Polyphenols: health benefits, dietary sources and bioavailability

In the past 30 or so years researchers and food manufacturers have become increasingly interested in a certain type of antioxidant, known as polyphenols, and the role that they play in the body. The main reason for this interest stems from the antioxidant properties of polyphenols, their great abundance in our diet, and their probable role, backed up by much research, in the prevention of various diseases associated with oxidative stress, such as cancer and cardiovascular and neuro-degenerative diseases.

What are Polyphenols?

Polyphenols are phytochemicals, meaning compounds found abundantly in natural plant food sources, that have antioxidant properties. Based on their chemical structure, they are classified as flavonoids or non-flavonoids. Flavonoids form the largest group of over 9000 compounds. They are found in foods such as tea, wine, chocolates, fruits, vegetables, and extra virgin olive oil.

Polyphenols are now widely considered to play an important role in maintaining health and well-being throughout the body, mainly as a result of their antioxidant activity. Antioxidants as a group help protect the cells in the body from free radical damage, thereby controlling the rate at which we age.

During energy production in the mitochondria some oxygen molecules are converted to dangerous free radicals called reactive oxidative species (ROS). Cells are equipped with ROS eliminating antioxidant enzymes to neutralise any ROS. But if free radical production exceeds the cell’s natural production of antioxidants, ROS can cause oxidative damage to the vital components of our cells, which include proteins, lipids (fats) and DNA.

Overproduction of free radicals can also lead to activation of pro-inflammatory transcription factors (eg Nuclear Factor kappa-B) and increase inflammatory cytokines. Oxidative damage and inflammation are key factors in the development of various degenerative diseases such as heart disease, cancer, Alzheimer’s disease and autoimmune diseases. On the other hand, a certain level of free radicals is useful in the body, for example playing a role in the immune system.

Antioxidant properties – what are antioxidants?

An antioxidant is a chemical that helps to protect against cell damage by counteracting the destructive action of highly reactive free radical molecules.

Our bodies do produce antioxidants, for example substances such as glutathione and coenzyme Q10 are important antioxidants. However, a good dietary intake is also important.

The body’s natural production of antioxidants declines as we age so it becomes even more important to source them from your diet. Antioxidants are considered to be one of the most important aspects of nutrition for overall well-being.

Benefits of Polyphenols

Research has shown polyphenols are beneficial in a number of chronic diseases, for example:

Brain Health: Research attests to the fact that polyphenols may actually help to lower the risk of neuro-degenerative diseases such as Alzheimer’s disease, due to their role in combating oxidative stress.

Cardiovascular health: Polyphenols that are found in cocoa have been shown play a role in reducing cardiovascular stress through the inhibition of LDL cholesterol oxidation. These compounds also increase the vasodilation of blood vessels to promote circulation. It is important to bear in mind that organic dark chocolate, 72% cacao and above, is where the benefits have been found – so check this on the label before purchasing for this purpose.

Type 2 Diabetes: Polyphenols have been found to play a role in lowering inflammation in the body, reducing insulin resistance and also stabilising blood sugar and fat metabolism.

Cancer: Multiple studies have demonstrated the activity of polyphenols in the prevention of cancer. The researchers believe that the antioxidant behaviour of polyphenols help to protect DNA from free radical damage, which can trigger the development of cancer. Polyphenols also reverse the markers in DNA that are considered to increase tumour growth.

Osteoporosis: This is a condition characterised by the structural deterioration of bone tissue which in turn leads to an increase in bone fragility and increased susceptibility to bone fractures. Research suggest that Polyphenols, once again due to their antioxidant activity, have a beneficial effect on bone metabolism and reduce the risk of developing osteoporosis.

Arthritis: Research is also now suggesting that polyphenols have a beneficial effect on arthritis, as highlighted in an article on Nutraingredients:

“A compound found in green tea, may prove effective in treating rheumatoid arthritis, as its anti-inflammatory action is expressed without blocking other critical cellular functions, US researchers have shown.

The phytochemical, epigallocatechin-3-gallate (EGCG), may well form a natural alternative to current drugs used to treat rheumatoid arthritis. These therapies are expensive, immunosuppressive and sometimes unsuitable for long-term use.”

This compound (EGCG) is one of the four primary polyphenols found in fresh tea leaves.

Types of Polyphenols

Polyphenols are divided into four categories and are found in a variety of different foods:

Flavonoids

These are the most well-known and largest group of polyphenols, eg quercetin. They are divided into a number of subgroups according to their structural differences (flavones, dihydroflavonols, flavonols, flavan-3-ols, flavanols, anthocyanidins, isoflavones and proanthocyanidins). They are generally found in low concentrations and the richest sources are onions, broccoli, blueberries, kale, red wine and tea.

Stilbenes

These are found only in very low quantities in the human diet. They include resveratrol, which is considered to have anti-carcinogenic effects. However, this is only found in very low quantities in red wine and grapes so any beneficial effect at this level is minimal.

 Lignans

The richest dietary source of lignans is linseeds and other cereals, grains, fruits and certain vegetables.

 Phenolic Acids

There are two distinct classes of phenolic acids: derivatives of benzoic acid and derivatives of cinnamic acid of which tea, certain red fruits, black radish and onions are sources. However, again only at very low levels.

The Best Sources of Polyphenols

Flavonoids are the most well-known polyphenol group that, as mentioned above, are found in red wine, dark chocolate, green tea and various fruits and vegetables.

To benefit from polyphenol consumption it is essential to eat a wide variety of foods that are rich in them; namely fruits, vegetables and seeds, which are well recorded as being among the richest sources.

Choosing foods on a daily basis that represent a full range of colours – green, purple, red, orange and yellow – and aiming for half a plate of vegetables at both lunch and supper.

Bioavailability, absorption and metabolism

However, as is the issue with many nutrients, there is the problem of bioavailability – how well your body can absorb the nutrients contained in the food. In the case of polyphenols the body recognises them as xenobiotics (ie a foreign substance) and their bioavailability is fairly low in comparison to micro and macro-nutrients.

Indeed, as research suggests: “The polyphenols that are the most common in the human diet are not necessarily the most active within the body, either because they have a lower intrinsic activity or because they are poorly absorbed from the intestine, highly metabolized, or rapidly eliminated.”

As polyphenols are fat soluble, absorption can be increased by eating polyphenol rich foods alongside healthy fats (ie avocado, nuts, seeds, olive oil, oily fish – most of these foods also contain polyphenols!). Some are best cooked, for example, the absorption of beta-carotene in carrots and lycopene in tomatoes is improved with cooking.

Only a small proportion of polyphenols are absorbed in the small intestine (estimated to be about 5-10%), others reach the large intestine almost unchanged. The remaining 90-95% may accumulate in the large intestinal lumen where they are subjected to the enzymatic activity of the gut microbial community.  The colonic microbiota play an important role in breaking down the original polyphenolic structures into a series of low molecular weight phenolic metabolites which are then absorbed.

Polyphenols and the Gut Microbiome

As discussed above the gut bacteria have an important role in modulating the bioavailability of polyphenols. The relation of the gut microbiota is two-way and polyphenols have a prebiotic effect increasing the number of beneficial bacteria in the gut. Much of the research into this area has so far been conducted on green tea which has been shown to increase good bacteria in the gut and reduce undesirable bacteria.

Around 100 trillion bacteria make up the microbiome in the gut and it has become very clear that the health of your microbiome is absolutely critical to overall health; both mental and physical.

Cytoplan products

Eye-Cyt

Eye Cyt is a high potency antioxidant formula, containing a comprehensive range of nutrients relevant for eye health. The formula contains a powerful mix of carotenoids and flavonoids comprising natural vitamin E, lutein (providing Zeaxanthin), bilberry extract and grape seed extract (providing polyphenols).

Phytoshield

Phytoshield is a very potent and powerful phyto-antioxidant nutrient formula, containing high levels of flavonoids and carotenoids, as well as green tea extract (95% polyphenols)

Phyte-Inflam

A natural phyto-nutrient and herbal complex containing curcumin from turmeric, gingerols from ginger root and piperine from pepper.

Phyto-Flavone

A source of natural isoflavones providing daidzein, glycitein and genistein.

Honey Bee Propolis

A sticky resin gathered by bees from leaf buds, the bark of trees and other botanical sources. Propolis is used by bees for its natural antibiotic, anti-fungal and antibacterial properties. Propolis contains 180 natural compounds including flavonoids and phenolics which account for much of its biologic activity.


If you have any questions regarding the health topics raised in this article then please do get in touch via phone (01684 310099) or e-mail ([email protected])

Amanda Williams & The Cytoplan Editorial Team: Joseph Forsyth, Clare Daley and Simon Holdcroft


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