By Dr. Mercola
Flavonoids are a group of phytonutrients found in most fruits and vegetables. There are more than 6,000 unique flavonoids, each with its own role to play in your health.1
Flavonoids are most well known for their antioxidant and anti-inflammatory effects, but they're also useful for detoxification and have been found to lower the risk of many chronic conditions. New research even suggests they may help fight weight gain that tends to occur with age.
Flavonoids May Help You Fight 'Middle-Age Spread'
Many people gain weight as they age, but this "middle-age spread" isn't an inevitable part of aging. One simple way to minimize such weight gain is to eat more vegetables and, to some extent, fruits, and one reason why this is effective is because these foods are high in flavonoids.
A study of more than 124,000 people revealed that those with the highest intake of flavonoids had the least weight gain with age.2 Certain types of flavonoids were more effective for weight maintenance than others, particularly after the researchers accounted for fiber intake.
Anthocyanins (found in blueberries), proanthocyanidins, and total flavonoid polymers (found in tea and apples) showed the most significant effect after adjusting for fiber.
Overall, for each standard deviation above average in terms of flavonoid consumption, the study participants gained one-tenth to three-fifths of a pound less over four years. This might not sound striking, but you can consider it the icing on the cake, as it's just one of the many flavonoid benefits.
Flavonoid-Rich Foods May Lower Your Risk of Diabetes, Heart Disease and Erectile Dysfunction
Flavonoids are powerful bioactive compounds that appear to benefit numerous conditions. Research has found that women with the highest intake of flavonoid anthocyanins and flavones had the lowest levels of insulin resistance and inflammation.3
Study author Aedin Cassidy, Ph.D., of the University of East Anglia's Norwich Medical School, told Reuters:4
"We showed in population-based studies that higher habitual intakes of one class of flavonoids called anthocyanins, compounds responsible for the red/blue color of berries and other fruits and vegetables, can improve the way we handle glucose and insulin and reduce inflammation — a risk factor for heart disease and diabetes."
The study showed eating just one serving of flavonoid-rich berries daily was associated with better control of blood sugar levels and blood pressure, according to Cassidy.5
Further, research published in the British Journal of Nutrition — a systematic review of 14 studies — also found that intake of six classes of flavonoids, namely flavonols, anthocyanidins, proanthocyanidins, flavones, flavanones and flavan-3-ols, significantly decrease the risk of heart disease.6
Researchers have been puzzled about how flavonoids help to prevent heart disease, but one recent study suggests that metabolism of flavonoids increases their vascular benefits.
In particular, it appears to enhance their bioactivity in endothelial cells, which form the linings of blood vessels.7 Erectile dysfunction, which is often a signal of underlying heart disease, is also inversely associated with flavonoid intake.
A 20-year study conducted by researchers from Harvard University found men who habitually ate foods rich in flavonoids three times a week had a reduced incidence of erectile dysfunction as they aged.8
Flavonoids for Brain Power
When researchers applied apigenin to human stem cells in a petri dish, something remarkable happened — 25 days later, the stem cells had turned into neurons (an effect that didn't occur without apigenin).9
The synapses, or connections between neurons, were also "strong and more sophisticated," which is crucial for memory consolidation, learning and overall brain function.10
The researchers noted that apigenin binds to estrogen receptors, which affect the development, maturation, function, and plasticity of the nervous system. According to Stanford University, antioxidants such as flavonoids promote neurogenesis not only in a petri dish but also in rodent brains.
Flavonoids, in particular, increase neurogenesis in the hippocampus of stressed rats, possibly by increasing blood flow to the brain and/or increasing levels of brain-derived neurotrophic factor (BDNF).11 BDNF is a remarkable rejuvenator in several respects.
In your brain, BDNF not only preserves existing brain cells,12 it also activates brain stem cells to convert into new neurons and effectively makes your brain grow larger.
Separate research also found that apigenin inhibits glutamate-induced calcium signaling in cultured rat hippocampal neurons, which suggests it is a neuroprotective agent.13
The Flavonoid Apigenin May Fight Cancer
Brain health isn't the only reason to include more apigenin-rich foods in your diet; it also appears to be a potent cancer fighter. When mice implanted with cells of a particularly deadly, fast-growing human breast cancer were treated with apigenin, the cancerous growth slowed and the tumors shrank.14
Apigenin may even be one reason why drinking chamomile tea has been found to reduce thyroid cancer risk by up to 80 percent.15 Interestingly, the compound was also found to bind to 160 proteins in the human body, which suggests it has far-reaching health effects. The researchers explained:16
"… [I]n contrast to small-molecule pharmaceuticals designed for defined target specificity, dietary phytochemicals affect a large number of cellular targets with varied affinities that, combined, result in their recognized health benefits."
Even Chocolate Contains Brain-Boosting Flavonoids
Flavonoids represent up to 20 percent of the compounds present in cocoa beans, making moderate consumption of high-quality (cocoa-rich, low-sugar and organic) dark chocolate a justifiably healthy habit.
In one recent study, those who ate chocolate at least once a week had better mental performance than those who did not.17 Study author Georgie Crichton of the Sansom Institute for Health at the University of South Australia told Reuters:18
"Chocolate and cocoa flavanols have been associated with improvements in a range of health complaints dating from ancient times, and have established cardiovascular benefits, but less is known about the effects of chocolate on neurocognition and behavior."
Past research has found, however, that a flavonoid in dark chocolate called epicatechin may protect your brain after a stroke by increasing cellular signals that shield nerve cells from damage.19
Further, when diabetic patients were given a special high-flavonol cocoa drink for one month, it brought their blood vessel function from severely impaired to normal. The improvement was actually as large as has been observed with exercise and many common diabetic medications.20
Onions and Garlic: Flavonoid-Rich, Cancer-Fighting Superfoods
"Flavonoids such as quercetin can contribute to preventing damaged cells from advancing to cancer, and also have anti-inflammatory effects that may contribute to cancer prevention."
Quercetin is a powerful antioxidant with anti-inflammatory properties that may help fight chronic diseases like heart disease and cancer. In lab studies, quercetin was shown to prevent histamine release (histamines are the chemicals that cause allergic reactions.22
While apples and tea also contain quercetin, onions appear to be a particularly good source. Research from Wageningen Agricultural University in the Netherlands showed quercetin absorption from onions is double that from tea and three times that from apples.23 The flavonoid quercetin has many beneficial properties; it may:24
Reduce the risk of atherosclerosis Help prevent death from heart disease Reduce blood pressure Relieve symptoms of interstitial cystitis Reduce symptoms of prostatitis Inhibit the growth of cancer cells from breast, colon, prostate, ovarian, endometrial and lung tumors Lower lung cancer risk, especially among smokers
Flavonoid Intake Boosts Bone Health
While flavonoids' antioxidant properties have long been singled out as playing a primary role in their health benefits, researchers are looking beyond their antioxidant capacity when it comes to bone health. In fact, the compounds have been said to have "the most potential of dietary components for promotion of bone healthy beyond calcium and vitamin D."
And research suggests they have a stronger association with bone health than even general fruit and vegetable consumption.25 As noted in the Journal of Nutrition in Gerontology and Geriatrics:26
"Bioactive flavonoids are being assessed for properties beyond their chemical antioxidant capacity, including anti-inflammatory actions. Some have been reported to enhance bone formation and to inhibit bone resorption through their action on cell signaling pathways that influence osteoblast and osteoclast differentiation.
… Flavonoids as a class of phytochemicals have promise in protecting against bone loss, likely related in part to their anti-inflammatory properties."
Research published in Current Osteoporosis Reports similarly revealed that flavonoids have a favorable effect on bones.27 They referenced two human studies in women, which found positive associations between total dietary flavonoid intake and bone mineral density.
What Are the Top Sources of Flavonoids in the U.S. Diet?
Data from the U.S. Department of Agriculture (USDA) revealed the top sources of flavonoids in the U.S. diet. Researchers used data from the National Health and Nutrition Examination Survey to determine the intake of five classes of flavonoids: anthocyanidins, flavanones, flavonols, flavones, and flavan-3-ols. Top sources included:
Black tea, which provides the largest amount of flavonols (32 percent) Onions (25 percent of flavonols) Parsley, which was the largest contributor of flavones Oranges (53 percent of flavanones) Grapefruit juice (16 percent of flavanones) Brewed tea, which provides the largest amount of flavan-3-ols Blueberries, which provide the largest amount of anthocyanidins (31 percent) Bananas (21 percent of anthocyanidins) Strawberries (14 percent of anthocyanidins)
According to the study:28
"Even though bananas contain considerably less anthocyanidins than any of the berries, U.S. consumption of bananas is much higher than that of individual berries. Daily per capita intake of flavonoids in the U.S. using these data was: anthocyanidins, 5 mg; flavanones, 4 mg; flavones, 1 mg; flavonols, 10 mg; and flavan-3-ols, 112 mg."
If you're looking to get the most bang for your buck in terms of flavonoid concentration, berries, onions, parsley, tea, cocoa, and even coffee are rich sources. However, it's a good idea to consume a wide variety of flavonoids, which means consuming a variety of different healthy foods. To naturally increase the flavonoids in your diet, consider eating more of the foods listed in the chart below:29,30
Flavonols Flavan-3-ols Flavones Flavonones Anthocyanidins Onions Apples Parsley Oranges Blueberries Apples Teas (including black, green, white and oolong) Bell peppers Grapefruit Blackberries Kale Blueberries Celery Lemons Strawberries Broccoli Peaches Apples Tomatoes Cherries Garbanzo beans Pears Oranges Pears Almonds Strawberries Watermelon Cabbage Turnip greens Cocoa Chili peppers Cranberries Sweet potatoes Cantaloupe Plums Quinoa Thyme Raspberries Garbanzo beans