The more we learn about the microbiome living in our mouths, the more we discover the surprising extent to which our oral health affects our overall health.

Introduction

How often do you really think about your mouth? Sure, you shove food into it at every meal and brush your teeth twice daily, but it might be worth giving it a little more attention.

Why? Well, here are a couple of recent studies to chew over. At the end of 2025, a study published in Neurology Open Access found that people with gum disease had a 44-per-cent-increased risk of stroke compared to those with healthy mouths.

And then a paper published at the beginning of this year found that regular flossing was associated with a lower dementia risk – the researchers found that for every 14 people who floss more than once a week, one fewer person will develop dementia.

But the link to oral health doesn’t stop at the brain. Evidence is stacking up that it can have an influence on your whole body.

GAPING WOUNDS

So what’s going on inside your mouth to cause all of this? It starts with your oral microbiome. The diverse community of microorganisms living on your teeth, gums and tongue has been linked to conditions as far-reaching as cardiovascular disease, dementia and diabetes.

According to Dr Zoe Brookes, clinical lead of the Oral Microbiome Research Group at the University of Plymouth, our mouths play host to around 700 species, inhabiting all sorts of di8erent niches. Some are beneficial, helping us to break down food, for example, while others contribute to problems like tooth erosion or bad breath.

If you brush (twice) and floss daily, you’ll be removing the bad guys regularly enough to keep them in check. But let your oral health routine slip and the nasty bacteria will soon start proliferating. This may lead to gingivitis (mild gum disease), where the gums become red, swollen and inflamed.

“In mild gum disease, there are microscopic ulcers that appear, which add up to a wound area of about 5cm2 [almost 1in2],” says Iain Chapple, professor of periodontology and consultant in restorative dentistry at the University of Birmingham.

Between 70 and 90 per cent of people have gingivitis. The good news is that it’s reversible – get your oral health routine back on track and the symptoms will soon clear up. But left untreated, it gets worse.

The problem is that some of the harmful species feed on the iron in your blood, so bleeding gums help the bacteria to flourish and the inflammation increases. You can easily find yourself stuck in a loop of inflammation and bad bacteria growth, which can become periodontitis, or severe gum disease.

Periodontitis a8ects between 45–55 per cent of the world’s population. Here, the infection causes the pocket between the gum and the tooth to deepen, sometimes by more than 7mm (0.3in). In advanced cases, it can even eat into the bone.

“With periodontitis, the total wound area is enormous. It’s the size of the palm of your hand,” says Chapple.

Think about it – that’s exposed, bleeding tissue, completely riddled with any bacteria lurking within your mouth. And now, those bacteria can hitch a ride in your blood to anywhere in your body, triggering inflammation in the organs, blood vessels, joints and tissues.

There are several species of troublesome bacteria associated with gum disease, with perhaps the worst being Porphyromonas gingivalis. It’s present in many people with healthy mouths, but is usually kept in check by the population of ‘friendly’ bacteria. It’s only when things become imbalanced that P. gingivalis begins to thrive.

According to an article published in Frontiers in Microbiology, the species is found in 85 per cent of plaque samples taken from people with advanced periodontitis. But the strange thing about P. gingivalis is that, outside of our mouths, it’s pretty pathetic.

“In the lab, if you alter its conditions even slightly, it just dies,” says Brookes. “You give it some oxygen, it dies. You put it next to another bacteria, it dies. It just likes being deep in the gum pocket, where there’s no oxygen and the [acidity] is just right.”

In its preferred conditions, P. gingivalis can proliferate – and periodontitis provides for them, allowing the bacteria to work its way into your bloodstream to cause havoc around your body.

In the last few years, there’s been an increasing amount of evidence linking P. gingivalis with atherosclerotic cardiovascular disease. This happens because the bacteria travel through blood vessels towards the heart, triggering inflammation along the way, causing the arteries to become harder, narrower and sti8er.

The good news? According to a study published in the European Heart Journal in August 2025, intensive treatment of periodontitis can slow the thickening of the carotid artery, the major vessel supplying blood to the brain, face and neck.

“This is among the most robust evidence to date that oral and cardiovascular health are interconnected,” says Prof John Deanfield, chief investigator of the trial. “Addressing periodontitis could become a powerful tool in preventing serious heart and brain events such as heart attacks and strokes.”

CIRCULAR RELATIONSHIPS

Cardiovascular disease isn’t the only condition to which P. gingivalis has been linked. Diabetes is another one. Here, the inflammation reaches the pancreas, where it can damage the beta cells that produce the hormone insulin, which is essential in reducing blood sugar levels.

But not only that, when you have any sort of infection, your immune system mobilises an attack to repel the invaders. To provide the energy for that battle, the liver releases glucose into the bloodstream and so blood sugar levels increase. Once you get better, they return to normal.

With an illness like a throat infection or flu, they’re only elevated for a few days. But gum disease can go on for a long time – months or even years – and your body will be producing insulin throughout that period to try to reduce blood sugar levels.

Eventually, the insulin receptors get tired of being constantly stimulated and stop working e8ectively. This causes insulin resistance, a precursor of diabetes, and your blood sugar levels skyrocket.

Crucially, the relationship between diabetes and gum disease is a circular one. People with diabetes have a more sugary environment in their mouths, making it easier for bacteria to thrive. And the more the bacteria thrive, the worse the diabetes gets.

Research suggests that treating gum disease in people with type 2 diabetes can o8er the same improvement in the condition as prescribing an additional diabetes medication.

Another disease that has a circular relationship is chronic kidney disease. All-cause mortality rates for people with chronic kidney disease are nine per cent higher in those who also have periodontal disease.

“We’ve actually got proof of causality there, that gum disease causes kidney disease, but also in reverse, kidney disease causes gum disease,” says Chapple.

There’s already quite a bit of data suggesting that P. gingivalis can cross the blood-brain barrier, with the bacteria being found in the brains of Alzheimer’s patients. While scientists are still trying to unpick the mechanisms behind it, it’s thought that the bacteria trigger inflammation, leading to degenerative changes that eventually cause dementia.

And more studies are coming in all the time. Evidence is similarly stacking up for gum disease being connected to pregnancy complications, rheumatoid arthritis and certain types of cancer.

EAT YOUR GREENS… AND PURPLES

If you’re feeling the need to floss and brush your teeth right now, that’s understandable – and advisable.

“Gum disease is preventable,” says Chapple. “You can stop it from happening. It’s so easily treatable. And it’s such an important risk factor for all these other health conditions.”

But if you really want to boost your chances of maintaining a healthy oral microbiome, start stocking your fridge with nitrate-rich veg such as spinach and kale.

According to Brookes, there are a few species of beneficial bacteria living on the back of the tongue that love munching on leafy green vegetables.

“They convert the nitrate in the vegetables to nitrite. You swallow the nitrite, it goes into your stomach and releases nitric oxide,” she says. Nitric oxide is a molecule that relaxes your blood vessels, which helps to reduce your blood pressure.

Beetroot also appears to have a beneficial e8ect on oral bacteria. In a small study published last year by the University of Exeter, beetroot juice shots taken twice a day were found to decrease blood pressure in older adults, and the researchers think this might be due to a shift in the oral microbiome.

“This study shows that nitrate-rich foods alter the oral microbiome in a way that could result in less inflammation, as well as a lowering of blood pressure in older people,” says co-author Prof Andy Jones.

JOINING FORCES

With more studies linking the health of the mouth and the whole body, it’s perhaps surprising that dentistry and medicine remain essentially separate disciplines.

Doctors can look in patients’ mouths for symptoms (such as signs of tonsillitis or anaemia), but they’re not trained to probe people’s gums the way a dentist would. But they’re starting to collaborate more.

“NHS England has a commissioning standard now on dental care for people with diabetes,” says Chapple. “In that, they recommend that family doctors refer people with diabetes for a gum health check and treatment. And they also recommend that oral healthcare professionals risk assess for diabetes in dental practices.”

Chapple is also involved in a study that’s aiming to detect cases of diabetes and pre-diabetes in dental practices, with a target of testing 10,000 people in the UK (3,000 tests have been carried out since April 2025).

Another pilot study run by NHS England is measuring blood pressure in dental practices. It’s a potential gamechanger, as there are a lot of people who might rarely visit their doctor, but will regularly go for a dental checkup.

So far, it’s helped to pick up significant numbers of people with undiagnosed hypertension, who are then referred on to their doctor for diagnosis.

Doctors are also driving improvements in oral healthcare for hospital patients. In 2021, Dr Graham Lloyd-Jones, a consultant radiologist at Salisbury Hospital, launched the SMILE project, which aims for all patients to have an oral health check within 24 hours of admission.

Toothbrushes and toothpaste are provided, and elderly patients are o8ered help with denture care. Lloyd-Jones now campaigns nationally to increase awareness of the importance of oral health.

“I’m determined to get this done. Doctors and nurses need to understand why it’s so important to care for a patient’s mouth while they’re in hospital,” he says.

“I liken the mouth to a bed sore, like an open wound, which is actually infecting the patient. It’s potentially infecting their blood and certainly their lungs.”

Lloyd-Jones explains that poor oral health is a major risk factor for hospital-acquired pneumonia, which is all too common and carries a high risk of death.

“Cleaning a patient’s teeth is often put in the same category as washing their body or brushing their hair,” he says. “But oral hygiene isn’t just a matter of dignity or patient comfort, it’s a matter of life and death.”

Closing

Study after study is reinforcing the link between oral and overall health, but many of us are guilty of dodging the dental floss and going years without seeing a dentist.

There might be all sorts of reasons, but it shouldn’t be because we can’t get an NHS dental appointment, are unable to a8ord private dentistry, or struggle with hygiene poverty.

Our oral health is an issue that society has to get its teeth stuck into.

Excerpt From
“Why oral hygiene is now critical to your dementia and diabetes risk”
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