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. ^ Quercetin may also block other substances involved with allergies. ^ 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 urination and is sometimes called chronic pelvic pain syndrome. Conventional treatment for this condition is often unsatisfactory. One small double-blind, placebo-controlled study has found preliminary evidence that quercetin might help (see next section ). ^ Another small, double-blind, placebo-controlled trial found that a supplement containing quercetin reduced symptoms of interstitial cystitis . ^ As noted above, it has been suggested that quercetin’s antioxidant properties might make it helpful for preventing heart disease and strokes . ^ ^ ^ ^ However, the evidence that it works is highlyincomplete. Keep in mind that other powerful antioxidants such as vitamin E and beta-carotene have been ineffective for preventing these conditions. There is limited evidence, however, from a single, small double-blind trial that quercetin might have the separate effect of lowering blood pressure when it is high. ^ Test tube studies and animal research additionally suggest that quercetin might have cancer preventive properties. ^ ^ ^ ^ An animal study found that quercetin might protect rodents with diabetes from forming cataracts . ^ Another intriguing finding from test-tube research is that quercetin seems to prevent a wide range of viruses from infecting cells and reproducing once they are inside cells. One study found that quercetin produced this effect against Herpes simplex , polio virus, and various respiratory viruses, including influenza . ^ However, such studies are too indirect to tell us whether humans taking quercetin supplements can hope for benefits against diseases caused by those viruses.