Flavonoids

Anthocyanins, bioflavonoids, cha/ones, flavones, flavanols, flavonones, isoflavonoids

Plants contain compounds called flavonoids that give them their characteristic colors and hues. The term “flavonoid” is derived from the Latin word “flavus” which means “yellow,” for one of the colors seen in some higher orders of plant species.

The presence of flavonoids was first detected in the 1930s by Albert Szent-Gyorgi, a Hungarian-born American biochemist. Szent-Gyorgi won a Nobel prize in medicine for his pioneering work on vitamin C. He originally named flavonoids “vitamin P.” One of the first substances that Szent-Gyorgi found containing a flavonoid was in the rinds of citrus fruits, which he named citrin. He found that combining citrin with vitamin C enhanced its absorption and strengthened vitamin C’s antioxidant properties. He also discovered that this compound helped strengthen blood vessels, especially the capillaries, and aided in the prevention of capillary fragility. Although not considered essential in the same manner as vitamins, flavonoids play a major role in health maintenance.

Flavonoids are found in a wide range of foods, including citrus, soy, green tea, tomatoes, apples, and grapes. Over 4,000 flavonoids have been identified to date.

Reported uses

Flavonoids can be considered antioxidants, which are compounds that guard against the destructive forces produced by substances known as free radicals. Free radicals are molecules that lack electrons, which makes them unstable; such molecules try to stabilize themselves by stealing an electron from nearby molecules, thereby rendering stable molecules unstable and causing radical change to the cell. This mutation of the cell has now been linked to such conditions as cancer, arthritis, blood transport disorders, cardiovascular disease, and allergies. The bulk of the research has focused on the properties and efficacy of bilberry, green tea, oligomeric proanthocyanidins (OPCs), quercetin, and soy.

Bilberry

Bilberry (Vaccinium myrtillus), also known as European blueberry, contains potent flavonoids known as anthocyanosides. These compounds help to stabilize connective tissue by increasing the integrity of the collagen matrix and the production of collagen, and by preventing the destruction of collagen connective tissue around blood vessels. Collagen is a fibrous structural protein that can be found in all parts of the body. It’s also dispersed in the vitreous liquid of the eye to form a gel that helps maintain the proper stiffness and shape of the eye. The antioxidant effects of bilberry can be seen when it’s used in the treatment of ophthalmic disorders such as glaucoma and night blindness. In glaucoma, bilberry increases the tensile strength and integrity of the collagen, which may decrease intraocular pressure. Night blindness may also be helped by bilberry’s anthocyanosides, which speed up the regeneration of the rods in the retina of the eye. The rods help with night vision and low light adaptation.

Green tea

Green tea contains flavonoids and antioxidants called polyphenols, which may guard against progression of certain cancers. It’s suggested that green tea’s antimutagenic and anticarcinogenic characteristic may be based on its action of blocking cell membrane receptors and suppressing nitrosamine production.

Green tea may also lower total cholesterol levels and LDL cholesterol oxidation. It may not be appropriate for certain patients because it contains caffeine.

Oligomeric proanthocyanidins

Oligomeric proanthocyanidins (OPCs) are potent antioxidants that can be found in red wines and grapeseed extracts. Originally discovered in the 1950s by the French scientist Jack Masquelier, OPCs may be the basis of the so-called “French Paradox” which refers to the fact that although French cooking contains more saturated fats and cholesterol producing foods, the French are 2.5 times less likely to die of coronary artery disease and its complications. Several studies have shown that red wine contains more of the OPCs than white wine and that the alcohol content is not related to the benefits.

Quercetin

Quercetin has one of the highest antioxidant effects of any flavonoid and is most widely used in the prevention and treatment of allergies and asthma. It acts by strengthening the mast cell wall and thus inhibiting the release of histamine. Quercetin also inhibits the production of cyclooxygenase and leukotrienes. These substances can cause vasoconstriction and bronchoconstriction. Quercetin does not cause the CNS depressant effects that are usually produced by prescription and OTC antihistamines. Some products also contain other flavonoids, such as hesperidin and rutin, along with quercetin; this combination may induce a synergistic affect. The pineapple stem enzyme may also be included. This aids in absorption and produces an anti-inflammatory effect.

Soy

Soy contains two widely studied isoflavonoids, daidzein and genistein. These compounds are also referred to as phytoestrogens. Phytoestrogens are 1/400 the strength of human estrogen and act as agonists and antagonists. If circulating estrogen is high, these compounds bind to receptor cells and reduce the hormone’s action. Soy also acts to stimulate the receptor site if estrogen levels are low-as, for example, during menopause-and may, therefore, help control hot flashes. These isoflavonoids may also block the production of hormone-induced cancers such breast cancer, uterine cancer, and prostate cancer. Isoflavonoids may be obtained from eating soy products or by taking supplements. Sources of soy include tofu and soybeans.

Administration

  • Bilberry: 80 to 160 mg three times a day
  • Green tea: 6 to 10 cups, or 500 mg, a day
  • OPCs: based on 2mg/kg of body weight
  • Quercetin: 500 mg four times a day
  • Soy: 50 to 100 mg of soy supplement a day.

Hazards

  • Bilberry: Because the herb may inhibit platelet aggregation, it may be unsuitable for those with a bleeding disorder. In addition, bilberry may have additive effects when used with the drug warfarin.
  • Green tea: Adverse effects include nervousness, insomnia, tachycardia, hyperacidity, GI irritation, decreased appetite, constipation, diarrhea, increased blood glucose and cholesterol levels, asthma, and allergic reactions. In addition, the caffeine in green tea may increase the stimulatory effects of ephedrine or any drug that acts as a stimulant. Administration with warfarin may lead to a decreased INR. Simultaneous use of green tea and iron supplementation reduce the absorption of iron. Green tea is contraindicated in breast-feeding patients, infants, and small children. Pregnant women should avoid or minimize use because of the caffeine. Patients with cardiovascular or renal disease, hyperthy roidism, spasms, and psychic disorders should use cautiously
  • OPCs: No adverse effects are associated with OPCs.
  • Quercetin: No adverse effects are associated with the use of quercetin. However, high doses may cause blood vessel dilation and blood thinning.
  • Soy: Adverse effects include gastrointestinal effects, such as stomach pain, loose stool, and diarrhea, asthma, and allergic reaction. In addition, soy may cause decreased absorption of calcium, iron, and zinc supplements. It may reduce the effects of estrogen, raloxifene, and tamoxifen. Patients hypersensitive to soy or soy-containing products shouldn’t use this product. High doses of soy protein may have harmful effects in women with breast cancer. Infants shouldn’t be fed soy-based formulas because of high isoflavone content. Inhalation of soy dust led to an asthma outbreak in 26 workers exposed to soy powder when unloading the product.

Clinical considerations

Since they are water-soluble compounds, flavonoid supplements may be administered with food if a patient is experiencing any type of gastrointestinal problems.

Research summary

The concepts behind the use of flavonoids and the claims made regarding their effects haven’t yet been validated scientifically.

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