Flavonoids were discovered by Nobel Prize-winning biochemist Albert Szent-Gyorgi, who labeled them "vitamin P". He discovered that they enhanced the function of vitamin C, improving absorption and protecting it from oxidation. Flavonoids that have been shown to have particularly beneficial properties include proanthocyanidins, green tea polyphenols and soy isoflavones. Quercetin and its derivatives; the citrus bioflavonoids, including quercitrin, rutin and hesperidin; have also been fairly well studied.

What they do in the body

Cardiovascular system

Flavonoids are important for blood vessel health. They regulate capillary permeability, thereby stopping fluid, protein and blood cells from seeping out while still allowing oxygen, carbon dioxide and other nutrients to pass through. Many flavonoids enhance capillary strength, preventing them from being easily bruised. This is partly due to the vitamin C-enhancing action of flavonoids. This may help protect against infection and blood vessel diseases.

FlavonoidsFlavonoids can also relax the smooth muscle of the cardiovascular system, thus lowering blood pressure. This also improves circulation to the heart itself. Flavonoids are antioxidant and can also prevent oxidation of harmful LDL cholesterol, thereby preventing the build-up of atherosclerotic plaque. They may also stop blood platelets from clumping together which can help to reduce blood clotting and damage to blood vessels.

Anti-inflammatory effects

Flavonoids have anti-inflammatory properties. This is due to their antioxidant effects and to their ability to act against histamines and other mediators of inflammation, such as prostaglandins and leukotrienes.

Other effects

While flavonoids have many properties in common, specific compounds often have specific properties. Some may have estrogen-like activity while others inhibit tumor growth.


Flavonoids are usually easily absorbed from the intestine. Excesses are excreted in the urine.


There are no reports of flavonoid deficiencies as most people seem to get enough in their diet to prevent this. It is possible, however, that many people do not eat enough for optimal health.

Recommended intakes

There are no recommended intakes for flavonoids.


Bioflavonoid supplements are available in varying types and doses. Pine bark and grape seed extracts are sources of proanthocyanidins. The mix of these flu vonoids, like other nutrients, varies from plant species to species. Both sources cun be used interchangeably, but grape seed extract may have an advantage over pine bark. Most grape seed extracts contain 92 to 95 per cent proanthocyanidins, whereas pine bark extracts usually contain from 80 to 85 percent. Grape seed extract also contains small quantities of a beneficial flavonoid found in green tea.

Toxic effects

There are no known toxic effects of large intakes.

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