What can high-flavonoid foods do for you?

  • Help protect blood vessels from rupture or leakage
  • Enhance the power of your vitamin C
  • Protect cells from oxygen damage
  • Prevent excessive inflammation throughout your body

What events can indicate a need for more high-flavonoid foods?

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

Sources of flavonoids include: apples, apricots, blueberries, pears, raspberries, strawberries, black beans, cabbage, onions, parsley, pinto beans, and tomatoes.



What are flavonoids?

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 control

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.

Antibiotic activity

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.

Deficiency Symptoms

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.

Toxicity Symptoms

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.

Drug-Nutrient Interactions

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.

Nutrient Interactions

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.

Health Conditions

What health conditions require special emphasis on flavonoids?

Flavonoids may play a role in the prevention and/or treatment of the following health conditions:
  • Allergy
  • Asthma
  • Atopic dermatitis
  • Candida infection
  • Cataracts
  • Diabetes
  • Gout
  • Hemorrhoids
  • Macular degeneration
  • Migraine
  • Periodontal disease
  • Stomach ulcer
  • Varicose veins

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.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. For more detailed information on our Nutrient Rating System, please click here.


Food Source Analysis not Available for this Nutrient

Public Health Recommendations

What are current public health recommendations for flavonoids?

At present there are no public health recommendations for flavonoids.


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This page was updated on: 2003-12-15 01:01:19
© 2002 The George Mateljan Foundation