Gut health has become a wellness trend among prominent scientists in recent years for good reason.
A growing body of evidence now suggests the colony of trillions of bacteria living in our digestive systems – known as the gut microbiome – could be the key to our overall health. The more diverse those microscopic colonies are, the better our immunity to a host of diseases from cancer to heart disease and dementia.
But another area of the body is beginning to grab scientific attention for the same reason.
Experts believe the oral microbiome – a colony of more than 700 types of bacteria which live in the mouth – may be as important as the gut when it comes to the development of disease.
And if true it means that, while keeping your mouth clean is a good thing, keeping it too clean could be bad for you.
We already know that certain types of bacteria in the mouth can, if allowed to flourish, cause tooth decay and gum disease. The latest theory is they may also play a role in the development of all sorts of diseases, from mouth cancers to bowel cancer, Alzheimer’s, rheumatoid arthritis, type 2 diabetes and pneumonia.
But what research is beginning to establish is that many species of oral bacteria may actually help protect against disease.
As Dr Raul Bescos, who leads the oral microbiome research group at the University of Plymouth, explains: ‘What has most changed over the past decade is the idea we need to kill all the microbes in our mouths to protect against gum disease.
Lucy Dickinson was treated for tongue cancer when she was just 26
She has no real explanation for her tongue cancer diagnosis as she had none of the risk factors for a disease which is normally found in the over-65s
We know some of these microbes are detrimental and cause gum disease – but nearly 80 per cent of these microbes are essential for us and keep our mouth healthy, and may also be important to keep our bodies healthy.
‘By keeping this microbiome healthy we can reduce the risk of more dangerous microbes leaking into the blood and circulating around the body, where they can trigger an inflammatory response or an infection.
‘This can lead to other conditions, from heart attacks to strokes or even possibly some cancers. But we’re in the very early stages of this research and we have a lot of questions we need to better understand.’
Perhaps the most pressing area of research is the link between bacteria in the mouth and rising cancer cases in that part of the body. Over the past decade, cases in the UK have risen by more than a quarter.
More under-50s are being diagnosed than ever before, and fewer appear to have the traditional risk factors for the disease, such as heavy smoking and drinking. The human papillomavirus, HPV, a highly contagious and symptomless virus, is also a known cause of some forms of this cancer, but research suggests many younger people diagnosed aren’t carrying the infection.
One such person is Lucy Dickinson, who has had no real explanation for her tongue cancer diagnosis, at the age of just 26. The vet from Kirkby Stephen, Cumbria, who works as an adviser to a pharmaceutical company, has none of the risk factors for a disease which is normally diagnosed in the over-65s.
But in 2021 a lingering white patch on her tongue that grew and turned into ulcers was found to be cancer which had spread to a lymph node in her neck. She had surgery and six weeks of gruelling radiotherapy.
‘It was extremely painful and I went through periods of not being able to talk or eat properly,’ Lucy, now 29, says. ‘Of course, you wonder why it happened to you. In my case, I wonder if it was stress. I’m still not clear whether it could come back. We need much more research on why younger people develop this type of cancer.’
Barbara Fountain, who set up support charity Young Tongues and was diagnosed with tongue cancer aged 32 in 2019, said many younger patients ‘do not match the typical cancer patient’ and that 90 per cent of the charity’s members were HPV-negative.
Whether bacteria could be a factor is still being investigated.
Last month, actor James Van Der Beek – star of US TV show Dawson’s Creek – revealed he had been diagnosed with a form of bowel cancer aged just 47
In one recent US study which analysed the saliva samples of nearly 160,000 people, researchers linked a group of 13 types of oral bacteria to the development of head and neck cancers between ten to 15 years later.
There was also an association with Porphyromonas gingivalis – also known as P gingivalis – the main bacteria which causes gum disease. However, Dr Bescos says the research is at an early stage – and does not mean bacteria causes mouth cancer.
He says: ‘In studies like this, which show relationships between microbes and disease, we have to question whether it’s a cause of the condition or a consequence of it – did the change in the microbiome happen because of the condition, or was it the other way around?’
Another area of interest is the link between mouth bacteria and the development of bowel cancer in younger people.
Cases among under-50s have risen by about 50 per cent in the past three decades. Last month, actor James Van Der Beek – star of US TV show Dawson’s Creek – revealed he had been diagnosed with a form of bowel cancer aged just 47.
Research suggests one species of bacteria, called fusobacterium nucleatum, normally found in dental plaque, has been discovered in some bowel tumours.
How this happens is not clear – it was believed that bacteria from the mouth were killed by stomach acid. But it seems, in some cases, they might survive and enter the digestive system. If they do, the result aren’t good. Those with this type of bacteria in their bowel tumours respond less well to chemotherapy and have a shorter life expectancy. Their tumours may also be more likely to spread.
Dr Lindsay Edwards, senior lecturer in microbiology at King’s College London, says: ‘There’s some evidence that fusobacterium can be protective against cancer in the mouth – but that if it’s allowed to spread elsewhere, where it shouldn’t be, it can cause problems.’
A similar pattern is seen too in the most deadly tumour: lung cancer. Cases in the UK not linked to smoking are on the rise – accounting for about 15 per cent of the 50,000 diagnoses every year – and it is unclear why.
One study, published in the British Medical Journal, found a less-diverse mix of bacteria in the mouth was associated with a greater risk of the disease.
While the study doesn’t draw any firm conclusions, it points out that having more bacteria from the Lactobacillales species could more than double the risk of a lung cancer diagnosis, while having more Bacilli species increases the risk by 49 per cent.
Dr Lindsay Edwards, senior lecturer in microbiology at King’s College London, says: ‘There’s some evidence that fusobacterium can be protective against cancer in the mouth’
Conversely, two others – Spirochaetia and Bacteroidetes – were both linked to a reduced risk.
Oral bacteria has also been found in the gut of people with inflammatory bowel disease, ulcerative colitis and Crohn’s disease, Dr Edwards says.
Other studies have suggested high levels of bacteria that started in the mouth have been found in the hearts of nearly half of patients who develop endocarditis – a potentially fatal condition caused by inflammation of the heart valves.
In rheumatoid arthritis, studies found P gingivalis in the joints of people suffering from the inflammatory disease, and raised levels of prevotella and veillonella in the mouths of people in the early stages of the condition, and in those at risk of developing it.
Meanwhile, researchers have also found that patients with Alzheimer’s are more likely to contain build-ups of the P gingivalis bacteria.
‘What might be going on is that the body’s immune system is reacting to the presence of bacteria where it shouldn’t be,’ says Dr Bescos. ‘This causes inflammation, which in some cases can lead to changes in the way cells replicate and increases the risk of cancer.
‘But we don’t think it’s as simple as saying the type of bacteria you have in your mouth can cause a specific condition – it’s more complex than that. It’s about maintaining a balance, and about how different species of bacteria collaborate together.’
So what can anyone do to foster a good balance of bacteria in their mouth?
Experts say all research suggests that avoiding oral diseases linked to poor dental health lowers the risk of these problems.
Dr Bescos says: ‘In many of these scenarios, oral health is significantly impaired. The hypothesis is that damage to the gums allows bacteria to leak from the mouth to the bloodstream, and spread throughout the body.’
Experts recommend that anyone with signs of gum disease seek treatment. The condition, also known as gingivitis, is where the gums become red, swollen and sore, and often bleed. It’s usually caused by a build-up of plaque in the teeth. This is typically removed during teeth-cleaning, but poor technique, not using floss, using an old toothbrush or infrequent brushing can increase gum disease risk.
A dentist should be able to diagnose the condition and provide treatment. This may include deep cleaning of the teeth and gums, antibiotics, gum surgery or even tooth removal.
And while the link between mouth bacteria and deadly diseases is still under investigation, some data is clear. Studies show treating gum disease improves artery function around the heart and reduces overall inflammation in the body.
‘If you can treat gum disease you potentially protect the body against a whole other range of problems,’ says Dr Edwards. ‘If people brush their teeth twice a day and look after their oral microbiome, it really could help in stopping lots of systemic inflammatory diseases.’
How clean is too clean, though? Studies have found that using some types of mouthwash can increase blood pressure, cause type 2 diabetes and may even be linked to cancer.
It’s been suggested that is because it destroys ‘good’ bacteria in the mouth which might allow other types of ‘bad’ bacteria to proliferate.
One study, which made headlines earlier this year, found daily use of Listerine’s Cool Mint mouthwash increased the amount of Fusobacterium and Streptococcus anginosus – the bacteria have been linked to colon and gastric cancers if they move from the mouth.
But it’s important to note that no cases of cancer were identified in the study, nor is there any good evidence that mouthwash is linked to cancer.
Dr Bescos advises avoiding using mouthwash which is advertised as antibacterial, as this could potentially remove ‘good’ bacteria.
And until we have better evidence on how to maintain the ideal oral microbiome, alongside brushing and flossing, cut down on alcohol and don’t smoke.
And if your mouth is healthy, you might also be helping your gut. Dr Bescos adds: ‘There’s emerging evidence suggesting the oral microbiome can significantly influence the gut microbiome, so a healthy mouth may mean a healthy gut.’
