Antioxidants & Polyphenols: What the Research Shows

Free Radicals and Oxidative Stress

Every cell in the body produces molecules called free radicals as a byproduct of metabolism. These are unstable molecules with an unpaired electron that can damage other cell structures. In normal amounts, they are actually useful: the immune system uses them to fight pathogens.

Problems arise when the balance between free radicals and the body’s protective mechanisms tips. This state is called oxidative stress. It has been linked to premature cell ageing, chronic inflammation and various diseases. Factors such as UV radiation, air pollution, smoking and alcohol can further increase free radical production.

What Are Polyphenols?

Polyphenols are secondary plant compounds that act as natural antioxidants. Plants produce them for protection against UV radiation, herbivores and pathogens. In the human diet, they are found in fruits, vegetables, tea, coffee, cocoa and spices.

The Main Polyphenol Classes

Class	Examples	Found in
Flavonoids	Quercetin, catechins, epicatechin	Apples, tea, cocoa, onions
Phenolic acids	Chlorogenic acid, caffeic acid	Coffee, berries, whole grains
Anthocyanins	Cyanidin, delphinidin	Aronia, blueberries, acai
Stilbenes	Resveratrol	Grapes, peanuts
Flavanols	Epicatechin, procyanidins	Cocoa, green tea

Scalbert et al. (2005) identified over 500 different polyphenols in the human diet. Typical daily intake ranges from 1 to 2 grams. That is significantly more than most vitamins.

ORAC Values: Useful but Handle with Care

The ORAC value (Oxygen Radical Absorbance Capacity) measures the antioxidant capacity of a food in the laboratory. Carlsen et al. (2010) compiled a comprehensive database of over 3,100 foods.

Some ORAC values (µmol TE/100 g):

Food	ORAC Value
Aronia (dried)	~16,000
Cocoa powder (raw)	~55,000
Blueberries	~4,600
Kale	~1,700
Apples	~3,000

Important caveat: The USDA withdrew its ORAC database in 2012. The reason: a high ORAC value in the laboratory does not automatically translate to a health benefit in the body. Bioavailability, meaning how much the body actually absorbs and utilises, varies greatly. ORAC values are a reference point, not a quality seal.

Cocoa Flavanols: The COSMOS Trial

The COSMOS trial (Cocoa Supplement and Multivitamin Outcomes Study) was one of the largest randomised controlled trials on polyphenols. Over 21,000 participants took 500 mg of cocoa flavanols or a placebo daily. The study ran for 3.6 years.

Results (Sesso et al., 2022):

• Overall cardiovascular mortality was not significantly reduced in the flavanol group.
• A subanalysis showed that participants with low fruit and vegetable intake benefited more.
• The data suggest that cocoa flavanols may positively influence certain biomarkers for heart health.

The COSMOS trial paints a nuanced picture. Cocoa flavanols are not a miracle cure, but the research points to potential benefits. Particularly for individuals whose diet contains few polyphenol-rich foods.

The Nrf2 Pathway: Activating the Body’s Own Defence

Polyphenols do not only work as direct radical scavengers. Studies suggest that they can stimulate the body’s own antioxidant production via the Nrf2 signalling pathway.

Nrf2 (Nuclear factor erythroid 2-related factor 2) is a transcription factor present in every cell. In small doses, polyphenols can trigger mild cellular stress that activates Nrf2. This then initiates the production of the body’s own protective proteins. This principle is called hormesis: a small stress stimulus strengthens the system.

This also explains why isolated antioxidants in high doses do not have the same effect as a polyphenol-rich diet.

Why Antioxidant Pills Are Not the Same as Whole Foods

Large meta-analyses show that high-dose antioxidant supplements (vitamin E, beta-carotene) provide no demonstrable benefits and can even be harmful in certain cases. A meta-analysis by Bjelakovic et al. (2007) found no benefit of antioxidant supplements for extending lifespan.

Why whole foods work better:

• Synergy effects: Hundreds of polyphenols work together. No supplement can replicate this complexity.
• Matrix effect: Fibre, fats and other components influence the absorption and effect of polyphenols.
• Dosage: Foods deliver moderate, physiological amounts. Supplements often deliver unphysiologically high doses.
• Nrf2 activation: The hormetic effect works through many small stimuli. Not through one large one.

Anthocyanins in Berries

Anthocyanins are the pigments that give berries their dark colour. Aronia, acai and blueberries are among the richest sources.

Studies suggest that anthocyanins may support vascular function. A review by Cassidy et al. (2015) found an association between higher anthocyanin intake and a reduced risk of hypertension.

Bioavailability: Anthocyanins are rapidly metabolised in the body. However, their breakdown products may also be biologically active. Research on this topic is continually evolving.

Conclusion

The evidence shows that a diet rich in polyphenol-containing foods may support the body’s own protective mechanisms. This does not mean that individual superfoods cure diseases. It means that a diverse, plant-rich diet provides the body with the tools it needs.

Isolated antioxidants in pill form cannot replace this complexity. The research clearly favours whole foods.

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Sources:

• Sesso HD et al. (2022). Effect of cocoa flavanol supplementation for prevention of cardiovascular disease events: the COSMOS randomized clinical trial. American Journal of Clinical Nutrition.
• Carlsen MH et al. (2010). The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutrition Journal.
• Scalbert A et al. (2005). Dietary Polyphenols and the Prevention of Diseases. Critical Reviews in Food Science and Nutrition.
• Bjelakovic G et al. (2007). Mortality in randomized trials of antioxidant supplements for primary and secondary prevention. JAMA.
• Cassidy A et al. (2015). Habitual intake of anthocyanins and flavanones and risk of cardiovascular disease in men. American Journal of Clinical Nutrition.