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Quercetin
What is quercetin? Why do we need it?
Quercetin is a flavanoid, a substance found in fruits, flowers
and vegetables. Among other things, flavanoids give objects
their color. Most flavanoids have been found to work as both
antioxidants and anti-inflammatories, which are useful in
treating or preventing a variety of health problems.
Quercetin is effective in reducing allergic reactions and
may be beneficial in treating canker sores, hives, asthma
and other inflammatory responses. Other conditions for which
quercetin may be helpful include diabetes, dysentery, gout,
cataracts, and atopic dermatitis.
Recent research has focused on quercetin’s ability to
fight certain forms of cancer. In one study, it helped prevent
the formation of skin cancer. In another, it was effective
against the formation of tumors in patients with ovarian cancer
and hepatoma.
How much quercetin should I take?
Most health practitioners recommend 100-250 milligrams of
quercetin daily as a general supplement. For other conditions,
the dosage can be increased:
For lowered histamine levels and allergy symptoms: 250-600
mg.
For treatment of gout: 200-400 mg of quercetin taken with
bromelain between meals.
For treatment of chronic hives: 200-400 mg of quercetin taken
approximately 20 minutes before each meal.
What are some good sources of quercetin?
Quercetin can be found in fruits and vegetables (particularly
citrus fruits), apples, onions, parsley, green tea and red
wine. Flavonoid rich extracts, such as those from grape seed,
bilberry and ginkgo biloba, are also good sources of quercetin.
What can happen if we don't get
enough quercetin?
No side-effects have been reported concerning quercetin deficiency.
What can happen if I take too much?
Are there any side-effects I should be aware of?
No side effects have been associated with quercetin. No problems
with excess amounts of quercetin have been documented.
For more information on quercetin, please consult your health
care provider.
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References
• Duthie SJ, Collins AR, Duthie
GG, Dobson VL. Quercetin and myricetin protect against hydrogen
peroxide-induced DNA damage (strand breaks and oxidized pyrimidines)
in human lymphocytes. Mutat Res 1997;393(3):223-231.
• Frolov
VM, Peresadin NA, Khomutianskaia NI, Pshenichnyi I. The efficacy
of quercetin and tocopherol acetate in treating patients with
Flexner's dysentery [in Ukrainian]. Lik Sprava 1993;4:84-86.
• Gross M, Pfeiffer M, Martini
M, Campbell D, Slavin J, Potter J. The quantitation of metabolites
of quercetin flavonols in human urine. Cancer Epidemiol
Biomarkers Prevent 1996;5(9):711-720.
• Hollman PC, Van Trijp JM, Mengelers MJ, De Vries
JH, Katan, MB. Bioavailability of the dietary antioxidant
flavonol quercetin in man. Cancer Lett 1997;114(1-2):139-140.
• 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 Nutr
1999;69(1):87-94.
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