Polyphenols^1,2 (also known as phenolics) are phytochemicals, natural plant chemicals with powerful antioxidant properties. There are over 8,000 identified polyphenols found in foods such as tea, wine, chocolates, fruits and vegetables. Antioxidants³ — which in addition to polyphenols include carotenoids and allyl sulfides — help protect your cells from free radical damage, thereby controlling general aging and disease potential.  

If your body does not get adequate protection, free radicals can cause cellular damage and dysfunction, raising your risk for chronic diseases such as heart disease, cancer and Alzheimer’s disease, just to name a few. Polyphenols can be broken down into four general categories — flavonoids, stilbenes, lignans and phenolic acids — with additional subgroupings^4,5 based on the number of phenol rings they contain, and on the basis of structural elements that bind these rings to one another.

As a general rule, foods contain complex mixtures of polyphenols, with higher levels found in the outer layers of the plants, such as the skin.⁶ Polyphenols give fruits, berries and vegetables their vibrant colors and contribute to the bitterness, astringency, flavor, aroma and oxidative stability of the food.

The Role of Polyphenols in Human Health

In the human body, polyphenols have diverse biological functions and properties, including:,^7,8

Fighting cancer cells9,10,11,12 and inhibiting angiogenesis13(the growth of blood vessels that feed a tumor)	Protecting your skin against ultraviolet radiation
Fighting free radicals and reducing inflammation	Promoting brain health14
Reducing the appearance of aging	Protecting against dementia and Alzheimer’s disease15,16
Modulating your gut microbiome. Polyphenols have a prebiotic effect, nourishing beneficial bacteria17,18,19,20	Improving bone metabolism, reducing your risk for osteoporosis21,22
Promoting normal blood pressure and protecting your cardiovascular system, thereby lowering your risk for cardiovascular disease.23,24 Flavonoid polyphenols help to reduce the clumping of platelets in your blood and improve the function of your cells that line your arteries and veins25	Supporting normal blood sugar levels,26 stabilizing fat metabolism and reducing insulin resistance, thereby lowering your risk for Type 2 diabetes

As noted in a 2010 scientific review in the journal Nutrients:²⁷

“Research in recent years strongly supports a role for polyphenols in the prevention of degenerative diseases, particularly cancers, cardiovascular diseases and neurodegenerative diseases … Recent studies have revealed that many of these diseases are related to oxidative stress from reactive oxygen and nitrogen species.

Phytochemicals, especially polyphenols, are the predominant contributor to the total antioxidant activities of fruits, rather than vitamin C. Polyphenols have been found to be strong antioxidants that can neutralize free radicals by donating an electron or hydrogen atom … Polyphenols … complement and add to the functions of antioxidant vitamins and enzymes as a defense against oxidative stress caused by excess reactive oxygen species (ROS).

Although most of the evidence of the antioxidant activity of polyphenols is based on in vitro studies, increasing evidence indicates they may act in ways beyond the antioxidant functions in vivo. Modulation of cell signaling pathways by polyphenols may help significantly to explain the mechanisms of the actions of polyphenol-rich diets.”

How Polyphenols Protect Your Heart Health

The research supporting polyphenols in the prevention and treatment of cardiovascular disease is particularly well-documented.²⁸ For example, higher intakes of fruit-based flavonoids (specifically anthocyanin-rich foods — fruits and berries with a blue, red or dark purple hue — and those high in flavanones, particularly citrus fruits like grapefruit, lemons and oranges) has been found to lower the risk of nonfatal myocardial infarction and ischemic stroke in men.²⁹

Keep in mind that to reap these benefits, you need to eat the whole fruit, not fruit juice, which is simply too high in fructose for optimal health. Excessive fructose is associated with insulin resistance and associated health problems, including diabetes and heart disease. Here’s a sampling of other studies showing how polyphenols helps protect your heart health:

A systematic review of 14 studies found intake of six classes of flavonoids: flavonols, anthocyanidins, proanthocyanidins, flavones, flavanones and flavan-3-ols, can significantly decrease your risk of heart disease³⁰

Researchers have long puzzled over how flavonoids help prevent heart disease, but a study³¹ published last year suggests it has to do with the fact that metabolism of flavonoids enhances their bioactivity in endothelial cells, which form the lining of your blood vessels

Flavonoids also help to reduce the clumping of platelets in your blood.³² Platelet clumping is one potential precursor in heart attacks and angina

As antioxidants, polyphenols scavenge free radicals and reduce inflammation in your body

Polyphenols also inhibit vascular endothelial growth factor (VEGF), which causes complications with atherosclerotic plaques in the arteries, a factor in cardiovascular disease33