The Mouth–Brain Connection: How Oral Bacteria Influence Dementia Risk

We often think of the mouth and the brain as two very separate systems. One deals with chewing, speaking, and smiling; the other with memory, mood, and thought. But emerging science is showing that what happens in the mouth has profound effects on the brain, and may even influence our risk of developing dementia.

As a dentist and functional medicine practitioner, I see every day how oral health is far more than just teeth and gums. It is a window into overall health and, in particular, a key player in protecting the brain.

Why Dementia and Oral Health Are Linked

Dementia is one of the greatest health challenges of our time. In the UK, nearly one million people are living with it, and the numbers continue to rise. While age and genetics are important factors, research shows that lifestyle and health conditions play a significant role in who develops dementia, and this includes oral health¹.

Gum disease, also called periodontal disease, is a chronic infection of the gums and supporting structures of the teeth. It is caused by the build-up of harmful bacteria in the mouth. What many people don’t realise is that these bacteria don’t just stay in the mouth. They can enter the bloodstream, trigger systemic inflammation, and travel to distant organs – including the brain².

The Culprit Bacteria

One of the most studied bacteria in relation to dementia is Porphyromonas gingivalis, a key player in gum disease. Studies have found:

• P. gingivalis can travel from the mouth into the brain³.
• Once there, it produces toxic enzymes called gingipains, which damage brain cells⁴.
• Higher levels of P. gingivalis DNA have been found in the brains of people with Alzheimer’s disease compared with those without it⁵.

Other bacteria linked with gum disease, sometimes referred to as the “red complex”, also drive inflammation that may contribute to cognitive decline⁶.

How Oral Infections Affect the Brain

There are several ways oral bacteria may impact brain health:

1. Direct invasion: Bacteria and their toxins can cross the blood–brain barrier and directly damage neurons.
2. Inflammation: Chronic gum infection raises levels of inflammatory chemicals in the body, which can harm the brain over time.
3. Immune activation: The immune system remains on “high alert” due to gum disease, which can accelerate neurodegeneration.
4. Vascular effects: Gum disease increases the risk of cardiovascular problems, which are also risk factors for dementia⁷.

What the Research Says

• People with moderate to severe gum disease are more likely to experience cognitive decline⁸.
• Tooth loss, often the end result of advanced gum disease, is also linked with an increased risk of dementia⁹.
• Animal studies have shown that infection with P. gingivalis leads to hallmark changes of Alzheimer’s disease in the brain¹⁰.

Although research is ongoing, the evidence strongly suggests that protecting gum health is one way to help protect the brain.

If you’re experiencing memory loss, have periodontal disease or bleeding gums, or if you are concerned because a family member has dementia, book an Exploratory Call to find out how we can help.

References

1. Kamer AR, et al. Inflammation and Alzheimer’s disease: possible role of periodontal diseases. Alzheimer’s & Dementia. 2008.
2. Tonetti MS, Van Dyke TE. Periodontitis and atherosclerotic cardiovascular disease. J Periodontol. 2013.
3. Dominy SS, et al. Porphyromonas gingivalis in Alzheimer’s disease brains: Evidence for disease causation and treatment with small-molecule inhibitors. Sci Adv. 2019.
4. Singhrao SK, Olsen I. Assessing the role of Porphyromonas gingivalis in periodontitis to determine a causative relationship with Alzheimer’s disease. J Oral Microbiol. 2019.
5. Poole S, et al. P. gingivalis in Alzheimer’s disease brains. J Alzheimer’s Dis. 2013.
6. Socransky SS, et al. Microbial complexes in subgingival plaque. J Clin Periodontol. 1998.
7. Desvarieux M, et al. Periodontal bacteria and risk of atherosclerosis. Circulation. 2005.
8. Chen CK, et al. Periodontal disease and cognitive decline in Alzheimer’s disease. PLoS One. 2017.
9. Luo J, et al. Tooth loss and risk of cognitive decline and dementia: A meta-analysis. J Am Geriatr Soc. 2015.
10. Ilievski V, et al. Oral infection with P. gingivalis induces neuroinflammation and neurodegeneration in mice. PLoS One. 2018.