quercetin
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Occurrence
- widely distributed in plants, especially rinds & barks, clover blossoms & ragweed pollen
- in red onions, higher concentrations of quercetin occur in the outermost rings & in the part closest to the root[2]
- quercetin glycosides are normal dietary constituents
- quercetin itself is not
- quercetin is found in tomatoes, kale, apples, & tea[5]
Indications
no confirmation of specific therapeutic for any condition
- not approved by any regulatory agency
- European Food Safety Authority evaluated possible health claims associated with consumption of quercetin, finding that no cause-&-effect relationship has been established for any physiological effect[3]
uses[4]
- allergies, asthma, hay fever and hives
- no evidence yet that it works in humans
- cardiovascular risk reduction
- more studies in people are needed
- hypertension
- quercetin supplementation may reduce blood pressure
- interstitial cystitis
- more & better designed studies are needed
- prostatitis
- one small study found benefit; results need to be confirmed
- rheumatoid arthritis -no evidence that quercetin supplements beneficial
- cancer prevention
- frequent intake of quercetin glycoside rich foods associated with lower lung cancer risk[4]
Dosage
- available as pills or capsules
- often packaged with bromelain
- present in flavonoid rich extracts including those from grape seed, bilberry, Ginkgo biloba, & green tea
- water soluble forms of quercetin available
- hesperidn-methyl-chalcone
- quercetin-chalcone
- < 1 gram/day would be prudent
Adverse effects
- quercitin is allegedly highly toxic[1]
- generally considered safe[4]
- headache
- dyspepsia
- high doses of quercetin (> 1 gram/day) may be nephrotoxic
Drug interactions
- may interact with fluoroquinolones
- inhibits CYP2C8, thus may unpredictably increase paclitaxel levels
- may interact with warfarin, clopidogrel, aspirin[4]
- may enhance the effects of doxorubicin & cisplatin[4]
- may prolong 1/2 life of glucocorticoids
- may inhibit absorption of cyclosporine
- may increase risk of digoxin toxicity[4]
Mechanism of action
- antioxidant
- protein tyrosine kinase (PTK) inhibitor
- inhibits cAMP-dependent kinase, protein kinase C, casein kinase 2 & other ATP requiring enzymes
- competitively binds to bacterial DNA gyrase
More general terms
Component of
- bioflavonoid/quercetin
- bilberry/bioflavonoid/quercetin/rutin
- ascorbate/quercetin
- ascorbate/pantothenate/quercetin
References
- ↑ 1.0 1.1 Merck Index, I2th ed, Merck & Co, Rahway NJ, 1996 # 8216
- ↑ 2.0 2.1 Wikipedia: Quercitin http://en.wikipedia.org/wiki/Quercetin
- ↑ 3.0 3.1 EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) 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. EFSA Journal 2011;9(4):2067[15 pp.] http://www.efsa.europa.eu/en/efsajournal/pub/2067.htm
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 University of Maryland Medical Center http://umm.edu/health/medical/altmed/supplement/quercetin
- ↑ 5.0 5.1 George J Flavonols Linked to Slower Cognitive Decline. Memory scores better in older adults who ate more flavonol-rich fruits and vegetables. MedPage Today November 23, 2022 https://www.medpagetoday.com/neurology/dementia/101921
Holland TM, Agarwal P, Wang Y et al Association of Dietary Intake of Flavonols With Changes in Global Cognition and Several Cognitive Abilities. Neurology. November 22, 2022 PMID: https://www.ncbi.nlm.nih.gov/pubmed/36414424 https://n.neurology.org/content/early/2022/11/22/WNL.0000000000201541