For a long time, medicine treated the mouth as separate territory: the dentist looks after the teeth, the doctor looks after the rest. Biology knows no such boundary. The oral cavity is the gateway to both the digestive and the respiratory system, it hosts one of the most diverse microbial communities in the body, and inflamed gums are a wound through which bacteria and inflammatory substances enter the bloodstream. When you take good care of your mouth, you are not only protecting your smile. You are protecting your blood vessels, metabolism, blood pressure and sleep.
How to read the numbers: Fact = a finding from research or biology
have an oral disease
after periodontitis treatment
after a week of antiseptic mouthwash
The mouth as an ecosystem, not a problem to disinfect
Hundreds of species of bacteria, fungi and viruses live in the mouth. Most of them are not enemies – they help maintain balance, compete with pathogens for space, and some species even do useful work for the body. The problem is not that there are bacteria in the mouth, but that their composition shifts. Sugar, food debris between the teeth, a dry mouth and smoking favour species that form sticky plaque and trigger inflammation.
According to the World Health Organization, roughly 45% of people worldwide, around 3.5 billion, suffer from some oral disease. These are the most widespread noncommunicable diseases of all. And yet most of them do not hurt for a long time.
Periodontitis: a silent inflammation that leaves traces throughout the body
Gum inflammation starts inconspicuously – bleeding when brushing, swelling, tenderness. Left untreated, it can progress to periodontitis, in which inflammation destroys the connective tissue and bone around the teeth. Deep pockets form and teeth loosen. From the inflamed pockets, bacteria and inflammatory molecules enter the blood and affect distant organs.
Heart and blood vessels. In a joint consensus, European cardiologists and periodontologists agreed that periodontitis is associated with a higher risk of cardiovascular disease independently of other risk factors. Treating the gums reduces systemic inflammation and improves vascular function in the short term. At the same time, they acknowledge that studies showing that gum treatment reduces heart attacks or strokes are still lacking. The conclusion is therefore simple – healthy gums are a sensible part of prevention, not a substitute for treating blood pressure or cholesterol.
Blood sugar. In diabetes the relationship runs both ways: high blood sugar worsens the gums, and inflamed gums make blood sugar harder to control. A 2022 Cochrane review summarising 30 studies showed that treating periodontitis lowered glycated haemoglobin (HbA1c) by about 0.43 percentage points after three to four months.
Bleeding gums are not normal. If your gums bleed when you brush, it is a sign of inflammation, not a reason to brush less. If you have diabetes or heart disease, or during pregnancy, it is worth having your gums checked by a dentist or dental hygienist.
P. gingivalis and the brain: an intriguing lead, not a final verdict
The bacterium Porphyromonas gingivalis is one of the main drivers of periodontitis. In 2019, researchers reported finding its toxic enzymes, called gingipains, in the brains of people with Alzheimer's disease, and their levels correlated with changes in the tau protein. In mice, oral infection with this bacterium led to its spread into the brain and increased production of beta-amyloid.
It is a compelling biological story, but it is still mainly based on laboratory and animal data. In humans we cannot yet say whether the bacterium causes Alzheimer's or simply gets into a damaged brain more easily. For everyday practice, the conclusion is the same as for the heart: treating gum inflammation makes sense even while the question about the brain remains open.
Mouthwash, nitrates and blood pressure
This is one of the most fascinating things we know about the mouth. Nitrates from vegetables such as beetroot, rocket or spinach are absorbed into the blood, and the salivary glands then secrete them back into saliva. Bacteria on the tongue convert them into nitrites, from which the body produces nitric oxide – a molecule that widens blood vessels and helps maintain healthy blood pressure.
When you wipe out these bacteria, the cycle is interrupted. In a London study, healthy volunteers used a chlorhexidine antiseptic mouthwash for a week. Nitrite production in the mouth fell by 90%, blood nitrite levels by a quarter, and blood pressure rose by 2 to 3.5 mmHg. For an individual that is small, but across a whole population it is a difference that cardiology takes seriously.
This does not mean mouthwash is poison. Chlorhexidine has its place after a procedure or during acute inflammation, short term and as recommended by your dentist. The problem is daily routine "disinfection" of the mouth with strong antiseptics.
Breathing, the jaw and sleep
The mouth is not built for breathing all night. The nose filters, warms and humidifies the air, and the paranasal sinuses produce nitric oxide, which reaches the lungs with each breath. Mouth breathing dries out the mucous membranes and gums, worsens snoring and changes the environment in which the oral microbiome lives. In children who breathe through the mouth for long periods, the jaw and palate may develop differently.
Teeth and the jaw directly affect the airway. If the lower jaw is set back, the tongue falls into the throat when lying down and narrows the space for air. A faulty bite, narrow dental arches and missing back teeth are associated with snoring and sleep apnoea. Night-time teeth grinding (bruxism) wears down enamel, overloads the jaw joint and is linked to micro-awakenings. If you wake up with tense jaws or a headache, or your partner tells you that you snore, a dental examination focused on sleep may be just as important as yet another sleep tracker.
Brush gently with a soft brush for two minutes twice a day, always in the evening. Clean between your teeth once a day with interdental brushes or floss. After brushing, just spit out the toothpaste, do not rinse. Do not use antiseptic mouthwash routinely, only short term as advised by your dentist. Eat vegetables rich in nitrates. Breathe through your nose at night and, if you snore or grind your teeth, address the cause. Have a check-up and dental hygiene once or twice a year.
Hydroxyapatite, xylitol and interdental cleaning
Hydroxyapatite is the mineral that tooth enamel is made of. Toothpastes with its microcrystals help remineralise enamel. In an 18-month double-blind trial in 189 adults, hydroxyapatite toothpaste was as effective as fluoride toothpaste in preventing caries (89% versus 87% of people remained free of new decay). Fluoride has decades of data behind it and remains the standard. Hydroxyapatite, however, is a sensible alternative for those who want to avoid fluoride – if you are at high risk of caries, consult your dentist.
Xylitol has long been recommended in chewing gum and sweets because caries-causing bacteria cannot use it. A Cochrane review, however, found that the evidence for its protective effect against caries is weak and of low quality. Moreover, a 2024 Cleveland Clinic study linked higher blood levels of xylitol with a higher risk of heart attack and stroke, and showed that a xylitol-sweetened drink increases platelet reactivity. A piece of gum after a meal is a different story from tens of grams of xylitol as a sugar substitute in food – there I recommend caution.
The spaces between the teeth are places the brush cannot reach and where gum inflammation most often begins. A Cochrane review confirms that floss and interdental brushes added to toothbrushing reduce gum inflammation and plaque, although the certainty of the evidence is low. For most adults, interdental brushes of the right size are more practical than floss – a dental hygienist can determine the right size for you.
- Strong evidence Oral diseases are the most widespread noncommunicable diseases; treating periodontitis modestly improves blood sugar control in diabetes.
- Moderate evidence Periodontitis is associated with a higher risk of cardiovascular disease; antiseptic mouthwash suppresses nitrate conversion and raises blood pressure; hydroxyapatite toothpaste protects against caries comparably to fluoride.
- Weak evidence Interdental cleaning reduces gum inflammation (low certainty of evidence); the role of P. gingivalis in Alzheimer's disease in humans; the cardiovascular risk of high xylitol intake.
- No evidence That gum treatment alone prevents heart attack or dementia; that routine disinfection of the mouth brings any additional health benefit.
