Vitamins, Minerals and Dietary Supplements

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.