Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit.
Who is likely to be deficient?
No clear deficiency of quercetin has been established.
How much is usually taken?
Some doctors recommend 200–500 mg of quercetin taken two to three times per day.
Optimal intake remains unknown.
Are there any side effects or interactions?
No clear toxicity has been identified. Early quercetin research suggested that large
amounts of quercetin could cause cancer in animals.1 Most,234 but not all,5 current research finds quercetin to be safe or actually
linked to protection from cancer.
Quercetin has been shown to cause chromosomal mutations in certain bacteria in test tube
studies.6 Although the significance of this finding for humans is not clear, some
doctors are concerned about the possibility that
birth defects could occur in the offspring of people supplementing with quercetin at the
time of conception or during pregnancy.
Since flavonoids help protect and enhance
vitamin C, quercetin is often taken with
vitamin C.
Are there any drug
interactions?
Certain medicines may interact with quercetin. Refer to drug interactions for a list of those medicines.
References (To view, roll mouse over the "References" heading; to hide, click on the heading)
1. Ishikawa M, Oikawa T, Hosokawa M, et al. Enhancing effect of quercetin
on 3-methylcholanthrene carcinogenesis in C57B1/6 mice. Neoplasma
1985;43:435–41.
2. Hertog MGL, Feskens EJM, Hollman PCH, et al. Dietary flavonoids and
cancer risk in the Zutphen elderly study. Nutr Cancer 1994;22:175–84.
3. Castillo MH, Perkins E, Campbell JH, et al. The effects of the
bioflavonoid quercetin on squamous cell carcinoma of head and neck origin. Am J Surg
1989;351–5.
4. Stavric B. Quercetin in our diet: from potent mutagen to probably
anticarcinogen. Clin Biochem 1994;27:245–8.
5. Barotto NN, López CB, Eyard AR, et al. Quercetin enhances
pretumourous lesions in the NMU model of rat pancreatic carcinogenesis. Cancer Lett
1998;129:1–6.
6. Stoewsand GS, Anderson JL, Boyd JN, Hrazdina G. Quercetin: a mutagen,
not a carcinogen in Fischer rats. J Toxicol Environ Health 1984;14:105–14.
The information presented in Aisle7 is for informational purposes only.
It is based on scientific studies (human, animal, or in vitro), clinical experience,
or traditional usage as cited in each article. The results reported may not necessarily occur
in all individuals. For many of the conditions discussed, treatment with prescription or over
the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist
for any health problem and before using any supplements or before making any changes in
prescribed medications.
