Food and Behaviour Research

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9 December 2016 - Nutraingredients - The double edged sword: High doses of polyphenols may damage DNA

Nathan Gray


Many supplements and so-called 'functional foods' boast that they contain plant-derived substances known as 'polyphenols' - found naturally in fruits, vegetables, herbs and spices and numerous foods made from these. Commonly cited sources include red wine, dark chocolate, tea, coffee, and extra virgin olive oil - and their polyphenol content is often credited with some of the health benefits associated with these foods or drinks.

This new research indicates that while low doses of polyphenols (as found in most real foods) can be beneficial to various aspects of health, higher doses may actually damage health by increasing 'oxidative stress', rather than helping to reduce it. Dosage appears to be a key factor in their effects, particularly on DNA.

So unsurprisingly, real food sources of polyphenols are probably preferable to supplements.

See the associated research here:

Researchers have warned manufacturers of functional foods and supplements to keep polyphenol doses low, following conclusions that low concentrations protect but high concentrations may damage DNA. 

The review published in Nutrients looked at a wide range of human and lab-based data on the effects of polyphenols on human health – and in particular on DNA damage and oxidative stress that has been suggested to be a factor in the onset of many chronic disease states.

Led by Amaya Azqueta from the University of Navarra in Spain and Andrew Collins from the University of Oslo in Norway, the researchers reviewed publications relating to human trials, animal experiments and cell culture, grouping them according to whether polyphenols were investigated in whole foods and drinks, in plant extracts or as individual compounds.

“Results reported in the recent literature, on the whole, lend support to the hypothesis that dietary polyphenols protect the body against the effects of reactive oxygen species on DNA integrity, but do so reliably only when present at low concentrations,” said the authors.

They recommended that “greater attention be paid to the concentrations used, particularly in in vitro experiments, if the results are to be extrapolated to issues of human health”.

Indeed, the team found that while human and animal trials generally suggested polyphenols may be protective against DNA damage, some high dose animal trials and several lab-based cell culture studies that used high concentrations of polyphenols saw greater DNA damage.

“Clearly, in functional foods or phytochemical supplements, the concentration is likely to be higher than in natural foods, and experiments showing genotoxicity of phytochemicals at high doses should at least serve as a warning to designers of functional foods,” wrote Azqueta and Collins.