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What is it? Overview Usage Side Effects and Warnings

What is Quercetin?

Quercetin belongs to a class of water-soluble plant coloring substances called bioflavonoids. Bioflavonoids have strong antioxidant effects when they are studied in the test tube, and this is the basis for some of the health claims attached to them. However, growing evidence suggests that bioflavonoids do not in fact act as antioxidants in human beings. 1 Nonetheless, as widely available plant substances, they are considered possible semi-nutrients, substances that are not essential for life but might help promote optimal health.

Quercetin is widely marketed as a treatment for allergic conditions such as asthma , hay fever , eczema , and hives . These proposed uses are based on test-tube research showing that quercetin prevents certain immune cells from releasing histamine, the chemical that triggers an allergic reaction. 2 Quercetin may also block other substances involved with allergies. 3 However, this evidence is extremely preliminary, far too preliminary to rely upon at all. There is as yet no direct evidence that taking quercetin supplements will reduce your allergy symptoms.

A different proposed use of quercetin does have some meaningful supporting evidence: prostatitis . This condition is an inflammation or infection of the prostate gland. The condition causes chronic pain and difficulty with...

Safety Issues

Quercetin appears to be quite safe. However, concerns have been raised that, under some circumstances, it might raise cancer risk. Quercetin "fails" a standard laboratory test called the Ames test, which is designed to identify chemicals that might be carcinogenic. Nonetheless, a bad showing on the Ames test does not definitely mean a chemical causes cancer. Most other evidence suggests that quercetin does notcause cancer and may, in fact, help prevent cancer. 4 Still, one highly preliminary study suggests that quercetin combined with other bioflavonoids in the diet of pregnant women might increase the risk of infant leukemia. 5 On this basis, pregnant women should probably avoid quercetin supplements. Maximum safe dosages for young children, nursing women, or...