Quercetin, a water-soluble chemical compound classified as a bioflavonoid, is a plant pigment responsible for giving many fruits, vegetables and flowers their vibrant color. In the laboratory, quercetin exhibits some strong anti-oxidant properties. However, its anti-oxidant properties may not be expressed in the human body in the same way they are expressed in the lab. Most of the uses of quercetin are based on laboratory findings, so more studies are needed to fully substantiate its efficacy.
Dietary Sources
Quercetin is a phytochemical and the most abundant bioflavonoid. It is found in high concentration in citrus fruits, apples, parsley, onions, green tea, black tea and red wine. It is also present in smaller amounts in cabbage, kale, dark cherries, grapes, blackberries, black currents, blueberries, olive oil, buckwheat, nuts and leafy green vegetables. Quercetin is also available as a dietary supplement in capsule and pill form. The supplement is sometimes sold with bromelain, an enzyme found in pineapples, as an anti-inflammatory supplement. Bromelain may increase the absorption of quercetin in the intestine, according to Memorial Sloan-Kettering Cancer Center. A water-soluble form of quercetin is sold as quercetin chalone, and is marketed as being more easily absorbed, though there is currently no evidence to prove this.
Benefits
The benefits of quercetin are purported to be many, although most are not backed by clinical study. Quercetin has been shown to exhibit some antihistamine effects, and may prove to be effective in treating some allergic conditions. The quercetin contained in red wine is thought to reduce the risk of developing atherosclerosis, or hardening of the arteries, by protecting the arteries from LDL cholesterol. Quercetin has also been found to be helpful in reducing pain and other symptoms of prostatitis, or inflammation of the prostate gland. Although further studies are needed, the quercetin found in fruits and vegetables may protect against certain cancers, including cancer of the breast, colon, ovaries, prostate and lung. Because of its anti-inflammatory effects, increasing the amount of fruits, vegetables, roots and nuts in the diet may alleviate some of the symptoms of rheumatoid arthritis.
Dosage
Increasing the amount of bioflavonoid-containing foods in the diet can be beneficial in preventing some cancers and atherosclerosis. The supplement is being used to reduce the symptoms of hay fever, eczema and asthma, although it shows the most promise in the treatment of interstitial cystitis and prostatitis. The University of Maryland Medical Center recommends divided doses of 100 to 150 mg per day for general supplementation, 250 to 600 mg per day for allergy symptoms and 500 mg per day for interstitial cystitis and prostatitis.
Precautions
Quercetin appears quite safe when taken in recommended dosages. The primary side effects are stomach upset and headache. Quercetin is excreted through the kidneys, so if you are diabetic, or have kidney disease, you should first discuss taking quercetin with your doctor. Quercetin is a dietary supplement and thus not rigorously tested by the FDA. Quercetin supplements should only be purchased from a reputable manufacturer.
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