Quercetin belongs to a group of plant pigments called flavonoids that are
largely responsible for the colors of many fruits, flowers, and vegetables.
Flavonoids, such as quercetin, provide many health-promoting benefits. They act
as antihistamines (which are useful in reducing allergy symptoms) and help
reduce inflammation associated with various forms of arthritis. Quercetin also
works as an antioxidant by scavenging damaging particles in the body known as
free radicals. These particles occur naturally in the body but can damage cell
membranes, interact with genetic material, and possibly contribute to the aging
process as well as the development of a number of conditions including heart
disease and cancer. Antioxidants such as quercetin can neutralize free radicals
and may reduce or even help prevent some of the damage they cause.
Quercetin offers a variety of potential therapeutic uses, primarily in the
prevention and treatment of the conditions listed below. Of note is that
quercetin seems to work better when used in conjunction with bromelain, a
digestive enzyme found in pineapples, particularly for allergies and
Allergies, Asthma, Hayfever and Hives Quercetin inhibits the
production and release of histamine and other allergic/inflammatory substances.
Histamine is a substance that contributes to allergy symptoms such as a runny
nose, watery eyes, hives, and swelling of soft tissue including the face and
Heart Disease Test tube, animal, and some population-based
studies suggest that the flavonoids quercetin, resveratrol, and catechins (all
found in high concentration in red wine) may help reduce the risk of
atherosclerosis (plaque build up in the arteries that can lead to heart attack
or stroke). By acting as antioxidants, these nutrients appear to protect against
the damage caused by LDL ("bad") cholesterol and may help prevent death from
heart disease. Additional rigorous studies in people are needed to confirm these
High Cholesterol Flavonoids, like quercetin, from red wine or
orange juice may help lower cholesterol levels.
Eye Disorders Free radicals are thought to contribute to the
development of certain eye disorders including cataracts and macular
degeneration (a disorder that leads to lens damage and possibly blindness).
Flavonoids, such as quercetin, neutralize free radicals and may play a role in
the prevention and/or treatment of these eye conditions.
In a study of 3,072 adults with symptoms of macular degeneration, moderate
red wine consumption (a source of quercetin) offered some protection against the
development and progression of the disease. Dark berries, such as blueberries,
blackberries, and dark cherries, are also high in flavonoids. Some suggest that
eating these fruits regularly may also offer benefit for preventing macular
Similarly, animal studies suggest that quercetin inhibits the activity of
compounds that contribute to the development of cataracts.
Arthritis According to laboratory and animal studies,
quercetin has anti-inflammatory properties. In test tubes, for example,
quercetin inhibits the type of inflammation that can occur in the joints of
those with arthritis. In addition, there are reports of people with rheumatoid
arthritis who experienced an improvement in their symptoms when they switched
from a typical Western diet to a vegan diet with lots of uncooked berries,
fruits, vegetables, nuts, roots, seeds, and sprouts containing, amongst other
Fibromyalgia Similar to the case reports for arthritis, people
with fibromyalgia who switched from a typical Western diet to a vegan diet high
in flavonoids such as quercetin experienced improvement in their symptoms.
Prostate Health Some studies suggest that quercetin improves
pain and other symptoms in men with chronic prostatitis (inflammation of the
prostate). In addition, preliminary laboratory studies indicate that quercetin
may inhibit the growth of prostate cancer cells in test tubes. How this will
ultimately translate to prevention or treatment of prostate cancer in men is
unknown at this time.
Cancer Quercetin and other flavonoids from fruits and
vegetables have long been considered important substances to possibly help
prevent cancer. New laboratory studies are suggesting that this belief may be
accurate. Quercetin and other flavonoids have been shown in animal and test tube
studies to inhibit the growth of cancer cells, including those from breast,
colon, prostate, and lung tumors.
One study evaluating quercetin in humans included 11 people with various
forms of cancer. This study found that quercetin reduced the actual tumor size
in two people and inhibited the activity of a protein that plays a role in tumor
growth in nine of the 11 people. More studies are needed to further explore the
possible beneficial effects of quercetin in people.
Researchers are also hopeful that quercetin and other flavonoids may prove to
enhance the action of anti-cancer drugs. This issue, however, of using
anti-oxidants at the same time as chemotherapy or radiation to treat cancer is
controversial. Until more is know, it should likely be avoided.
Canker Sores Quercetin may reduce the frequency of mouth sores
and produce mild symptomatic relief.
Other Researchers have been evaluating medicinal plants in the
Democratic Republic of Congo that have been used traditionally to treat diarrhea
and dysentery. What they have found is that flavonoids, such as quercetin, are
among the active ingredients in these plants. Studies in Russia regarding the
use of quercetin, along with other supplements and/or conventional medications,
to treat dysentery caused by infections such as Shigella have shown some
Fruits and vegetables -- particularly citrus fruits, apples, onions, parsley,
tea, and red wine -- are the primary dietary sources of quercetin. Olive oil,
grapes, dark cherries, and dark berries, such as blueberries, blackberries, and
bilberries are also high in flavonoids including quercetin.
Quercetin supplements are available in several strengths in powder or capsule
form. They are often packaged with bromelain (an enzyme found in pineapple) as
an anti-inflammatory agent. Bromelain exerts anti-inflammatory and anti-allergy
activity of its own and also increases the absorption of quercetin. Other
flavonoid-rich extracts include those from grape seed, bilberry, Ginkgo
biloba, and green tea.
How to Take It
Allergies: The recommended adult dose should be adjusted to account
for the child's weight. Most adult dosages are calculated on the basis of a 150
lb (70 kg) adult. Therefore, if the child weighs 50 lb (20 to 25 kg), the
appropriate dose of quercetin for this child would be 1/3 of the adult dosage.
Recommended adult dosages of quercetin vary depending on the health condition
being treated. The following are guidelines for some of its common
General supplementation: 100 to 250 mg three times per day.
Allergy symptoms: 250 to 600 mg per day divided in several doses
Chronic hives: 200 to 400 mg of quercetin three times daily, taken
approximately 20 minutes before each meal
If used with bromelain, the amount of bromelain should be equal to the amount
No adverse effects from the use of quercetin have been reported. However,
because supplements may have side effects or interact with medications, they
should be taken only under the supervision of a knowledgeable healthcare
If you are currently being treated with any of the following medications, you
should not use quercetin supplements without first talking to your healthcare
Chemotherapy Test tube and animal studies suggest that
quercetin may enhance the effects of doxorubicin and cisplatin, two chemotherapy
medications used to treat cancer. More research is needed to determine if
quercetin has any application to people being treated with either of these
agents. In addition, use of antioxidants at the same time as chemotherapy is
somewhat controversial. Therefore, more research is needed before conclusions
about safety and effectiveness can be drawn.
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Review Date: April 2002
Reviewed By: Participants in the review process include: Jacqueline A. Hart, MD,
Department of Internal Medicine, Newton-Wellesley Hospital, Harvard University
and Senior Medical Editor Integrative Medicine, Boston, MA; Gary Kracoff, RPh
(Pediatric Dosing section February 2001), Johnson Drugs, Natick, Ma; Steven
Ottariono, RPh (Pediatric Dosing section February 2001), Veteran's
Administrative Hospital, Londonderry, NH; Margie Ullmann-Weil, MS, RD,
specializing in combination of complementary and traditional nutritional
therapy, Boston, MA. All interaction sections have also been reviewed by a team
of experts including Joseph Lamb, MD (July 2000), The Integrative Medicine
Works, Alexandria, VA;Enrico Liva, ND, RPh (August 2000), Vital Nutrients,
Middletown, CT; Brian T Sanderoff, PD, BS in Pharmacy (March 2000), Clinical
Assistant Professor, University of Maryland School of Pharmacy; President, Your
Prescription for Health, Owings Mills, MD; Ira Zunin, MD, MPH, MBA (July 2000),
President and Chairman, Hawaii State Consortium for Integrative Medicine,
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