Quercetin is a flavonoid, a substance found in fruits, flowers, and
vegetables that, among other functions, gives them their color. The average
daily intake of flavonoids in the United States is between 150 and 200 mg. In
general, flavonoids have been found to have both antioxidant and
anti-inflammatory properties, useful in preventing or treating many health
conditions. The thousands of flavonoid compounds can be placed into a handful of
categories—one of which is quercetin. Quercetin can
decrease allergic reactions and may be beneficial in treating other inflammatory
responses, such as canker sores, hives, asthma, and arthritis. Other conditions
for which quercetin may be beneficial include diabetes mellitus, dysentery,
gout, heart disease, infections, inflammatory bowel disease, cataracts, atopic
dermatitis, and psoriasis.
Recently, research has focused on prevention of carcinogenesis. Quercetin may
be helpful in the prevention of skin carcinogenesis and has demonstrated
antitumor activity in patients with ovarian cancer and hepatoma. Further
clinical studies are needed to confirm these results.
Fruits and vegetables, particularly citrus fruits, apples, onions, parsley,
tea, and red wine.
Quercetin is a flavonoid. Flavonoids are found in fruits and vegetables, are
ascorbic-acid-related substances, and are compounds that are in human diets as
glycosides. Research suggests, however, that many of the biologic effects are
associated with aglycone, a substance that is released in the intestine, rather
than with the compound bound in the glycoside.
- Quercetin is available commercially in several strengths in powder or
- Quercetin is often packaged with bromelain as an anti-inflammatory
- Flavonoid-rich extracts include those from grape seed, bilberry,
Ginkgo biloba, and green tea. Quercetin is one of the many flavonoids
these substances contain.
- Allergies and hives: Research shows that quercetin inhibits histamine
release from basophils and mast cells.
- Asthma: Quercetin has been shown to inhibit histamine release, as with
- Canker sores: Quercetin may be beneficial in the treatment of canker
sores by increasing the number of ulcer-free days and by producing mild
- Diabetes mellitus: Quercetin can reduce the accumulation of sorbitol
in lens tissues, and thus may be beneficial in preventing cataracts,
retinopathy, neuropathy, and other complications of diabetes mellitus.
Flavonoids, including quercetin, promote insulin secretion, increase
intracellular vitamin C levels, protect blood vessels, prevent easy bruising,
and support the immune system, all of which are beneficial to individuals with
- Dysentery: Quercetin and tocopherol in combination were found to
restore the immune homeostasis and to normalize clinical indices in patients
- Gout: Quercetin inhibits uric acid production, as well as the
manufacture and release of inflammatory compounds.
- Heart disease: Although studies are not conclusive on the benefits of
quercetin in the treatment of coronary disease, it has been shown that
individuals with very low intakes of flavonoids are at higher risk.
- Infection: Quercetin inhibits infectiousness and/or replication of
such viruses as herpes simplex type 1, polio virus type 1, parainfluenza virus
type 3, and respiratory syncytial virus.
- Psoriasis: Quercetin inhibits lipoxygenase.
- Rheumatoid arthritis: Quercetin may be beneficial by inhibiting mast
cell degranulation, thus reducing tissue destruction.
|Dosage Ranges and Duration of
- 100 to 250 mg tid is thought to be an effective general
- 250 to 600 mg per day, divided in several doses, is effective in
reducing histamine levels and allergy symptoms.
- 200 to 400 mg of quercetin should be taken with bromelain between
meals tid for the treatment of gout. (Bromelain both enhances the absorption of
quercetin and provides anti-inflammatory effects of its own.)
- 200 to 400 mg of quercetin should be taken approximately 20 minutes
before each meal for the treatment of chronic hives. Acute symptoms of allergies
or outbreaks of hives can be treated with 800 mg qid.
No side effects have been associated with quercetin.
No problems with quercetin have been demonstrated.
In vitro, quercetin (1 and 10 mM) potentiated the effects of adriamycin on
MCF-7 ADR resistant human breast cancer cells by inhibiting growth in a
dose-dependent manner (Scambia et al. 1994). Concomitant treatment with
quercetin (20 mg/kg) and cisplatin (3 mg/kg) in mice implanted with human
large-cell lung cancer reduced tumor growth to a greater degree than cisplatin
alone (Hofmann et al. 1990). More research is needed to determine if quercetin
would be a useful adjunct to chemotherapy.
Duthie SJ, Collins AR, Duthie GG, Dobson VL. Quercetin and myricetin protect
against hydrogen peroxide-induced DNA damage (strand breaks and oxidised
pyrimidines) in human lymphocytes. Mutat Res. 1997;393(3):223-231.
Ferry DR, Smith A, Malkhandi J, et al. Phase I clinical trial of the
flavonoid quercetin pharmacokinetics and evidence for in vivo tyrosine kinase
inhibition. Clin Cancer Res. 1996;2(4):659-668.
Frolov VM, Peresadin NA, Khomutianskaia NI, Pshenichnyi I. The efficacy of
quercetin and tocopherol acetate in treating patients with Flexner's dysentery
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Gross M, Pfeiffer M, Martini M, Campbell D, Slavin J, Potter J. The
quantitation of metabolites of quercetin flavonols in human urine. Cancer
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Haas EM. Staying Healthy with Nutrition. Berkley, Calif: Celestial
Arts Publishing; 1992:272, 882-884.
Hofmann J, Fiebig HH, Winterhalter BR, Berger DP, Grunicke H. Enhancement of
the antiproliferative activity of cis-diamminedichloroplatinum (II) by
quercetin. Int J Cancer. 1990;45(3):536-539.
Hollman PC, Van Trijp JM, Mengelers MJ, De Vries JH, Katan, MB.
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Knekt P, Jarvinen R, Reunanen A, Maatela J. Flavonoid intake and coronary
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Murray MT, Pizzorno JE. Encyclopedia of Natural Medicine. 2nd ed.
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Scambia G, Ranelletti FO, Benedetti Panici P, et al. Quercetin potentiates
the effect of adriamycin in a multi-drug-resistant MCF-7 human breast-cancer
cell line: P-glycoprotein as a possible target. Cancer Chemother
Shils ME, Olson JA, Shike M, Ross AC. Modern Nutrition in Health and
Disease. 9th ed. Baltimore, Md: Williams & Wilkins; 1999:1274-1277.
Werbach MR. Nutritional Influences on Illness. 2nd ed. Tarzana, Calif:
Third Line Press; 1993:179, 259, 267, 389.
Young JF, Nielsen SE, Haraldsdottir J, et al. Effect of fruit juice intake on
urinary quercetin excretion and biomarkers of antioxidative status. Am J Clin
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Copyright © 2000 Integrative Medicine
CommunicationsThis publication contains
information relating to general principles
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