Quercetin and Other Bioflavonoids

We have previously discussed the bioflavonoids under Vitamin P (for permeability) in Chapter 5. They are ascorbic-acid-related substances, usually found in foods along with vitamin C, particularly in the white of the rind of citrus fruits, in buckwheat, and in vegetables such as green peppers and tomatoes. As a group, these bioflavonoids, including hesperidin, rutin, quercetin, and catechin, work to keep the capillary blood vessels strong and to reduce vascular fragility and subsequent bleeding and bruising, as well as to lower the microtrauma of tissue injuries. They have been used successfully in preventing injury and bruising in athletes and in speeding the recovery of acutely injured athletes and other performers. A mix of bioflavonoids containing hesperidin and ascorbic acid seems to have the best effect (including anti-inflammatory) in these injury conditions. Some bioflavonoids apparently act as immune supporters, antioxidants, and detoxifiers. There are a number of other uses of these interesting substances.


Catechin, one of the bioflavonoid components, appears to decrease histamine release in allergy and thus reduce symptoms. It also is a mild anti-inflammatory in rheumatoid arthritis. Furthermore, it has protective effects on the liver in response to alcohol and as a healing aid for people with hepatitis B.


Quercetin has been the subject of recent studies. It can decrease allergic reactions by several mechanisms. First, it helps to stabilize mast cells and basophils and inhibits their degranulation and subsequent release of histamine and other inflammatory chemicals. Quercetin also inhibits some inflammatory enzymes, such as lipid peroxidases, and decreases leukotriene (another inflammatory molecule) formation. Thus, quercetin may be helpful not only in allergies, but in all kinds of inflammatory responses, such as injury, bursitis, asthma, and arthritis. In rheumatoid arthritis, it has particular potential, since it decreases mast cell degranulation, one of the fundamental causes of inflammation within the joint spaces. Quercetin is further thought to decrease the infectiousness of certain RNA and DNA viruses, such as herpes, polio, and Epstein-Barr, by inhibiting their replication. It may also be helpful in preventing eye and nerve damage in diabetes by decreasing tissue irritation.


Usually, bioflavonoids are supplemented as a group in amounts of 250–500 mg., one to several times daily. Many vitamin C formulas contain bioflavonoids, particularly rutin and hesperidin. Quercetin is available in various strengths; supplementation of 100–250 mg. three times daily is probably an effective level.

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Elson M. Haas MD Written by Elson M. Haas MD

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