Flavonoids, an amazing array of over 6,000 different substances found in virtually all plants, are responsible for many of the plant colors that dazzle us with their brilliant shades of yellow, orange, and red.
Classified as plant pigments, flavonoids were discovered in 1938 when a Hungarian scientist named Albert Szent-Gyorgyi used the term "vitamin P" to describe them.
The chemistry of flavonoids is complicated, and within the non-technical term "flavonoids" can be found many different chemical groups of substances. These groups include flavonols, dihydroflavonols, flavones, isoflavones, flavanones, anthocyanins, and anthocyanidins. Within each of these groups fall hundreds, and sometimes thousands of different flavonoids.
For example, well-known flavonols include quercetin, rutin, and hesperidin, while well-known flavones include apigenin and luteolin. Flavonoids may also be named directly after the unique plant that contains them. Ginkgetin is a flavonoid from the ginkgo tree, and tangeretin is a flavonoid from the tangerine.
How it Functions
What is are the functions of flavonoids?
Protection of cell structures
Most flavonoids function in the human body as antioxidants. In this capacity, they help neutralize overly reactive oxygen-containing molecules and prevent these overly reactive molecules from damaging parts of cells. Particularly in oriental medicine, plant flavonoids have been used for centuries in conjunction with their antioxidant, protective properties. Scultellaria root, cornus fruit, licorice, and green tea are examples of flavonoid-containing foods widely used in oriental medicine. While flavonoids may exert their cell structure protection through a variety of mechanisms, one of their potent effects may be through their ability to increase levels of glutathione, a powerful antioxidant, as suggested by various research studies.
Vitamin C support
The relationship between flavonoids and vitamin C was actually discovered by mistake. Dr. Albert Szent-Gyorgyi, the Nobel Prize winning researcher who discovered flavonoids, was attempting to make a preparation of vitamin C for one of his patients with blood vessel problems. The preparation he gave the patient was not 100% pure - it contained other substances along with the vitamin C. It worked amazingly well.
Later, when Dr. Szent-Gyorgyi purchased a pure solution of vitamin C, he found it was not nearly so effective with his patient. He suspected flavonoids as the magic addition to vitamin C in his first impure preparation. Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.
Inflammation - the body's natural response to danger or damage - must always be carefully regulated to prevent overactivation of the immune system and unwanted immune response. Many types of cells involved with the immune system - including T cells, B cells, NK cells, mast cells, and neutrophils - have been shown to alter their behavior in the presence of flavonoids. Prevention of excessive inflammation appear to be a key role played by many different chemical categories of flavonoids.
In some cases, flavonoids can act directly as antibiotics by disrupting the function of microorganisms like viruses or bacteria. The antiviral function of flavonoids has been demonstrated with the HIV virus, and also with HSV-1, a herpes simplex virus.
What are deficiency symptoms for flavonoids?
Excessive bruisability, nose bleeds, swelling after injury, and hemorrhoids can be indicators of flavonoid deficiency. Generally weakened immune function, as evidenced by frequent colds or infections, can also be a sign of inadequate dietary intake of flavonoids.
What are toxicity symptoms for flavonoids?
Even in very high amounts (for example, 140 grams per day), flavonoids do not appear to cause unwanted side effects. Even when raised to the level of 10% of total caloric intake, flavonoid supplementation has been shown non-toxic. Studies during pregnancy have also failed to show problems with high-level intake of flavonoids.
Impact of Cooking, Storage and Processing
How do cooking, storage, or processing affect flavonoids?
Heat, degree of acidity (pH), and degree of processing can have a dramatic impact on the flavonoid content of food. For example, in fresh cut spinach, boiling extracts 50% of the total flavonoid content.
With onions (a less delicate food), boiling still removes about 30% of the flavonoids (and specifically, a group of flavonoids called the quercitin glycosides). Overcooking of vegetables has particularly problematic effects on this category of nutrients.
Factors that Affect Function
What factors might contribute to a deficiency of flavonoids?
Poor intake of fruits and vegetables - or routine intake of high-processed fruits and vegetables - are common contributing factors to flavonoid deficiency. It is difficult to overemphasize the impact of processing and a non-whole foods diet on flavonoid intake. If the pulpy, fibrous parts of fruits are eliminated from the juice, and the vibrant natural colors of canned vegetables are lost during repeated heating, risk of flavonoid deficiency is greatly increased.
What medications affect flavonoids?
The impact of prescription medicines on flavonoid status is not well studied. However, in an interesting twist when looking from the other direction at the impact of flavonoids on drug status, researchers have discovered that a flavonoid in grapefruit juice called naringin can increase the absorption of certain heart-related drugs (including nifedipine, felodipine and verapamil), as well as the antihistamine terfenadine.
How do other nutrients interact with flavonoids?
Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.
What health conditions require special emphasis on flavonoids?
Flavonoids may play a role in the prevention and/or treatment of the following health conditions:
Form in Dietary Supplements
What forms of flavonoids are found in dietary supplements?
By far the most common supplemental form of flavonoids are the citrus flavonoids quercetin, rutin, and hesperidin. Of these three, the most common is quercetin.
Doses in commonly sold supplements usually range from 25-200 milligrams, although clinical studies using flavonoids often use much higher level interventions in the 500-3,000 milligram range.
It is not difficult to reach the 1,000-milligram range from dietary intake, if the diet contains an adequate amount of whole, properly prepared fruits and vegetables.
What foods provide flavonoids?
Virtually all fruits, vegetables, herbs and spices contain flavonoids. They are also found in other types of food, including dry beans (where they give red beans,black beans, and speckled beans their color) and grains (where the color provided by flavonoids is usually in the yellow family). Products made from the foods above (for example, wines made from grapes) also typically contain a wide variety of flavonoids.
While the flavonoid family is too complex to report all of its food connections, some highlights are especially important. In the fruit family, it is berries that come out highest in the chemical category of flavonoids called anthocyanins. Black raspberries, for example, may contain up to 100 milligrams of anthocyanins per ounce.
Green tea has flavonoid components called catechins that may reach 1,000 milligrams (or 1 gram) per cup. In general the more colorful components of the food - like the skins of fruits - contain the highest concentration of flavonoids. An exception to this rule, however, is the white pulpy inside of oranges. Unlike the watery orange-colored sections of this fruit, which contain virtually all of its vitamin C, the orange's flavonoids are found in the white pulpy portion inside the skin and surrounding the sections.