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 inflammation.

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 lips.

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 findings.

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 degeneration.

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 antioxidants, quercetin.

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 promise.

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.

Pediatric

• 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.

Adult

Recommended adult dosages of quercetin vary depending on the health condition being treated. The following are guidelines for some of its common uses:

• 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 of quercetin.

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 provider.

If you are currently being treated with any of the following medications, you should not use quercetin supplements without first talking to your healthcare provider.

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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