Your mouth is located very close to your brain. 

Obvious, right?

However, not many people give thought to the significance of these two organs’ proximity - in fact, it’s this very fact that makes the health of your mouth so relevant to your brain.

Today we’re going to be talking about gingipains, the oral microbiome and how taking care of your teeth and gums can help protect your brain. 

Mouth microbes

You’re probably wondering how something seemingly so unrelated as your oral health can have an impact on your brain health.

Your mouth is home to over 700 different species of bacteria. Along with all the other microbes that live rent-free in your mouth, they form what is called the oral microbiome. 

Now, these huge numbers might sound a bit grim, but don’t panic. It’s not necessary to try and blitz these microbes - similar to what we see in the gut [[link to gut-brain connection]], most of these microbes have various helpful functions and play a part in keeping your mouth healthy and suppressing the effects of “bad” bacteria and fungi.

When this happy balance is lost - a state called dysbiosis - gum disease and eventual tooth loss can develop, and inflammation starts to appear in the affected area. 

Even worse, long-term infection of disease-causing bacteria in the gums starts sending a steady drip of bacteria through your bloodstream to other parts of your body - like the brain.

This spread of bacteria and inflammation throughout the body might be connected to recent evidence suggesting that persistent oral dysbiosis could contribute to heart attacks, diabetes, and certain types of cancer.

So how do I know if my oral microbiome is imbalanced?

If harmful bacteria in your mouth start multiplying uncontrollably, this can cause a buildup of plaque, a sticky substance containing lots of bad bacteria, on your teeth.

This is a cause of gum disease, a very common condition where your gums become swollen, sore or infected. It affects between 20 to 50% of people worldwide.

One of the early signs of gum disease is bleeding gums. Your gums may bleed when you brush your teeth, and you may have bad breath. This early stage is called gingivitis.

Gum disease can progress if gingivitis is left untreated, leading to a more severe condition called periodontitis. This affects the tissues that support and hold your teeth in place. It can cause symptoms such as bleeding, painful gums, and tooth loss. Periodontitis causes body-wide, low-level chronic inflammation. It’s also been implicated in the development of a heck of a lot of inflammatory conditions.

You might be tempted to think that this doesn’t apply to you. Surely you would notice if your gums were infected?

However, many people with periodontitis experience no symptoms of infection. That’s why regular checkups with your dentist are so important. More on this later.

What does this all have to do with dementia?

Recent studies have shown a strong connection between poor oral health and an increased risk of dementia.

When you neglect your teeth and gums, harmful bacteria can build up in your mouth and they have the ability to travel to your brain - as seen in evidence from:

• Studies in live mice
• The spinal fluid of people diagnosed with probable Alzheimer’s disease
• And autopsies on human brains 

One culprit under investigation is P. gingivalis, a bacterium that we call a “keystone pathogen” in chronic gum disease.

When researchers deliberately infected the mouths of mice with this bacteria, they observed that the bacteria migrated to the mice's brains. The bacteria in the brain then appeared to increase production of amyloid-beta 1-42, a protein that forms amyloid plaques commonly seen in Alzheimer's disease. These plaques are one of the hallmarks of the disease and are believed to contribute to the brain degeneration and cognitive decline associated with Alzheimer's.

Once in the brain, these bacteria also seem to release harmful enzymes called gingipains. We know from mice and laboratory experiments that gingipains are highly toxic to brain cells. 

This loss of brain cells, for example in areas related to memory such as the hippocampus, can lead to memory loss. They also seem to prevent the immune system from turning off properly when it responds to threats, leading to chronic inflammation [[link to inflammaging article]]. 

Gingipain levels in these brains seem to correspond with the presence of abnormal proteins called tau and ubiquitin that are also associated with Alzheimer’s disease.

One way to test whether one thing causes another thing is to see what happens when you remove it. 

So researchers created special custom-made drugs to block the activity of gingipains, and found that this does indeed reduce brain inflammation, rescue neurons in the hippocampus, and prevent the production of the protein that forms amyloid plaques.

Another intriguing finding is that the cognitive abilities of people with both Alzheimer’s disease and chronic periodontitis decline six times faster than those without oral disease (although this was a small-ish study of 60 people, so further studies are needed)

And even in older people without dementia, tooth loss and gum disease appear to predict cognitive decline (!).

It’s worth noting that gingipains are also linked with other chronic inflammatory conditions like rheumatoid arthritis. This shows just how pervasive and harmful inflammation that originates in the mouth can become throughout the body.

Argh! Is gum disease reversible?

The good news is that mild cases of gum disease can usually be treated with good oral hygiene, such as brushing your teeth twice a day and flossing regularly. 

Gross fact ⚠️: If you’ve ever smelled the floss after flossing your teeth, you’ll understand how important this action is for fresh breath.

While regular brushing and flossing are crucial, they may not be enough on their own to completely eliminate plaque and tartar buildup. This is where regular dental check-ups and professional cleanings play a vital role. 

Eating a healthy diet that's low in sugar and processed foods can also help protect your teeth and gums. And, believe it or not, staying hydrated by drinking plenty of water can also help keep your mouth healthy.

More severe cases of gum disease may need additional, more intensive intervention aimed at controlling the infection and restoring gum health. 

Final word: Healthy teeth, healthy gums, healthy brain

It’s important to note that some researchers argue that the link between oral health and dementia risk may be overstated. They point out that while there are studies linking poor oral health to dementia, the evidence is not yet strong enough to definitively state that poor oral health directly causes dementia.

It’s hard to directly investigate this after all, as there’s no ethical way to induce oral disease in humans in a controlled setting to see what happens.

However, regardless of the ongoing debate, you can’t go wrong by being proactive about your oral health to maintain your overall health and well-being. 

Sometimes, we don't fully appreciate the importance of oral health until we experience dreaded toothache or notice our teeth yellowing or becoming distressed. 

It’s important to prioritise our oral health just like we would with exercise, diet, or any other aspect of our well-being.