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expert reaction to study looking at red wine polyphenols and bacteria that stick to teeth and gums

A new study investigates the effects of polyphenols found in red wine on pathogenic bacteria that sticks to teeth and gums and cause dental plaque and cavities. The findings were published in the Journal of Agricultural and Food Chemistry.


Dr Gunter Kuhnle, Associate Professor in Nutrition and Health, University of Reading, said:

“This is a nice in vitro study using cells in a dish in the lab, but it is not possible to translate these results to what might happen in living people.  The concentration of polyphenols used appears to be considerably higher than the concentration actually found in wine (5 mg/ 100 mL compared to 0.5 mg/100 mL in wine) and the exposure was much longer than most people would keep wine in their mouths (overnight, and up to 47 hours).

“Interestingly, the two compounds which they have identified in this study (caffeic acid and p-coumaric acid), can be found in much higher amounts in other foods, especially berries.

“The press release overstates the effects of polyphenols on general health – these are not as obvious as the press release suggests.  Indeed, many polyphenols probably don’t affect disease risk at all when consumed in the amounts commonly found in the diet.  Dietary intervention studies are often only short term and rarely assess the impact on actual disease risk, and observational studies show contradicting results.

“The reference to antioxidants in the press release is also rather outdated – for more than a decade it has been well known that many polyphenols don’t act as antioxidants after they have been taken up by the body.  They are metabolised by the gut and the liver in a way that they can no longer act as an antioxidant.  The effect they have on bacteria is more likely due to their ability to bind to proteins.  The antimicrobial activity of polyphenols is well known, so this result reported here is not entirely surprising.

“The results are interesting in many ways – just not in those highlighted by the press release.  The metabolism of phenolic compounds by the bacteria in the mouth is very important and there is still a paucity of data, so more research is needed.”


Catherine Collins, Registered Dietitian, said:

“If we are what we eat, then our teeth must also reflect dietary habits.  It requires a few key players in the 700 or so mouth bacteria forming our oral microbiome to convert sugars and simple carbs to substances used by other bacteria to initiate the processes that cause tooth decay and gum disease.  So this research is interesting if only because the researchers have used extracts of drinks we’re recommended to avoid if we want to keep our teeth white – and appear to have shown a possible benefit in reducing bacterial numbers and activity, especially of the type linked to tooth decay.

“Two interesting outcomes resulted from this research.  First, soaking mouth cells for 24 hours with polyphenol extracts found naturally in red wine, grape juice, cranberry juice or coffee diminished numbers of more harmful bacteria, and also their ability to adhere to mouth cells – thus disrupting the process of making dental plaque.

“Secondly, mouth bacteria were able to ‘reshape’ some of these polyphenols into versions more easily absorbed, so improving polyphenol bioavailability and potential usefulness to us.  This confirms an influential role for mouth bacteria in helping extract the most benefit from the food we eat.  This sounds novel, but is well established in relation to the blood pressure lowering effect of nitrates which require mouth bacteria to convert dietary or medicinal nitrates into more useful nitrites that lower blood pressure.

“But unfortunately there’s no ‘lab bench to lifestyle’ recommendation today from this study.  We might now sip red wine or coffee without guilt, but none of us hold drinks in our mouth for 24 hours at a time to reproduce this particular study method.  And though the researchers showed their ‘wine extract’ polyphenols to be safe in terms of cell cultures, in real life the alcohol present alongside these red wine polyphenols not only has a bacteriocidal effect (hence the basis of alcohol mouthwashes), but is also an independent risk factor for mouth cancer.  And if you decide on cranberry juice, it’ll deliver useful polyphenols – but with sugar and fruit acids which enhance the risk of tooth decay.

“Bottom line?  Enjoy your sugar-free coffee, and even red wine – but the fact we drink them over a relatively short period of time means that for the short time they’ll spend in our mouth their influence on type of mouth bacteria will be limited.”


Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“This is interesting work done on cells outside of the body, but it is very preliminary and so one must be very cautious about extrapolating these results to any current health advice.  The findings suggest some compounds called phenols should be investigated further for their roles in preventing bacteria binding to cells and causing infection but this needs much validation.  However, the findings do not support drinking more red wine to stop people getting infections.  There is no good evidence that drinking wine per se is overall good for health – on the contrary, more and more evidence from other sources now suggests the less wine or alcohol one drinks, the lower the risks of range of disease and the lower the mortality risks.  People should not be fooled into thinking wine is good or health giving, however much they would like to hear such a message.”


* ‘Inhibition of oral pathogens adhesion to human gingival fibroblasts by wine polyphenols alone and in combination with an oral probiotic’ by Adelaida Esteban-Fernaìndez et al. published in the Journal of Agricultural and Food Chemistry on Wednesday 21 February 2018.


Declared interests

Dr Gunter Kuhnle: “I’m engaged in polyphenol research and my family owns a vineyard.”

Catherine Collins: “No conflicts of interest.”

Prof Naveed Sattar: “No COIs.”

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