Hold the mouthwash

Oral bacteria is bad, right? Not all of it, finds Peta Bee.

Do you diligently tend to your gut health, consuming the kefir, live yoghurt and probiotics that help the trillions of bacteria and other microbes that reside there to flourish? If so, then it is time to turn your attention to your mouth.

Oral bacteria are best known for causing tooth decay and gum disease, but they are not all bad. Inside our mouths exists a delicate ecosystem of micro-organisms that mirrors the importance of the gut microbiome – and which researchers are discovering can be cultivated in the same way to boost health and longevity. And just as there are lifestyle habits that can upset the delicate balance of our gut flora, so it is for our oral microbiome.

Dr Raul Bescos, of the University of Plymouth’s oral microbiome research group (OMRG), says that the mouth harbours the second biggest bacterial community in the body. ‘‘For years we have been trying to kill oral bacteria because we linked it to oral disease, but we now know that up to 90 per cent of bacteria in our mouths is essential for maintaining oral and probably systemic health.’’

Last month, scientists hypothesised in a paper published in the Journal of Oral Medicine and Dental Research that sterilising mouthwashes could lower the risk of coronavirus infection, but Dr Zoe Brookes, a dentist and another member of

Plymouth’s OMRG, says that ‘‘the evidence for antiviral effects of mouthwashes is very weak’’ and we should avoid overuse of mouthwashes labelled as antibacterial – usually containing the ingredient chlorhexidine – because they can disrupt the oral microbiome.

Bescos says that, on average, we each swallow about one litre of saliva containing large quantities of micro-organisms every day. ‘‘Previously it was thought that these were killed in the acidic environment of the stomach, but new evidence has shown that a large portion of bacteria coming from the mouth can colonise the gut.’’

Emerging studies are painting a clearer picture of how our mouth microbiome helps to shape the composition of our gut microbiome, the two working synergistically to provide a defence against illness and disease. As more is discovered, so the association seems stronger. A report in the BMJ last year found the type and abundance of mouth bacteria may be linked to lung cancer risk in non-smokers, while a paper from the University of Michigan suggested that an unhealthy oral microbiome may worsen gut inflammation and inflammatory bowel disease.

In a recent study Anni Vanhatalo, professor of human physiology at the University of Exeter, discovered that one way to enhance your oral microbiome is to take a daily shot of beetroot juice, which brings about changes in mouth bacteria associated with healthier blood vessels and brain function as we age.

Beetroot is a rich source of inorganic nitrate, a compound converted by the body to nitric oxide, which has been shown in numerous studies to relax and widen blood vessels and improve blood flow, boost neurotransmission (chemical messaging in the brain) and influence how our cells use oxygen.

Our oral bacteria play a key role in turning nitrate to nitric oxide, Vanhatalo says, so for her trial, published in the journal Redox Biology, she wanted to find out if beetroot would help that process to happen. She recruited 26 healthy people aged 70 to 80 to take part in two 10-day trials. In one they were asked to drink beetroot juice and the other a placebo juice, twice a day.

Vanhatalo’s results showed that the beetroot juice drinkers, whose twice-daily shots provided about 750mg of nitrate, had higher levels of bacteria associated with good vascular and cognitive health and lower levels of bacteria linked to disease and inflammation. Systolic blood pressure dropped by an average five points (mmHg) after the beetroot juice trial, a further sign of nitrate’s effects on vascular health.

‘‘Consuming nitrate itself doesn’t have any biological effects, but it can be activated by oral bacteria and used for production of nitric oxide, which does have health benefits,’’ she says. ‘‘Human cells in bodies can’t carry out this conversion so we’re reliant on these bacteria to help us.’’

Beetroot juice isn’t the only way to boost our oral microbiome. Here are the best ways to look after your mouth’s beneficial bacteria:

1. Eat rocket, fennel and celery

Vanhatalo found pure nitrate salt to be as effective as beetroot juice, and there are plenty of other nitrate-rich vegetables, including rocket – which, weight for weight, supplies almost four times the amount of nitrate as in fresh beetroot – chard, spinach, oak leaf lettuce, fennel, celery and rhubarb.

‘‘They will all help to maintain and improve the microbiome in your mouth,’’ she says. This is particularly important as we get older. ‘‘Our body’s innate ability to produce nitric oxide via other pathways decreases when we age. We become even more reliant on dietary nitrate intake as a means for getting nitric oxide.’’

2. Keep your mouth clean

Not all bacteria in our mouth are healthy. ‘‘It seems that the balance of different species is very important and problems arise when this balance is disrupted,’’ says Dr Louise Belfield, a lecturer in biomedical science and a researcher with Plymouth’s OMRG. ‘‘It is very important that we try and control the numbers of microbes in the mouth with good oral hygiene, and mechanically removing bacteria using a toothbrush will help keep numbers in check without disrupting the balance of different species.’’

A 2020 study from Colorado State University found a correlation between daily flossing, a healthy oral microbiome and lower incidence of periodontal disease. Neglecting brushing and flossing means that potentially damaging bacteria can circulate around the body. ‘‘Bacteria from the mouth have been isolated in areas known to affect atherosclerosis and Alzheimer’s diseases,’’ Belfield says. Her advice is to brush teeth twice a day (especially before bedtime) with toothpaste that contains fluoride.

3. Avoid antibacterial mouthwashes

Bescos says that studies at Plymouth and elsewhere have shown how popular over-thecounter chlorhexidine-containing antibacterial mouthwashes – and other antibacterial products, even if they claim to be natural – can wipe out good bacteria. In one study the Plymouth team showed how just seven days of swilling with a chlorhexidine mouthwash increased levels of potentially damaging bacterial species and reduced the ability of beneficial oral bacteria to turn dietary nitrate into nitric oxide.

‘‘For years we have been trying to kill oral bacteria because we linked it to oral disease, but we now know that up to 90 per cent of bacteria in our mouths is essential for maintaining oral and probably systemic health.’’

‘‘Overuse of these products can harm the oral microbiome and compromise our health in the long term,’’ Bescos says. ‘‘We are working towards designing new oral care products using prebiotics that can be more specific to target bacteria causing oral disease while keeping alive bacteria that are needed for general good health.’’

Vanhatalo says that, although the oral microbial community bounces back fairly quickly, long-term daily use of harsh mouthwashes means your oral ecosystem never quite reaches its diverse, healthy state. She suggests tongue scraping instead.

‘‘It can be thought of as ‘gardening’ – a little bit of regular pruning and weeding that will maintain the healthy diversity of the oral ecosystem. With general mouth hygiene it can also prevent a small handful of bacteria behaving like invasive weeds and taking over the entire garden.’’

4. Eat more fibre and less sugar

‘‘A high sugar intake combined with poor oral hygiene disrupts the balance of our oral bacteria and increases acidity,’’ Vanhatalo says. She adds that food requiring a lot of chewing is beneficial for our mouth bacteria because it stimulates our salivary glands. ‘‘When saliva production is disrupted it affects the natural balance of the oral microbiome.’’ Up your fibre intake with nuts, wholegrains, pulses, carrots, broad beans, oats, bulgur wheat and dark rye crispbreads.

5. Don’t drink too much – or smoke

Researchers from the New York University School of Medicine in New York City showed that regularly drinking alcohol can promote the growth of harmful bacteria in the mouth while also preventing helpful probiotic bacteria to flourish. Their study of 1044 adults aged 55 to 87 found that certain harmful bacteria – those belonging to the species bacteroidales, actinomyces and neisseria – were more prevalent in the mouths of regular drinkers, more so when alcohol intake was high. And beneficial diseasepreventing bacterial species such as lactobacillales seemed less able to develop properly in the oral microbiomes of drinkers. Binge drinking is particularly damaging to the oral microbiome, found a study in Scientific Reports last year.

‘‘Large studies have found that alcohol caused a significant shift in the composition of the oral microbiome towards lower levels of lactobacillus, which are an important community of bacteria for our health,’’ Bescos says. ‘‘Smoking also disrupts normal saliva flow, which is important for regular influx of nitrate for oral microbes.’’

6. Try mouth-friendly prebiotics

Bescos says that there is growing evidence that prebiotic foods, those that help our good gut bugs flourish, and probiotics that provide new bacteria might also be important for our oral microbiome. ‘‘Nuts, fruits and seeds are all excellent prebiotics,’’ he says. ‘‘But also try to include live plain yoghurt, cheese, kefir, which are all natural probiotics.’’ Foods fermented with bacteria, not vinegar, are good. Foods containing inulin, such as leeks, onions, wheat, chicory root, garlic, artichokes, bananas and asparagus, along with mushrooms, might also be beneficial for the oral microbiome.