(Source: SaluGenecists, Inc.)

Flavonoids are an extensive array of phytonutrients that can be found in virtually all plant. They serve as pigments that create many of the yellows, red and oranges in our plant-based foods. Flavonoids were discovered in 1938 by a Hungarian scientist named Dr. Albert Szent-Gyorgyi who used the term vitamin P to describe them.

With over 6,000 different substances falling into the flavonoid family, the chemistry of flavonoids is complicated. Within the non-technical term flavonoids, many different chemical groups of substances can be found. These groups include flavonols, dihydroflavonols, flavones, isoflavones, flavanones, anthocyanins, and anthocyanidins. Each of these groups contains hundreds, and sometimes thousands, of different flavonoids.

Examples of some well-known flavonols include quercetin, rutin, and hesperidin while well-known flavones include apigenin and luteolin. Some flavonoids are named directly after the unique plant that contains them. For example, ginkgetin is a flavonoid from the ginkgo tree, while tangeretin is a flavonoid from the tangerine.


Physiological functions of flavonoids

  • Protect cells from oxygen damage
  • Enhance the antioxidant effect of vitamin C
  • Help protect blood vessels from rupture or leakage
  • Prevent excessive inflammation

Physiological events that can signal a need for greater flavonoid intake

  • Frequent colds or infections
  • Easy bruising
  • Excessive swelling after injury
  • Frequent nose bleeds



Functions of flavonoids

Antioxidant protection

Most flavonoids function in the human body as antioxidants, capable of neutralizing overly reactive oxygen-containing molecules and preventing them from damaging cells. In Oriental medicine, plant flavonoids have been used for centuries, honored for their antioxidant, protective properties. Examples of flavonoid-containing foods widely used in Oriental medicine include scultellaria root, cornus fruit, licorice, and green tea.

Supporting vitamin C function

The discoverer of flavonoids, Dr. Albert Szent-Gyorgyi, actually uncovered the relationship between flavonoids and vitamin C by mistake. Once when he was making a preparation of vitamin C for one of his patients with blood vessel problems, he created a preparation that was not 100% pure but that worked amazingly well. Later, when he purchased a pure solution of vitamin C, he found that it was not nearly as effective as the preparation that he had created. He proposed that it was flavonoids that were the complementary addition to the first impure preparation.

Modern day research has supported his discovery of the synergistic relationship between flavonoids and vitamin C with each substance capable of improving the antioxidant potential of the other. Additionally, many of the vitamin-related functions of vitamin C also seem to require flavonoids to be present in order for them to be effective.

Controlling inflammation

While the body uses inflammation as a natural response to danger or damage, it must always be carefully regulated in order to prevent overactivation of the immune system and unwanted immune response. Many different chemical categories of flavonoids appear to play a key role in the prevention of excessive inflammation with many type of cells involved with the immune system - including T cells, B cells, NK cells, mast cells and neutrophils being shown to alter their behavior in the presence of flavonoids.

Antibiotic and antiviral activity

In some cases, flavonoids can disrupt the function of microorganisms like bacteria and viruses. Flavonoids antiviral activity has been demonstrated in laboratory experiments with the HIV virus as well as with HSV-1, herpes simplex virus type 1.

Deficiency Factors

Causes and symptoms of flavonoid deficiency

Not only is inadequate intake of fruits and vegetables a contributing factor to flavonoid deficiency, but routine intake of highly processed fruits and vegetables can also lead to flavonoid deficiency. This is because food processing results in a tremendous loss of flavonoid content since this nutrient can be easily lost by repeated heating. Additionally, when fruits and vegetables are juiced, the pulpy fibrous flavonoid-rich parts are often removed.

Frequent colds or infections, reflective of generally weakened immune function, can be a symptom of flavonoid deficiency. Conditions that reflect increased capillary permeability such as excessive bruising, swelling after injury, nose bleeds and hemorrhoids can also be a sign of inadequate dietary intake of flavonoids.

Toxicity Factors

Causes and symptoms of flavonoid toxicity

There have been no identified toxicity symptoms for flavonoid intake. Even when supplemented at very high dosages, 140 grams per day for example, unwanted side effects do not occur. Studies examining flavonoids effects during pregnancy have failed to show problems with high-level flavonoid intake.

Cooking, Storage and Processing

Effects of cooking, storage and processing on flavonoids

The flavonoid content of food can be reduced by heat, degree of acidity (pH) and processing. Fresh cut spinach, for example, experiences a 50% reduction in total flavonoid content when boiled. While onions are a less delicate food, boiling reduces their content of the quercetin glycosides flavonoids by approximately 30%. Flavonoids are a class of nutrients particularly susceptible to loss secondary to the overcooking of food.

Drug & Nutrient Interactions

Interactions between medications and flavonoids

While the impact of medications on flavonoid status is not well researched, the effect that one flavonoid, naringin, has upon medications has been. This flavonoid, found in grapefruit juice, can increase the absorption of certain heart medications, such as nifedipine, felodipine and verapamil, as well as the antihistamine terfenadine.

Nutrient Interactions

Interactions that occur between flavonoids and other nutrients

The synergistic relationship between flavonoids and vitamin C has been well documented with each substance capable of improving the antioxidant potential of the other. It seems that many of the vitamin-related functions of vitamin C require the presence of flavonoids.

Health Conditions

Health conditions that require special emphasis on flavonoids

Individuals who have the following health conditions should pay special attention to their flavonoid status:

  • Allergy
  • Asthma
  • Atopic dermatitis
  • Candida infection
  • Cataracts
  • Diabetes
  • Gout
  • Hemorrhoids
  • Macular degeneration
  • Migraine
  • Periodontal disease
  • Stomach ulcer
  • Varicose veins


Forms in Dietary Supplements

Forms in which flavonoids are found in dietary supplements.

Citrus flavonoids, such as quercetin, rutin and herperidin are the most common forms of flavonoids found in dietary supplements. . Among these, quercetin is the most common.

Food Sources

Foods that are concentrated sources of flavonoids

Almost every single fruit, vegetable, herb and spice contain flavonoid phytonutrients. They are also found in other types of plant food, including dry beans (they give red beans, black beans and speckled beans their colors) and grains (where the flavonoids usually give foods a yellowish color). Products made from these foods (for example, wine that is made from grapes) also usually contain a wide array of flavonoids.

Since the flavonoid family is too elaborate to be able to report all of its numerous food connections, there are some especially important ones to highlight. In the fruit category, berries are the highest in the flavonoids called anthocyanidins with black raspberries, for example, oftentimes containing up to 100 milligrams per ounce. Green tea contains concentrated levels of the flavonoid components called catechins; a cup of green tea may 1,000 milligrams (or 1 gram) of these powerful antioxidant flavonoids.

While the general rule is that the more colorful the component of the food is (like the skin of the fruit) the higher the concentration of flavonoids, there is an exception to this rule. The white pulpy material that resides in the inside of citrus fruit skin and that also surrounds the citrus sections is where the fruits flavonoid concentration can be found.