If you've ever wondered what chemical gives fruits and flowers their vibrant colors, the answer is flavonoid compounds. Quercetin is one such pigment; it is the most abundant flavonoid and the building block for all the others. Flavonoids, which are synthesized by plants, are rich in antioxidants and have the ability to modify certain enzyme pathways. Flavonoid compounds, including quercetin, are considered semi-nutrients, meaning they are not essential to biological functions but may be beneficial to maintaining health. Quercetin is found in many fruits and it also available as a dietary supplement.
Flavonoids
Quercetin is an antioxidant responsible for collecting and neutralizing free radicals in the body. Free radicals damage cell membranes and DNA molecules, and can also cause cell death. Quercetin also shows anti-inflammatory and antihistamine properties in the lab, but scientists are not yet certain if it has the same effects in the body. Oregon State University states that evidence is mounting showing the benefits of quercetin may actually be due to their ability to modulate cellular pathways.
Dietary Sources of Quercetin
Many plants, especially fruits, contain abundant amounts of quercetin. It is found in oranges, lemons, limes, grapefruit, tangerines, apples, green tea, black tea, red wine, buckwheat and onions. Lesser amounts are found in leafy green vegetables, olive oil, blackberries, dark cherries, bilberries, blueberries, beans, cauliflower and cabbage. Quercetin is also available as a dietary supplement in the form of capsules and tablets. The University of Maryland Medical Center recommends general supplementation for adults of 100 to 240 mg three times per day or 250 to 600 mg twice a day for allergy symptoms, prostatitis or bladder infections. Quercetin chalone may be absorbed better, but there is no real evidence supporting this.
Quercetin Benefits
Quercetin is considered beneficial for chronic prostatitis, an inflammation or infection of the prostate gland, which causes painful and difficult urination and does not respond well to other forms of treatment. Quercetin is also used to reduce the symptoms of allergy and hay fever due to its antihistamine effects. It may helpful in reducing the risk for developing coronary artery disease by reducing plaque formation along artery walls and protecting against damage caused by LDL, the "bad" cholesterol, as well as lowering blood pressure. Its anti-inflammatory properties may prove helpful in rheumatoid arthritis treatment. Memorial Sloan-Kettering Cancer Center reports several small studies indicate quercetin may have significant anti-cancer properties, but more data is needed. No evidence supports its use as a performance enhancer in sports.
Precautions
Taken in daily doses of less than 1 g, quercetin is generally considered safe. Side effects of the supplement include headache, nausea and tingling in the hands and feet. Doses over 1 g have caused kidney damage, notes the University of Maryland Medical Center, so you should only take quercetin under your doctor's supervision if you have diabetes or kidney disease. Quercetin can interact with some medications including anticoagulants, corticosteroids and chemotherapy drugs. You should not take it if you are pregnant or breastfeeding.
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