Quercetin, King of the Flavonoids, a Natural Anti-allergic Substance

quercetin king of flavonoids anti-allergic

The old saying, “An apple a day, doctors go away”, has new evidence. Apples, and a number of other colorful fruits and vegetables, contain a rich amount of a powerful antioxidant called quercetin.


Quercetin is a flavonol, a subtype of potent substances called flavonoids that naturally occur in plants and offer a variety of health benefits to humans. As king of flavonoids, Quercetin is often found in rinds, young shoots, and barks of plants, and is one of the most abundant flavonoids in our diets. Onions have the highest known quercetin content (200-600 mg/kg, depending on the type and color), with fruits in a close second at between 200 to 250 mg/kg.

Some common foods with significant levels of quercetin include: onions, garlics, apples, broccoli, grapes, spinach, strawberries, tea, tomatoes. However, for therapeutic purpose, sometimes you may have to take a supplement to get high dosage.

Health Benefits

Quercetin has many potent biological properties: antioxidant, anti-inflammatory, antihistamine, antiviral, immune-boosting, etc. Since late 1970, many animal studies and a few human clinical have shown that quercetin works in multiple ways to help prevent or alleviate the symptoms of some conditions including:

Allergic conditions

Some research shows that quercetin can prevent certain immune cells from releasing histamine, the chemical that triggers an allergic reaction, as well as antigen-specific antibodies (IgE) involved in allergic responses to seasonal allergens. Quercetin may be effectively utilized in treatment of ate-late-phase bronchial asthma responses, allergic rhinitis, hay fever, eczema, and peanut-induced anaphylactic reactions.


In a double-blind, placebo-controlled clinical trial of 30 men with prostatitis (inflammation of the prostate). Participants were given either placebo or 500 mg of Quercetin twice daily. Those who received quercetin experienced a statistically significant improvement in symptoms, but those given placebo did not improve. It may also help treat rheumatoid arthritis (RA).

Interstitial Cystitis

For people experiencing bladder pains from infections (causing an urgent need to urinate, swelling and burning), quercetin could help. In a 6-week double-blind, placebo-controlled study, 20 people received either placebo or a supplement containing quercetin and other bioflavonoids. The results appeared to indicate better results in the quercetin group.

Heart Disease

Due to quercetin’s ability to lower inflammation and oxidative stress, it seems to be beneficial for people with heart and blood vessel-related disorders. Another trial indicates that quercetin might have the separate effect of lowering blood pressure when it is high.

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Nutrition Notes

Which form of  quercetin is the best?

There are two forms of quercetin supplement on market: free form (the label may simply say “quercetin”), or quercetin dihydrate (quercetin molecule is bound to two molecules of water), with the latter having better bioavailability. Neither form is water soluble. It is better to be taken with meals containing fats and oils.

In natural food, quercetin is attached to sugar molecule and appears to be absorbed better.

What dosage is recommended?

A typical dosage is 200 to 400 mg twice daily. In some formulations, quercetin is used together with nettle, bromelain, vitamin C to enhance synergy.

Is it safe to take quercetin?

Quercetin appears to be safe. However, we do not recommend use by young children, pregnant or nursing women, people with low blood pressure, or people with serious liver or kidney disease.

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