Written by Dr Victoria Sampson BDS MFDS RCS Ed Pg Dip
Did you know that similar to your gut, the mouth has its own microbiome?
Not only that, it is in fact, the second most diverse microbiome after the gut and houses approximately 700 different species of bacteria that make up 2 billion bacteria!
Unlike its relatives the gut, skin and vaginal microbiomes, the oral microbiome unfortunately has remained in the shadows, with very few even knowing they have one. What people also may not know, is how important their oral microbiome is for not only their oral health, but also their general health. When the oral microbiome is imbalanced and there are more bad bacteria than good, problems occur. In the mouth, these problems can show as tooth decay, gum disease, ulcers and bad breath to name a few. For the rest of the body, an imbalanced oral microbiome can contribute to systemic diseases such as neurological diseases, metabolic diseases, cardiovascular diseases and the list goes on.
Why is Alzheimer’s a leading cause of mortality
In the last twenty years we have witnessed an unexplainable rise in the diagnosis of neurological conditions and a decline in brain function in our population. Alzheimer’s Disease is a disease that is currently a leading cause of mortality and morbidity globally (1). It presents as one of the greatest medical challenges that we face this century due to its increasing prevalence worldwide and as yet, no effective treatment developed for it.
Furthermore, the cause of Alzheimer’s is believed to be multifactorial and a combination of genetic, environmental and lifestyle factors. Whilst some of the risk factors for Alzheimer’s cannot be altered such as our genetic makeup, the link between Alzheimer’s and oral health has gained significant traction. Not only can it be altered (and easily), but it also can be tested in a painless and easy way through saliva collection.
Inflammation: Why The Mouth is a Gateway to the Brain
One of the primary ways in which oral health affects brain function is through low grade chronic inflammation.
The oral microbiome is a delicate and beautiful balance of good and bad bacteria. If more bad bacteria are able to proliferate in the mouth, this balance can shift into what we call dysbiosis (or an imbalanced oral microbiome). Things that may cause our microbiome to shift into imbalance are things like poor oral hygiene, smoking, diet, medications we take, dry mouth and mouth breathing to name a few. Once the oral microbiome shifts into dysbiosis, this can increase our risk of local diseases such as decay and gum disease, but more importantly causes the release of inflammatory markers from the mouth to the brain.
These inflammatory markers can enter the bloodstream and cross the blood-brain barrier; a protective shield that typically prevents harmful substances from reaching the brain. Once inflammation spreads to the brain, it can contribute to the development of neurological disorders. Chronic inflammation has been linked to cognitive decline and neurodegenerative diseases such as Alzheimer’s disease, as it can damage brain cells and interfere with brain function (2).
Oral Bacteria and Brain Health
Another significant link between the mouth and the brain involves the direct effects of oral bacteria. Researchers have found that bacteria from the mouth can travel to the brain, particularly in cases of poor oral health or severe gum disease. These bacteria can enter the bloodstream through infected gums or the roots of decayed teeth, and eventually reach the brain, where they can contribute to the formation of harmful plaques.
A notable example is the bacterium Porphyromonas gingivalis, commonly found in patients with chronic gum disease. Studies have detected this bacterium in the brains of patients with Alzheimer’s disease, and it has been suggested that the bacteria’s presence may contribute to the development of amyloid plaques—a hallmark of Alzheimer’s. A 2019 study published in Science Advances (3). showed that P. gingivalis not only reaches the brain but also releases toxins known as gingipains, which can damage brain cells and accelerate cognitive decline. Another study in Taiwan performed a retrospective cohort study on 18,672 citizens and found that having gum disease for over ten years was associated with a 70% increase in the risk of developing Alzheimer’s disease (4).
If you’re still not convinced, a study published in the journal of Alzheimer’s Disease (5) further illustrated that there is a direct correlation between periodontal disease and Alzheimer’s Disease. The research looked at 6000 participants spanned over multiple age groups and followed them for up to 26 years. They performed dental examinations for gum disease as well as testing for bacteria and antibodies. The bacteria that seemed to be elevated in patients who went on to suffer Alzheimer’s disease was again, Porphyromonas gingivalis.
This discovery has sparked interest in the potential role of oral bacteria in neurodegenerative diseases. Although more research is needed to establish a definitive cause-and-effect relationship, the evidence suggests that maintaining good oral hygiene could play an important role in preventing or slowing the progression of conditions like Alzheimer’s disease. It also opens the door to saliva testing to test for bacteria such as Porphyromonas gingivalis in the microbiome and eradicating this before it can cause problems.
Stroke and Oral Health
The connection between oral health and the brain is also evident in the relationship between gum disease and stroke. Stroke occurs when blood flow to the brain is interrupted, leading to brain cell death and potentially severe neurological impairment. Gum disease is associated with an increased risk of stroke due to the systemic inflammation it causes and the potential for oral bacteria to contribute to the formation of blood clots.
A 2018 study published in the journal Stroke, (6 Sen, 2018) found that individuals with severe gum disease were at a higher risk of ischemic stroke, which occurs when a blood clot blocks an artery supplying blood to the brain. The study suggested that the chronic inflammation caused by gum disease may contribute to the formation of clots, which can travel to the brain and cause a stroke.
Moreover, researchers have found that treating gum disease can reduce markers of inflammation in the body, potentially lowering the risk of stroke. This highlights the importance of oral health not only for preventing gum disease but also for reducing the risk of serious neurological events like stroke.
The Mouth and Brain are Deeply Connected
The connection between the mouth and the brain is a reminder that the body’s systems are deeply interconnected. Poor oral health, particularly in the form of gum disease and oral infections, can have far-reaching effects on brain function and overall neurological health. Inflammation and the spread of harmful oral bacteria are two key mechanisms by which oral health can influence conditions such as Alzheimer’s disease and stroke.
As research continues to shed light on this important connection, it becomes increasingly clear that maintaining good oral hygiene is essential not only for a healthy mouth but also for a healthy brain.
For individuals looking to protect their cognitive function and reduce the risk of neurological diseases here are a few tips:
- Regular brushing
- Flossing
- Keeping up to date with dental check-ups
- All the above alongside a balanced diet and regular exercise.
If you want to learn more about the Oral Microbiome then make sure you join us for the Oral-Gut-Brain Connection Webinar with Victoria Sampson.
Find out more here.
Thank you for reading!
Food for the Brain is a non-for-profit educational and research charity that offers a free Cognitive Function Test and assesses your Dementia Risk Index to be able to advise you on how to dementia-proof your diet and lifestyle.
By completing the Cognitive Function Test you are joining our grassroots research initiative to find out what really works for preventing cognitive decline. We share our ongoing research results with you to help you make brain-friendly choices.
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- Vos T. Estimating the global mortality from Alzheimer’s disease and other dementias: A new method and results from the Global Burden of Disease study 2019. J Alzheimers Assoc. 2020.
- Kamer, A. R. (2020). Inflammation and Alzheimer’s disease: Possible role of periodontal diseases. Alzheimer’s & Dementia.
- Dominy S, et al. Porphyromonas gingivalis in Alzheimer’s disease brains: Evidence for disease causation and treatment with small-molecule inhibitors. Sci Adv. 2019.
- Chang-Kai C, et al. Association between chronic periodontitis and the risk of Alzheimer’s disease: a retrospective, population-based, matched-cohort study. Alzheimers Res Ther. 2017.
- Beydoun M, et al. Clinical and bacterial markers of periodontitis and their association with incident all-cause and Alzheimer’s disease dementia in a large national survey. J Alzheimers Dis. 2020;57–172.
- Sen E. Periodontal Disease, Regular Dental Care Use, and Incident Ischemic Stroke. Stroke. 2018.
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