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Other common
name(s): quercetine, sophretin, meletin
Scientific/medical
name(s): 3,3',4',5,7-pentahydroxyflavone
Description
Quercetin is a type of plant-based chemical, or phytochemical,
known as a flavonoid (see also Phytochemicals).
Good sources include apples, onions, teas, red wines, and many other
foods. Quercitin is also available as a dietary supplement.
Overview
Quercetin appears to have anti-inflammatory and antioxidant
properties. It has been promoted as being effective against a wide
variety of diseases, including cancer. While some early laboratory
results appear promising, as of yet there is no reliable clinical
evidence that quercetin can prevent or treat cancer in humans.
How is it promoted for use?
Quercetin is said to have a number of uses, but most of these
are based on early findings from laboratory studies. Some early studies
have suggested quercetin has antihistamine properties, and it is often
promoted to help control allergies and asthma. Some proponents claim it
can help stabilize small blood vessels and may help protect against
heart attacks and strokes.
Quercetin is sometimes promoted to help prevent or treat
different types of cancer. It has also been promoted to help with the
symptoms of chronic prostatitis (swelling of the prostate gland) and to
relieve some of the neurologic complications of diabetes.
What does it involve?
Quercetin is a common chemical pigment in the rinds and barks
of a wide variety of plants. It is one of the main flavonoids in the
diet, and is found in large amounts in apple skins, onions, tea, and
red wine. It is also found in leafy green vegetables, berries, and in
herbs such as ginkgo and St. John's wort.
Quercetin is available in higher amounts in dietary
supplements than would typically be found in food sources. Supplements
are sold as capsules or tablets ranging in doses from 50 milligrams
(mg) to 500 mg. There is no recommended standard dose for quercetin.
What is the history behind it?
Plants containing flavonoids have a long history of use in
traditional medicines in many cultures, but flavonoids themselves were
not discovered until the 1930s. Quercetin first gained attention
several decades ago when it was found to cause DNA mutations in
bacteria, a sign that it might actually contribute to causing cancer.
Animal research done since that time has been inconclusive, and what
little evidence there is in humans does not seem to support this idea.
Research in recent years has focused on several possible helpful
effects of quercetin, including its potential role in preventing
cancer.
What is the evidence?
Most of the research on quercetin and cancer has been done in
cell culture or animal studies. These types of studies can suggest
possible helpful effects, but they do not provide proof that such
effects can be achieved in humans. It is still unclear how well
quercetin is absorbed by the human body when taken by mouth. Controlled
clinical trials are needed to show whether quercetin has helpful
properties in humans.
Studies done in cell cultures have shown that quercetin has
activity against some types of cancer cells. This may be due to its
antioxidant or anti-inflammatory properties, or it may be due to other
mechanisms. Recent studies suggest that quercetin can slow the growth
of cancer cells and can help foster apoptosis, a form of natural cell
death that doesn't happen in most cancer cells. Some studies in animals
have shown that quercetin may help protect against certain types of
cancer, particularly colon cancer.
Studies in humans have mainly been population-based and have
focused on the role of flavonoids in the diet as a group as opposed to
quercetin in particular. These types of studies are not as conclusive
as clinical trials. They cannot prove cause and effect but often
suggest links that can then be tested in clinical trials. While some of
these population-based studies have found that people with diets high
in flavonoids may have lower risk of breast, lung, pancreatic, and
other types of cancer, it is not clear what role quercetin played in
their findings. One clinical study of people with a strong inherited
tendency to develop colorectal cancer found that the combination of
quercetin and curcumin supplements decreased the number and size of
precancerous rectal tumors. No other clinical trials testing
quercetin's ability to prevent or treat cancer have been reported in
the medical literature. Clinical trials are needed to further clarify
quercetin's possible benefits.
In addition to cancer prevention and treatment, preliminary
studies have also suggested potential value for quercetin in
prostatitis (inflamed prostate) and heart disease. Further studies are
needed before any recommendations can be made.
Until conclusive clinical research findings emerge, it is
reasonable to include foods that contain quercetin as part of a
balanced diet with an emphasis on fruits, vegetables, legumes, and
whole grains. The interaction between certain phytochemicals and the
other compounds in foods is not well understood, but it is unlikely
that any single compound offers the best protection against cancer. A
balanced diet that includes 5 or more servings a day of fruits and
vegetables, along with foods from a variety of other plant sources such
as nuts, seeds, whole grain cereals, and beans, is likely to be more
effective in reducing cancer risk than eating one particular
phytochemical in large amounts.
Are there any possible problems or
complications?
This product is sold as a
dietary supplement in the United States. Unlike drugs (which must be
tested before being allowed to be sold), the companies that make
supplements are not required to prove to the Food and Drug
Administration that their supplements are safe or effective, as long as
they don't claim the supplements can prevent, treat, or cure any
specific disease.
Some such products may not
contain the amount of the herb or substance that is written on the
label, and some may include other substances (contaminants). Actual
amounts per dose may vary between brands or even between different
batches of the same brand.
Most such
supplements have not been tested to find out if they interact with
medicines, foods, or other herbs and supplements. Even though some
reports of interactions and harmful effects may be published, full
studies of interactions and effects are not often available. Because of
these limitations, any information on ill effects and interactions
below should be considered incomplete.
Quercetin in the amounts consumed in a healthy diet is
unlikely to cause any major problems. There have been some occasional
reports of nausea when supplements are taken in high doses. Quercetin
supplements have not been studied for safety in women who are pregnant
or breast-feeding. Relying on this type of treatment alone and avoiding
or delaying conventional medical care for cancer may have serious
health consequences.
Additional Resources
More information from your American Cancer
Society
The following information on complementary and alternative
therapies may also be helpful to you. These materials may be found on
our Web site (www.cancer.org)
or ordered from our toll-free number (1-800-ACS-2345).
References
Adebamowo CA, Cho E, Sampson L, et al. Dietary flavonols and
flavonol-rich foods intake and the risk of breast cancer. Int J Cancer.
2005;114:628-633.
Bosetti C, Spertini L, Parpinel M, et al. Flavonoids and
breast cancer risk in Italy. Cancer
Epidemiol Biomarkers Prev. 2005;14:805-808.
Cruz-Correa M, Shoskes DA, Sanchez P, et al. Combination
treatment with curcumin and quercetin of adenomas in familial
adenomatous polyposis. Clinical
Gastroenterology & Hepatology. 2006;4:1035-1038.
Hubbard GP, Wolffram S, de Vos R, Bovy A, Gibbins JM,
Lovegrove JA. Ingestion of onion soup high in quercetin inhibits
platelet aggregation and essential components of the
collagen-stimulated platelet activation pathway in man: a pilot study. British Journal of Nutrition
2006;96:482-488.
Kim YH. Lee YJ. TRAIL apoptosis is enhanced by quercetin
through Akt dephosphorylation. Journal
of Cellular Biochemistry. 2007;100:998-1009.
Nöthlings U, Murphy SP, Wilkens LR, Henderson BE,
Kolonel LN. Flavonols and pancreatic cancer risk: the multiethnic
cohort study. Am J
Epidemiol. 2007;166:924-931.
Memorial Sloan-Kettering Cancer Center. About herbs:
Quercetin. 2005. Accessed at: http://www.mskcc.org/mskcc/html/69346.cfm
on June 10, 2008.
PDRhealth. Quercetin. Accessed at:
www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/que_0219.shtml
on June 10, 2008.
Schabath MB, Hernandez LM, Wu X, Pillow PC, Spitz MR. Dietary
phytoestrogens and lung cancer risk. JAMA.
2005;294:1493-1504.
Shoskes DA, Zeitlin SI, Shahed A, Rajfer J. Quercetin in men
with category III chronic prostatitis: A preliminary prospective
double-blind, placebo-controlled trial. Urology. 1999;
54:960-963.
Volate SR, Davenport DM, Muga SJ, Wargovich MJ. Modulation of
aberrant crypt foci and apoptosis by dietary herbal supplements
(quercetin, curcumin, silymarin, ginseng and rutin). Carcinogenesis.
2005;26:1450-1456.
Note: This information may not cover
all possible claims, uses, actions, precautions, side effects or
interactions. It is not intended as medical advice, and should not be
relied upon as a substitute for consultation with your doctor, who is
familiar with your medical situation.
Last Medical Review: 11/01/2008
Last Revised: 11/01/2008
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