Bioflavonoids: Overview

Bioflavonoids are color-producing pigments found in plants.  Bioflavonoids such as Quercetin, Rutin, and Hesperidin are vital through their ability to increase the strength of the capillaries (blood vessels) and to regulate their permeability.  They assist Vitamin C in keeping collagen, the intercellular "cement" in healthy condition; are essential for the proper absorption and use of vitamin C; prevent Vitamin C from being destroyed in the body by oxidation; are beneficial in hypertension; help hemorrhages and ruptures in the capillaries and connective tissues and build a protective barrier against infections.

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Bioflavonoids are a special class of plant polyphenolic compounds.  Being found in high concentrations in many fruits, they are responsible for much of the coloring in such things as grapes, blueberries, and cherries.  They are also found in fairly high concentrations in citrus fruits as well.  Historically, Bioflavonoids were first described as "vitamin P" due to their ability to reduce capillary permeability.  Since then their status as a vitamin has been dropped, but the research and use of various bioflavonoids has only increased.  Some important bioflavonoids include quercetin, rutin, hesperidin, and the OPCs found in grapes, bilberries, and pine bark extractions to name a few.


Quercetin is widely distributed in plants including Oak trees (Quercus spp.), onions (Allium cepa) and tea (Camellia sinensis).  Quercetin is obtained from buckwheat and citrus fruits.  Yellow onions also contain high levels of quercetin.

Rutin is widely distributed throughout the plant kingdom.  It is used in a variety of supplement products where the addition of flavonoids is warranted.

Quercetin is available in powder and capsule form.  Bioflavonoid mixtures are often used in supplements to enhance the effect of vitamins, especially vitamin C.

Hesperidin is found primarily in the rinds of lemon and sweet oranges (Citrus sinensis).  It is not all that commonly used as a supplement ingredient, but is still used in combination with vitamin C products or combined with ingredients as a synergist for a variety of conditions.

Function; Why it is Recommended

Bioflavonoids are antioxidants and reduce blood cell stickiness and decrease bleeding from small, fragile vessels.

Rutin is a flavonoid glycoside with quercetin as the flavonoid portion and rutinose as the sugar portion.  Rutin was included as one of the original "vitamin P" substances because of its ability to decrease capillary permeability and fragility.  Like quercetin, rutin is a biologically active flavonoid.  It has been shown to have antiedemic, antiatherogenic, antiinflammatory and hypotensive properties.

Among the flavonoids, Quercetin is one of the most biologically active.  Quercetin is the aglycone (non-carbohydrate portion of a glycoside molecule) of rutin, quercetin and other glycoside flavonoids.  Quercetin is an especially potent antioxidant with some anti-inflammatory properties.  It appears to stabilize the membranes of the mast cells that release histamine.

Quercetin has been shown to have an effect on a variety of biological systems, mostly through its interaction with calmodulin, a calcium regulating protein.  One of the best studied effects of quercetin is its ability to prevent mast cells from de-granulating during an allergic response.  In preventing mast cell de-granulation, quercetin prevents the release of histamine, one of the major triggers to the overall allergic response.  Through similar actions, quercetin can act as an anti-inflammatory agent.

As a flavonoid, quercetin is able to stabilize membranes.  This is not only true of free-floating blood cells, but also capillary and arterial walls.  These activities are due to the ability of quercetin to act as a potent antioxidant as well as an inhibitor to the enzyme hyaluronidase (an enzyme that breaks down connective tissue).  The benefits of quercetin are becoming well known, and purified quercetin should become more popular in years to come.  The absorption of quercetin is limited, and studies have shown that the enzyme bromelain is capable of increasing the intestinal absorption of quercetin.  Quercetin is listed in the National Formulary and can be purchased N.F.

Rutin aids in the elimination of cholesterol in the body and helps the body to develop greater elasticity of the arterial walls to promote greater blood flow and protect the capillaries.

Hesperidin is a molecule which contains hesperetin (a bioflavonoid molecule) and the disaccharide rutinose.  It performs antioxidant actions as well as having potent anti-allergy, anti-inflammatory and anti-viral properties.  It works with vitamin C for the promotion of vascular tissue strength.  No longer considered a vitamin, Hesperidin and other bioflavonoids are now known to have many beneficial effects such as improving the effectiveness of vitamin C, improving capillary fragility, antioxidant and free radical protection to name but a few.

Quercetin is used widely for sinus problems and aids in capillary fragility.


The recommended dose for Quercetin is 200-400mg tid.  It is best to take it before meals.

Since Quercetin's action is preventive, it's best taken daily a week or two before pollen season and continued throughout.

Side-Effects; Counter-Indicators and Warnings

No toxicity has been identified with Quercetin.  If taken in large doses, however, it can cause blood pressure to decrease.

Quercetin should be avoided during pregnancy.

Bioflavonoids can help with the following:


Allergic Rhinitis / Hay Fever

Plants high in bioflavonoids such as quercetin and curcuma (rose hips, bilberry) are especially useful because they reduce your body's production of histamines or leukotrienes (substances that cause allergy symptoms) and strengthen connective tissue.

Quercetin appears to stabilize the membranes of the mast cells that release histamine.  Since quercetin's action is preventive, it is best taken daily a week or two before pollen season and continued throughout.

Indoor Allergies

May reduce IgE formation, inhibit the release of histamine, and reduce or eliminate allergy symptoms.


Varicose Veins

Bioflavonoids may be useful because of their reported antioxidant properties, their ability to increase the strength of the capillaries, and to regulate their permeability.  Rutin, in particular, is often recommended for varicose veins.


Due to its antioxidant effect, quercetin can inhibit inflammatory processes mediated by "leukotrienes" (inflammatory agents a thousand times more powerful than histamines), hyaluronidase (collagen-destroying enzymes), and lysosomal enzymes (other promoters of localized inflammation.)

Environment / Toxicity

Heavy Metal Toxicity

Bioflavonoids are known for their ability to chelate (bond with and remove) metals from the body.


Menorrhagia (Heavy Periods)

Capillary fragility is believed to play a role in many cases of menorrhagia.  Supplementation with vitamin C and bioflavonoids has been shown to reduce menorrhagia.  As vitamin C is known to significantly increase iron absorption, its therapeutic effect could also be due to enhanced iron absorption.

Not recommended for
Pregnancy-Related Issues

Quercetin should be avoided during pregnancy.



Quercetin is being used widely for sinus problems.


Chronic Inflammation

Clinical trials have not yet examined the effects of the bioflavonoid quercetin in the treatment of inflammation.  However, several inflammation-promoting pathways are known to be inhibited by quercetin.

  • Histamine is one of the body's triggers for promoting inflammation.  Quercetin is known to reduce histamine release from some inflammatory white blood cells
  • Quercetin has been likened to the anti-inflammatory drug cromolyn sodium, which acts in a similar fashion
  • Quercetin has also been shown to prevent release of leukotrienes – prostaglandin-like substances that also cause inflammation.

Bioflavonoids help to ease inflammation in the throat and fight infection.  Take 500mg of mixed bioflavonoids three or four times a day for the first three to four days.


Poor Memory

See the Link between Poor Memory and Vitamin C.


Bioflavonoid Need

When doctors recommend supplementation, the most common amounts suggested are 1,000mg of citrus flavonoids or 400mg of quercetin, each taken three times per day.  No side-effects have been linked to the flavonoids except for catechin, which can occasionally cause reversible fever, hives and anemia from the breakdown of red blood cells.



Quercetin appears to be important in the prevention of asthma attacks.  It has been shown to inhibit histamine release from mast cells and basophils when stimulated by antigens (triggers).  In addition, quercetin has both a vitamin C-sparing effect and a direct stabilizing effect on membranes, including mast cells.  It is also an antioxidant.  Other flavones also inhibit histamine release, but to a lesser degree.

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Bioflavonoids can help prevent the following:


Hives (Urticaria)

The flavonoid quercetin inhibits the manufacture and release of histamine and other allergic compounds involved in allergies.  This suggests an as yet unproven preventative effect in managing hives.  Some types of hives will respond, while others will not.

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May be useful: may help with; may help prevent
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may help with; may help prevent
Moderately useful: often helps with
Moderately useful:
often helps with
Very useful: is highly recommended for
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is highly recommended for
Should be avoided: is NOT recommended for
Should be avoided:
is NOT recommended for
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