 g |- | capers, raw || 234<ref name=usda/> |- | capers, canned || 173<ref name=usda/> |- | lovage leaves, raw || 170<ref name=usda/> |- | dock like sorrel || 86<ref name=usda/> |- | radish leaves || 70<ref name=usda/> |- | carob fiber || 58<ref name=usda/> |- | dill weed, fresh || 55<ref name=usda/> |- | coriander || 53<ref name=usda/> |- | yellow wax pepper, raw || 51<ref name=usda/> |- | fennel leaves || 49<ref name=usda/> |- | onion, red || 32<ref name=usda/> |- | radicchio || 32<ref name=usda/> |- | watercress || 30<ref name=usda/> |- | kale || 23<ref name=usda/> |- | chokeberry || 19<ref name=usda/> |- | bog blueberry || 18<ref name=usda/> |- | buckwheat seeds || 15<ref name=usda/> |- | cranberry || 15<ref name=usda/> |- | lingonberry || 13<ref name=usda/> |- | plums, black || 12<ref name=usda/> |- |} In red onions, higher concentrations of quercetin occur in the outermost rings and in the part closest to the root, the latter being the part of the plant with the highest concentration.<ref>{{cite journal | vauthors = Slimestad R, Fossen T, Vågen IM | title = Onions: a source of unique dietary flavonoids | journal = Journal of Agricultural and Food Chemistry | volume = 55 | issue = 25 | pages = 10067–80 | date = December 2007 | pmid = 17997520 | doi = 10.1021/jf0712503 | bibcode = 2007JAFC...5510067S }}</ref> One study found that organically grown tomatoes had 79% more quercetin than non-organically grown fruit.<ref name="pmid17590007">{{cite journal | vauthors = Mitchell AE, Hong YJ, Koh E, Barrett DM, Bryant DE, Denison RF, Kaffka S | title = Ten-year comparison of the influence of organic and conventional crop management practices on the content of flavonoids in tomatoes | journal = Journal of Agricultural and Food Chemistry | volume = 55 | issue = 15 | pages = 6154–9 | date = Jul 2007 | pmid = 17590007 | doi = 10.1021/jf070344+ | bibcode = 2007JAFC...55.6154M }}</ref> Quercetin is present in various kinds of honey from different plant sources.<ref name="pmid21229237">{{cite journal | vauthors = Petrus K, Schwartz H, Sontag G | title = Analysis of flavonoids in honey by HPLC coupled with coulometric electrode array detection and electrospray ionization mass spectrometry | journal = Analytical and Bioanalytical Chemistry | volume = 400 | issue = 8 | pages = 2555–63 | date = Jun 2011 | pmid = 21229237 | doi = 10.1007/s00216-010-4614-7 | s2cid = 24796542 }}</ref>

== Biosynthesis ==

In plants, phenylalanine is converted to 4-coumaroyl-CoA in a series of steps known as the general phenylpropanoid pathway using phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumaroyl-CoA-ligase.<ref name="pmid11402179">{{cite journal | vauthors = Winkel-Shirley B | title = Flavonoid biosynthesis. A colorful model for genetics, biochemistry, cell biology, and biotechnology | journal = Plant Physiology | volume = 126 | issue = 2 | pages = 485–93 | date = Jun 2001 | pmid = 11402179 | pmc = 1540115 | doi = 10.1104/pp.126.2.485 }}</ref> One molecule of 4-coumaroyl-CoA is added to three molecules of malonyl-CoA to form tetrahydroxychalcone using 7,2′-dihydroxy-4′-methoxyisoflavanol synthase. Tetrahydroxychalcone is then converted into naringenin using chalcone isomerase.

Naringenin is converted into eriodictyol using flavanoid 3′-hydroxylase. Eriodictyol is then converted into dihydroquercetin with flavanone 3-hydroxylase, which is then converted into quercetin using flavonol synthase.<ref name="pmid11402179"/>

=== Glycosides === thumb|class=skin-invert-image|3-O-Glycosides of quercetin

Quercetin is the aglycone form of a number of other flavonoid glycosides, such as rutin (also known as quercetin-3-O-rutinoside) and quercitrin, found in citrus fruit, buckwheat, and onions.<ref name=lpi/> Quercetin forms the glycosides quercitrin and rutin together with rhamnose and rutinose, respectively. Likewise guaijaverin is the 3-''O''-arabinoside, hyperoside is the 3-''O''-galactoside, isoquercitin is the 3-''O''-glucoside and spiraeoside is the 4′-''O''-glucoside. CTN-986 is a quercetin derivative found in cottonseeds and cottonseed oil. Miquelianin is the quercetin 3-''O''-β-D-glucuronopyranoside.<ref name="pmid14735439">{{cite journal | vauthors = Juergenliemk G, Boje K, Huewel S, Lohmann C, Galla HJ, Nahrstedt A | title = In vitro studies indicate that miquelianin (quercetin 3-''O''-beta-D-glucuronopyranoside) is able to reach the CNS from the small intestine | journal = Planta Medica | volume = 69 | issue = 11 | pages = 1013–7 | date = Nov 2003 | pmid = 14735439 | doi = 10.1055/s-2003-45148 | s2cid = 260253046 }}</ref>

Several taxifolin (also known as dihydroquercetin) glycosides also exist. Isoquercetin is the 3-''O''-glucoside of quercetin.

=== Rutin degradation pathway ===

The enzyme quercitrinase can be found in ''Aspergillus flavus''.<ref name="urlInformation on EC 3.2.1.66 - quercitrinase">{{cite web | url = http://www.brenda-enzymes.org/php/result_flat.php4?ecno=3.2.1.66 | title = Information on EC 3.2.1.66 - quercitrinase | publisher = Helmholtz Centre for Infection Research | work = BRENDA (BRaunschweig ENzyme DAtabase) }}</ref> This enzyme hydrolyzes the glycoside quercitrin to release quercetin and L-rhamnose. It is an enzyme in the rutin catabolic pathway.<ref name="pmid20419500">{{cite journal | vauthors = Tranchimand S, Brouant P, Iacazio G | title = The rutin catabolic pathway with special emphasis on quercetinase | journal = Biodegradation | volume = 21 | issue = 6 | pages = 833–59 | date = Nov 2010 | pmid = 20419500 | doi = 10.1007/s10532-010-9359-7 | s2cid = 30101803 }}</ref>

== Pharmacology ==

=== Pharmacokinetics === The bioavailability of quercetin in humans after oral intake is very low, with one study concluding it must be less than 1%.<ref name="pharmokinetics">{{cite journal |last1=Gugler |first1=R. |last2=Leschik |first2=M. |last3=Dengler |first3=H. J. |title=Disposition of quercetin in man after single oral and intravenous doses |journal=European Journal of Clinical Pharmacology |date=1 March 1975 |volume=9 |issue=2 |pages=229–234 |doi=10.1007/BF00614022|pmid=1233267 |s2cid=23812714 }}</ref> Intravenous injection of quercetin shows a rapid decay in concentration described by a two-compartment model (initial half-life of 8.8 minutes, terminal half-life of 2.4 hours).<ref name="pharmokinetics"/> Because it undergoes rapid and extensive metabolism, the biological effects presumed from ''in vitro'' studies are unlikely to apply ''in vivo''.<ref name=lpi/><ref name=Williams>{{cite journal | vauthors = Williams RJ, Spencer JP, Rice-Evans C | title = Flavonoids: antioxidants or signalling molecules? | journal = Free Radical Biology & Medicine | volume = 36 | issue = 7 | pages = 838–49 | date = Apr 2004 | pmid = 15019969 | doi = 10.1016/j.freeradbiomed.2004.01.001 | department = (review) }}</ref><ref>{{cite journal | vauthors = Barnes S, Prasain J, D'Alessandro T, Arabshahi A, Botting N, Lila MA, Jackson G, Janle EM, Weaver CM | title = The metabolism and analysis of isoflavones and other dietary polyphenols in foods and biological systems | journal = Food & Function | volume = 2 | issue = 5 | pages = 235–44 | date = May 2011 | pmid = 21779561 | doi = 10.1039/c1fo10025d | department = (review) | pmc=4122511}}</ref><ref name="pmid30614249">{{cite journal | vauthors=Luca SV, Macovei I, Bujor A, Trifan A | title=Bioactivity of dietary polyphenols: The role of metabolites | journal=Critical Reviews in Food Science and Nutrition | volume=60 | issue=4 | pages=626–659 | year=2020 | doi = 10.1080/10408398.2018.1546669 | pmid=30614249| bibcode=2020CRFSN..60..626L | s2cid=58651581 }}</ref> Quercetin supplements in the aglycone form are less bioavailable than the quercetin glycoside often found in foods, especially red onions.<ref name=lpi/><ref name="pmid31557798">{{cite journal | vauthors = Dabeek WM, Marra MV | title = Dietary Quercetin and Kaempferol: Bioavailability and Potential Cardiovascular-Related Bioactivity in Humans | journal = Nutrients | volume = 11 | issue=10 | pages = 2288 | date=2019 | doi = 10.3390/nu11102288 | pmc=6835347 | pmid = 31557798| doi-access = free }}</ref> Ingestion with high-fat foods may increase bioavailability compared to ingestion with low-fat foods,<ref name="pmid31557798" /> and carbohydrate-rich foods may increase absorption of quercetin by stimulating gastrointestinal motility and colonic fermentation.<ref name=lpi/> Whereas quercetin has been shown to be a potent anti-inflammatory compound in a variety of in vitro and in vivo bioassay models, oral quercetin in human subjects has not exhibited the desired effects.<ref name="pmid34248976">{{cite journal |vauthors=Shen P, Lin W, Deng X, Ba X, Han L, Chen Z, Qin K, Huang Y, Tu S |title=Potential Implications of Quercetin in Autoimmune Diseases |journal=Front Immunol |volume=12 |issue= |article-number=689044 |date=2021 |pmid=34248976 |pmc=8260830 |doi=10.3389/fimmu.2021.689044 |doi-access=free |url=}}</ref> Because of low solubility and poor bioavailability of quercetin, derivatives have been synthesized to overcome these challenges and enhance its biological activity, leading to compounds with improved properties for possible therapeutic applications.<ref name="pmid34971873">{{cite journal |vauthors=Alizadeh SR, Ebrahimzadeh MA |title=Quercetin derivatives: Drug design, development, and biological activities, a review |journal=Eur J Med Chem |volume=229 |issue= |article-number=114068 |date=February 2022 |pmid=34971873 |doi=10.1016/j.ejmech.2021.114068 |s2cid=245485982 |url=}}</ref>

=== Metabolism === Quercetin is rapidly metabolized (via glucuronidation) after the ingestion of quercetin foods or supplements.<ref name="pmid10363620">{{cite journal | vauthors = Graefe EU, Derendorf H, Veit M | title = Pharmacokinetics and bioavailability of the flavonol quercetin in humans | journal = International Journal of Clinical Pharmacology and Therapeutics | volume = 37 | issue = 5 | pages = 219–33 | year = 1999 | pmid = 10363620 | url = http://ucce.ucdavis.edu/files/datastore/608-67.pdf | department = (review) | access-date = 2016-01-01 | archive-date = 2017-05-17 | archive-url = https://web.archive.org/web/20170517030352/http://ucce.ucdavis.edu/files/datastore/608-67.pdf | url-status = dead }}</ref> Five metabolites (quercetin glucuronides) have been found in human plasma after quercetin ingestion.<ref>{{cite journal |last1=Wittig |first1=Jörg |last2=Herderich |first2=Markus |last3=Graefe |first3=Eva Ulrike |last4=Veit |first4=Markus |title=Identification of quercetin glucuronides in human plasma by high-performance liquid chromatography–tandem mass spectrometry |journal=Journal of Chromatography B: Biomedical Sciences and Applications |date=April 2001 |volume=753 |issue=2 |pages=237–243 |doi=10.1016/s0378-4347(00)00549-1|pmid=11334336 }}</ref><ref name="pmid10363620"/> Taken together, the quercetin glucuronides have a half-life around 11–12 hours.<ref name="pmid10363620"/>

In rats, quercetin did not undergo any significant phase I metabolism.<ref name = "Day_2004"/> In contrast, quercetin did undergo extensive phase II (conjugation) to produce metabolites that are more polar than the parent substance, hence are more rapidly excreted from the body. ''In vitro'', the meta-hydroxyl group of catechol is methylated by catechol-O-methyltransferase. Four of the five hydroxyl groups of quercetin are glucuronidated by UDP-glucuronosyltransferase. The exception is the 5-hydroxyl group of the flavonoid ring, which generally does not undergo glucuronidation. The major metabolites of orally absorbed quercetin are quercetin-3-glucuronide, 3'-methylquercetin-3-glucuronide, and quercetin-3'-sulfate.<ref name = "Day_2004">{{cite book | veditors = Bao Y, Fenwick R | title = Phytochemicals in health and disease | chapter = Characterization of polyphenol metabolites | vauthors = Day AJ, Rothwell JA, Morgan RA | date = 2004 | publisher = Dekker | location = New York, NY | isbn = 0-8247-4023-8 | pages = 50–67 | chapter-url = https://books.google.com/books?id=ruD5AWlELmgC&q=Quercetin%20%E2%80%8E%20estrogen%20receptor&pg=PA58}}</ref> A methyl metabolite of quercetin has been shown ''in vitro ''to be more effective than quercetin at inhibiting lipopolysaccharide-activated macrophages.<ref name="pmid30614249" />

Compared to other flavonoids, quercetin is one of the most effective inducers of the phase II detoxification enzymes.<ref name="pmid21277359">{{cite journal | vauthors=Procházková D, Boušová I, Wilhelmová N | title=Antioxidant and prooxidant properties of flavonoids | journal=Fitoterapia | volume=82 | issue=4 | pages=513–523 | year=2011 | doi = 10.1016/j.fitote.2011.01.018 | pmid=21277359| doi-access=free | hdl=11104/0202202 | hdl-access=free }}</ref>

''In vitro'' studies show that quercetin is a strong inhibitor of the cytochrome P450 enzymes CYP3A4 and CYP2C19 and a moderate inhibitor of CYP2D6.<ref>{{cite journal | vauthors = Elbarbry F, Ung A, Abdelkawy K | title = Studying the Inhibitory Effect of Quercetin and Thymoquinone on Human Cytochrome P450 Enzyme Activities | journal = Pharmacognosy Magazine | volume = 13 | issue = Suppl 4 | pages = S895–S899 | date = January 2018 | pmid = 29491651 | pmc = 5822518 |doi = 10.4103/0973-1296.224342 |doi-broken-date = 11 May 2026 |doi-access=free}}</ref><ref>{{cite journal |last1=Rastogi |first1=Himanshu |last2=Jana |first2=Snehasis |title= Evaluation of Inhibitory Effects of Caffeic acid and Quercetin on Human Liver Cytochrome P450 Activities|journal=Phytotherapy Research |date=December 2014 |volume=28 |issue=12 |pages=1873–1878 |doi=10.1002/ptr.5220|pmid=25196644 |s2cid=41563915 |doi-access=free }}</ref> Drugs that are metabolized by these pathways may have increased effect. An ''in vivo'' study found that quercetin supplementation slows the metabolism of caffeine to a statistically significant extent in a particular genetic subpopulation, but in absolute terms the effect was almost negligible.<ref>{{cite journal |title= Quercetin Significantly Inhibits the Metabolism of Caffeine, a Substrate of Cytochrome P450 1A2 Unrelated to ''CYP''1''A''2*1''C'' (−2964G>A) and 1''F''* (734C>A) Gene Polymorphisms|journal= BioMed Research International|year= 2014|doi=10.1155/2014/405071|doi-access= free|last1= Xiao|first1= Jian|last2= Huang|first2= Wei-Hua|last3= Peng|first3= Jing-Bo|last4= Tan|first4= Zhi-Rong|last5= Ou-Yang|first5= Dong-Sheng|last6= Hu|first6= Dong-Li|last7= Zhang|first7= Wei|last8= Chen|first8= Yao|volume= 2014|pages= 1–6|pmid= 25025048|pmc= 4082882}}</ref> Quercetin is an inhibitor of CYP1B1<ref>{{cite journal | last1=Ma|first1=Dujun|last2=Yu |first2=Tian|last3=Peng |first3= Liping| last4=Wang|first4= Lixin|last5=Liao |first5= Zhouwei|last6=Xu|first6= Wenming| date = 15 July 2019 | title = PIM1, CYP1B1, and HSPA2 Targeted by Quercetin Play Important Roles in Osteoarthritis Treatment by Achyranthes bidentata | journal = Evidence-Based Complementary and Alternative Medicine | article-number=1205942 | pmid = 31998395 |pmc=6964619 | doi = 10.1155/2019/1205942 |doi-access=free }}</ref> and CYP46A1.<ref>{{cite journal |title=Identification of potential inhibitors of brain-specific CYP46A1 from phytoconstituents in Indian traditional medicinal plants |journal=J Proteins Proteom |date=16 November 2022 |volume=13 |issue=4 |pages=227–245 |doi=10.1007/s42485-022-00098-x |pmc=9667835|pmid=36404953|author=Kaur K, Devi B, Agrawal V, Kumar R, Sandhir R}}</ref>

==Food safety== In 2010, the U. S. Food and Drug Administration  acknowledged high-purity quercetin as generally recognized as safe  for use as an ingredient in various specified food categories at levels up to 500 mg per serving.<ref name=GRN341>{{cite web|title=GRN No. 341 (Quercetin)|url=https://www.accessdata.fda.gov/scripts/fdcc/index.cfm?set=GRASNotices&id=341|archive-url=https://web.archive.org/web/20160222091423/http://www.accessdata.fda.gov/scripts/fdcc/index.cfm?set=GRASNotices&id=341|url-status=dead|archive-date=February 22, 2016|publisher=US Food and Drug Administration|date=22 November 2010|access-date=27 October 2021}}</ref>

== Health claims == Quercetin has been studied in basic research and small clinical trials.<ref name=lpi/><ref>{{cite journal |vauthors=Yang F, Song L, Wang H, Wang J, Xu Z, Xing N |title=Quercetin in prostate cancer: Chemotherapeutic and chemopreventive effects, mechanisms and clinical application potential (Review) |journal=Oncol. Rep. |volume=33 |issue=6 |pages=2659–68 |date=June 2015 |pmid=25845380 |doi=10.3892/or.2015.3886 |doi-access=free }}</ref><ref name="roles">{{citation | title = New Roles for Polyphenols. A 3-Part Report on Current Regulations & the State of Science | vauthors = Gross P | date = March 1, 2009 | publisher = Nutraceuticals World | url = http://www.nutraceuticalsworld.com/issues/2009-03/view_features/new-roles-for-polyphenols/ | access-date = September 24, 2014 | archive-date = October 19, 2021 | archive-url = https://web.archive.org/web/20211019014809/https://www.nutraceuticalsworld.com/issues/2009-03/view_features/new-roles-for-polyphenols/ | url-status = dead }}</ref><ref name="pmid25323953">{{cite journal | vauthors = Miles SL, McFarland M, Niles RM | title = Molecular and physiological actions of quercetin: need for clinical trials to assess its benefits in human disease | journal = Nutrition Reviews | volume = 72 | issue = 11 | pages = 720–34 | year = 2014 | pmid = 25323953 | doi = 10.1111/nure.12152 | doi-access = free }}</ref> While supplements have been promoted for the treatment of cancer and various other diseases,<ref name=lpi/> there is no high-quality evidence that quercetin (via supplements or in food) is useful to treat cancer<ref name=acs>{{cite book |publisher=American Cancer Society |title=American Cancer Society Complete Guide to Complementary and Alternative Cancer Therapies |edition=2nd |year=2009 |isbn=9780944235713 |veditors=Ades TB |chapter=Quercetin |url-access=registration |url=https://archive.org/details/americancancerso0000unse }}</ref> or any other disease.<ref name=lpi/><ref name="efsa">{{cite journal | author = European Food Safety Agency (EFSA) NDA Panel (Dietetic Products, Nutrition and Allergies) | title = Scientific Opinion on the substantiation of health claims related to quercetin and protection of DNA, proteins and lipids from oxidative damage (ID 1647), "cardiovascular system" (ID 1844), "mental state and performance" (ID 1845), and "liver, kidneys" (ID 1846) pursuant to Article 13(1) of Regulation (EC) No 1924/2006 | journal = EFSA Journal | date = 8 April 2011 | volume = 9 | issue = 4 | pages = 2067–82 | doi = 10.2903/j.efsa.2011.2067 | doi-access = free | pmid = 42078714 | pmc = 13129588 }}</ref>

The US Food and Drug Administration has issued warning letters to several manufacturers advertising on their product labels and websites that quercetin product(s) can be used to treat diseases.<ref name="fda">{{cite web | url = https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2017/ucm545773.htm | archive-url = https://web.archive.org/web/20170404201025/https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2017/ucm545773.htm | url-status = dead | archive-date = April 4, 2017 | title = Warning Letter to Cape Fear Naturals | date = 2 March 2017 | vauthors = King JL | publisher = Inspections, Compliance, Enforcement, and Criminal Investigations, US Food and Drug Administration | access-date = 29 November 2018 }}</ref><ref name="fda2">{{cite web|url=https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2017/ucm554022.htm|archive-url=https://web.archive.org/web/20170430202320/https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/2017/ucm554022.htm|url-status=dead|archive-date=April 30, 2017|title=Warning Letter to DoctorVicks.com|publisher=Inspections, Compliance, Enforcement, and Criminal Investigations, US Food and Drug Administration|date=17 April 2017| vauthors = Pace R |access-date=29 November 2018}}</ref> The FDA regards such quercetin advertising and products as unapproved – with unauthorized health claims concerning the anti-disease products – as defined by "sections 201(g)(1)(B) and/or 201 (g)(1)(C) of the Act [21 U.S.C. § 321(g)(1)(B) and/or 21 U.S.C. § 321(g)(1)(C)] because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease",<ref name=fda/><ref name=fda2/> conditions not met by the manufacturers.

===Safety=== Little research has been conducted into the safety of quercetin supplementation in humans, and the results are insufficient to give confidence that the practice is safe. In particular, a lack of safety information exists on the effect of quercetin supplementation for pregnant women, breastfeeding women, children, and adolescents. The hormonal effects of quercetin found in animal studies raise the suspicion of a parallel effect in humans, particularly in respect of estrogen-dependent tumors.<ref name=andres/>

Quercetin supplementation can interfere with the effects of medications. The precise nature of this interaction is known for some common medicines, but for many, it is not.<ref name=andres>{{cite journal |vauthors=Andres S, Pevny S, Ziegenhagen R, Bakhiya N, Schäfer B, Hirsch-Ernst KI, Lampen A |title=Safety Aspects of the Use of Quercetin as a Dietary Supplement |journal=Mol Nutr Food Res |volume=62 |issue=1 |date=January 2018 |article-number=1700447 |pmid=29127724 |doi=10.1002/mnfr.201700447 |s2cid=24772872 |type=Review|doi-access=free }}</ref>

== References == {{Reflist}}

==External links== *{{Commons category-inline}}

{{Flavonols}} {{Antioxidants}} {{Phytoestrogens}} {{Estrogen receptor modulators}} {{Purine receptor modulators}} {{Authority control}}

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