Polyphenols are antioxidants.

Most people have heard that the yellow spice called turmeric is an anti-inflammatory, that capsicum pepper helps with pain and inflammation, and that cacoa found in chocolate acts as an 'anti-oxidant'.  But where do these 'ideas' come from?

The majority of studies involving the effects of polyphenols in food, on human health, are observational.  For example we observe populations where people eat a lot of apples, which contain polphenols, and notice that they have less cancer.  We then draw a conclusion of association- that eating apples reduces cancer risk.  From observations we have moved to cell and animal studies, where we know that polyphenols extracted from plants can have huge affects on gene expression, reducing inflammation and oxidative-stress.  As we are not completely like rodents such as mice, these substances are then tested on us-humans.

And these studies on humans show that concentrated polyphenols may help prevent cancer and chronic disease. but it’s not all good news as you will see.

Polyphenols are found in a variety of plants, seeds and bark. 

Polyphenols occur naturally in plants, their main function is to protect the plant against infection and stress.  There are thousands of polyphenols.  I have divided the most commonly known into Flavanoids, Phenolic acids, Tannins, Stilbenes and others to create a simplified list of some well known foods.  Some plants contain a combination of different polyphenols as you will see in the table e.g. tea, grapes, strawberries and cherries. 

You can expand the table by 'clicking' on it.

Common groups of Polyphenols

Do we absorb enough polyphenols from food and drink to improve our health?  

It is generally agreed that eating a diet high in a variety of vegetables, nuts , seeds, herbs, spices, and fruit can help prevent cancer and heart disease either by reducing oxidative stress or through changes directly in gene expression. 

This is not just based on observational studies or experiments in animals, there are small studies in humans showing that some polyphenols can have anti- cancer affects and help reduce risk factors for heart disease.  A good example is the use of 8 oz of pomegranate juice in men with prostate cancer, which results in a significant decrease in rate of cancer growth.

But not every newspaper headline for a 'super-food' is accurate. We often forget that a lot of studies have been done with high doses of polyphenols, extracted from plants, which are impossible to achieve through our diet alone; red wine being a good example as you will later read.

At present, there is no straight forward equation to calculate how much of each food makes up a 'good' dose of Polyphenols, as absorption will vary from person to person and concentration varies among plants depending on how they are farmed, stored and prepared.   Concentrations can vary dramatically in range with in the same plant- take plums for instance, their concentration of polyphenolic acid span 20mg to 120mg/100g.

There is another issue: at the moment we don't entirely understand the mechanism of action of all polyphenols, so, we cannot 'predict' side -effects or interactions with other drugs. 

Extracted polyphenols may one day become big business for pharmaceutical companies, but understanding the pathways of drug action is extremely important.  Until more research is available, eating a wide variety of foods containing polyphenols should benefit our long term health.

However, as always, go easy on your intake as an excess of flavanoids have been linked to an increased risk of leakaemia

Well known food sources of polyphenols:

  • Cacao

  • Apples, Coffee, Artichokes

  • Pomegranate, walnuts, avocadoes

  • Red wine

  • Seeds

  • Cinnamon

  • Green tea

  • Grape skins, Red grape juice

  • Turmeric, mustard

  • Onion

  • Soy

  • Capsicum

  • Oil seeds e.g Flax


Red wine- not as good as you thought?

Red wine contains Polyphenols called Stilbenes.  Stilbenes found in Japanese knot-wood, have been used for centuries in Eastern medicine to treat inflammation.  Resveratrol and its breakdown products have been shown in laboratory studies to increase lifespan and ameliorate chronic diseases associated with high fat and high calorie diets; however, the amount of Resveratrol found in a glass of red wine is just too small to produce these kinds of effects.  To reach the doses used in the mouse studies, you would require over 60 bottles of wine per day! (Baur et al., 2006)  But the results from this study, in 2006, were exciting particularly the fact that we might be able to increase the lifespan of cells.  So, the next step was to extract the Stilbenes from grapes or Knot-wood and form a concentrate that would produce this anti-oxidant and longevity affects in humans.  This is under way, but due to our lack of full knowledge on how exactly polyphenols act, predicting side -effects is difficult.  Concerns that Resveratrol stimulates oestrogen-receptors, has lead to caution in menopausal women or those with a history of breast cancer.  A recent trial using Resveratrol in patients with Multiple Myeloma, was stopped due to complications. 

The French Paradox

In the 1980's American doctors were pondering why the French, who eat high amounts of saturated fat, had paradoxically lower rates of heart disease.   The 'only' difference in diet was that the French drank a lot of red wine (there was no mention of exercise, or food portions).   And so was born the term the ' French Paradox'.   Something that is often omitted in the headlines is that the French also develop liver cirrhosis secondary to constant moderate levels of wine drinking.

Numerous studies, in rodents, using the Polyphenol, Resveratrol, have demonstrated that it can lower blood pressure by relaxing blood vessels, can be anti-bacterial or anti-fungal, reduces cancer cell development, slows memory loss, and can reduce thickening of arterial blood vessels (atherosclerosis).

In 2010 a study in which patients with colorectal cancer were given an oral Resveratrol treatment for 8 days showed slight decrease in cancer cell proliferation; however, this required doses of 0.5 g/day and 1.0 g/day which equates to 50- 100 bottles of Pinot Noir (Patel et al., 2010).

Reassuringly, at much lower doses of Resveratrol, recent human trials have shown improved 'heart health' associated with 8mg of Resveratrol, combined with a grape seed extract supplement in patients who had a heart-attack (Magyar et al. 2012).

The down side.

Despite the promising results with high and some lower doses of Resveretrol, additional research is required to understand how exactly Resveratrol acts in the body, and in turn better predict side-effects and interactions. We already know that Resveratrol has oestrogenic properties (stimulates oestrogen receptors), which could cause serious side effects, such as breast or womb cancer for women.  The other side to drinking red wine is that it contains ethanol or alcohol, which we know is detrimental to cell life.

Below is a list of wines and their stilbene content.  You will also see that grape juice may be a healthier alternative to wine, but, remember it contains lots of sugar.

  • Pinot Noir wines (9.39 mg/L)

  • Merlot (9.19 mg/L)

  • Grenache(6.37 mg/L)

  • Cabernet Sauvignon (3.23mg/L)

  • Tempranillo (3.43mg/L)

  • White juices ( 0.49 mg/L)

  • Red juices (4.73 mg/L)



Caution is recommended if considering taking resveratrol supplements and also drinking too much alcohol.

Green tea goodness

Epicstechin is the active ingredient in green tea that has been shown to reduce UV-b radiation damage to human cells, which helps protect against skin cancer.  It does this by repairing DNA that becomes damaged due to sun exposure (Sharangi, 2009). 

It is sometimes used as an adjunct to treating tendonopathies(Cook et al., 2002) such as Achilles Tendonitis (Fallon et al., 2008), and has been shown to reduce inflammation in rodents with Inflammatory Bowel Disease(Oz et al., 2013).

Most studies relating to skin cancer have been carried in mice; however, it is estimated that 5-6 cups of green tea per day can provide protection from UV-b radiation, helping reduce inflammation, immune suppression and tumour formation in skin cells.  This should be used in conjunction with sensible sun exposure i.e. avoiding hottest time of the day from 11:00 to 16:00, wearing a hat and adequate sun block if exposure time is greater than twenty minutes.

Turmeric or Curcumin

Also known as Curcumin, this yellow route vegetable looks somewhat like ginger, but thinner, and is commonly purchased in a powder form.  It is fat soluble, which means in order to ingest the active ingredients you need to eat some fat with it; a bit like the fat soluble vitamins A, D, E, and K.  Some people take Curcumin extract for osteoarthritis pains, herbal doctors prescribe it as a mild anti-inflammatory, and it is widely used in Asian and African cooking (He et al., 2015).

It comes from the Polyphenol, Ferulic acid, which is also found in mustard, giving it its yellow colour.  Curcumin is purported to have anti-cancer, anti-microbial, anti-inflammatory, anti-thrombotic, anti-cholesterol, and anti-oxidant effects, even though it is poorly absorbed from the gastro-intestinal tract (He et al., 2015). 

Because of these properties it has been trialed in patients with inflammatory bowel disease, resulting in improvements in symptoms (Suskind et al., 2013). 

One trial involving patients with early Rheumatoid arthritis, showed that 500mg of Curcumin was as good as Diclofenac at reducing pain and inflammation in joints.  There was no long term follow up to assess if this could reduce erosive disease of the joints and patients in the Curcumin group had a significantly lower CRP level to begin (CHANDRAN, B. & GOEL, A. 2012).

Studies in rats have shown regression of bowel cancer, which may be due to Curcumin having similar affects as Non-Steroidal Anti-Inflammatory Drugs (NSAIDS), such as ibuprofen.  Drugs, like ibuprofen, are known to reduce the number of adenocarcinomas (type of cancer) in the large bowel (intestine) of rats (McFadden et la 2015).  But since NSAIDS can cause stomach ulcers and problems with the kidneys, turmeric may prove to be a good alternative.

Because of its poor absorption, Curcumin is sometimes combined with Peperine, a substance found in black pepper which helps the bowel absorb more Curcumin; however, this can cause all sorts of problems with other drugs that you may be taking, as Peperine affects how the liver 'works'(Atal, C.K., et al.).


Polyphenols such as flavanoids and phenolic acids are found in lots of plants and seeds.  Eating these food types will increase your chances of remaining healthy; however, drinking more red wine is unlikely to help.  Alcohol, as we know is not good for the body.

Spices and herbs such as turmeric, pepper, cayenne, cinnamon, ginger, parsley, coriander and lemon grass improve the taste of our food and have healing properties (Raghavendra and Naidu, 2009).  Most of the headlines for 'super-foods' involve supplements containing doses not attainable through eating food, but this should not deter you from using these foods every day.

Supplements such as Resveratrol may have unknown side-effects, so, until further large scale human studies are carried out, taking Resveratrol supplements is not currently recommended (Stuart and Robb, 2013).

High doses of Flavanoids, beyond that from normal food intake, have been shown to increase the risk of Leukaemia (W. R. Bidlack & R.L Rodriguez).

Turmeric is widely prescribed by herbal doctors, for patients’ joint pains, with good effects.  It has recently been shown to have similar pain relieving effects as Diclofenac, in patients with early Rheumatoid Arthritis,  but it has not been tested against drugs that alter the immune response such as methotrexate which work extremely well to manage disease in the majority of patients.  It is sometimes combined with Peperine (black pepper extract); however, caution is advised, as Peperine is known to interact with many medications, resulting in potentially dangerous levels of other drugs and side effects.  Many people take Turmeric supplements with-out ill effect, but remember to read the ingredients.

Green tea, is a wonderful drink and can be consumed with the knowledge that it reduces your risk of skin cancer and inflammation from UV radiation.  As it contains caffeine, it may increase your symptoms of gastrointestinal acid reflux.  It can also be prepared as a tea and used when cooking instead of water or stock.


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