Chemicals in red wine could provide an unexpected route to healthier teeth and gums, research suggests.
In laboratory tests, the polyphenol plant compounds were found to fend off the bugs that cause tooth decay and gum disease.
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But experts warned against using the beverage as a mouth wash with unusual benefits. The chemicals in the study were used in far higher concentrations than occur naturally in wine, and for exposure times of more than 24 hours.
Nevertheless, the research is said to shed light on the roles of "good" and "bad" mouth bacteria and could point the way to new approaches to improving oral health.
The Spanish team led by Dr Victoria Moreno-Arribas, from the Institute of Food Science Research in Madrid, investigated two specific red wine polyphenols - caffeic and p-coumaric acid.
Both effectively stopped harmful bacteria such as Streptococcus mutans and Porphyromonas gingavalis sticking to human cells simulating gum tissue.
Microbial adherence to teeth and gums is a major factor in the build up of dental plaque and the development of gum disease and tooth decay.
The polyphenols were even better at combating harmful mouth bacteria when combined with a beneficial probiotic bug called Streptococcus dentisani.
Writing in the Journal of Agricultural and Food Chemistry, the scientists concluded: "Our study, based on an in-vitro (laboratory) model of bacterial adherence results, is very useful as an initial approach to go deeper into the mechanisms of action of red wine polyphenols against oral diseases."
The compounds studied are also found in coffee, grape juice and cranberry juice.
Commenting on the research, Catherine Collins, from the British Dietetic Association, said: "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.
"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 types of mouth bacteria will be limited."