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QUERCITIN

You may have heard of the "French paradox." The French diet is very high in saturated fat and cholesterol (just think of pate de fois gras and croissants), yet France has one of the world's lowest rates of heart disease. One theory for this apparent discrepancy is that another major player in the French diet—red wine—protects the arteries of the heart.

Quercetin is a natural antioxidant found in red wine. Antioxidants protect cells in the body from damage by free radicals, naturally occurring but harmful substances that are thought to play a role in cardiovascular disease. On this basis, it has been suggested that quercetin might help protect against heart attacks as well as strokes.

Quercetin belongs to a class of water-soluble plant coloring substances called bioflavonoids. Although they don't seem to be essential to life, it's possible that we need bioflavonoids for optimal health.

Another intriguing finding is that quercetin may help prevent immune cells from releasing histamine, the chemical that initiates the itching, sneezing, and swelling of an allergic reaction. Based on this very preliminary research, quercetin is often recommended as a treatment for allergies and asthma.

Sources

Quercetin is not an essential nutrient. It is found in red wine, grapefruit, onions, apples, black tea, and, in lesser amounts, in leafy green vegetables and beans. However, to get a therapeutic dosage, you'll have to take a supplement.

Quercetin supplements are available in pill and tablet form.

Therapeutic Dosages

A typical dosage is 200 to 400 mg 3 times daily. A special type of quercetin, quercetin chalcone, is claimed to have better absorption, but there is little reliable evidence to prove this.

Therapeutic Uses

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.1,2 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 as 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).4

Another small double-blind placebo-controlled trial found that a supplement containing quercetin reduced symptoms of interstitial cystitis.5

As noted above, it has been suggested that quercetin’s antioxidant properties might make it helpful for preventing heart disease and strokes.6–10 However, the evidence that it works is highly incomplete. Keep in mind that other powerful antioxidants such as vitamin E and beta-carotene have been ineffective for preventing these conditions.

Test tube studies and animal research additionally suggest that quercetin might have cancer preventive properties.11–15

An animal study found that quercetin might protect rodents with diabetes from forming cataracts.16 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.17,18 However, such studies are too indirect to tells us whether humans taking quercetin supplements can hope for benefits against diseases caused by those viruses.

What is the Scientific Evidence for Quercetin?

Prostatitis
A 1-month double-blind placebo-controlled trial of 30 men with chronic pelvic pain (prostatitis) tested the potential effectiveness of quercetin.4 Participants received either placebo or 500mg of the supplement twice daily. The results showed that people who received quercetin experienced a statistically significant improvement in symptoms (such as pain), but those given placebo did not improve.

While these are promising results, the study was small and cannot be regarded as definitive. Furthermore, researchers failed to provide the usual statistical evaluation required for such studies (a statistical analysis that directly compares the results in the treatment group against those in the placebo group). Thus, further study will be necessary to discover whether quercetin is actually effective for prostatitis.

Interstitial Cystitis
People with interstitial cystitis experience pain and discomfort in the bladder that is reminiscent of a bladder infection, but without the actual presence of such an infection. In a 6-week double-blind study, 20 people received either placebo or a supplement containing quercetin and other bioflavonoids.5 The results appeared to indicate better results in the quercetin group. However, this study has only been presented as an abstract and it is not clear from the writeup whether the results were statistically meaningful.

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