According to recent studies, the bacteria that reside in our mouths may have an impact on our cognitive abilities as we age. Researchers are now investigating the potential benefits of oral health, diet, and specific prebiotics in preventing and slowing cognitive decline and Alzheimer’s disease. 

Cognitive decline and dementia are becoming increasingly serious public health issues. About 10% to 20% of people over age 65 experience mild cognitive impairment, which is a significant risk factor for dementia and its types, including Alzheimer’s disease [1].

Researchers are constantly striving to understand risk factors and develop strategies to mitigate them. One growing area of research suggests that dental health may have an impact on brain health [2]. 

According to a recent study, oral bacteria may have an impact on cognitive function as people age, and some of these bacteria may contribute to the onset of dementia and Alzheimer’s disease.  

The journal PNAS Nexus published the findings [3].

Oral Bacteria Influence Cognitive Performance

Some Bacteria May Enhance Brain Function

Researchers examined the oral microbiomes (microorganisms living in the mouth) of 115 participants in this study. About 55 of them had mild cognitive impairment.

The researchers investigated bacteria in these samples and discovered that those with a high concentration of two types of bacteria, Neisseria and Haemophilus, perform better in brain health tests.

People with these bacteria, in particular, were better at paying attention, performing complex activities, and remembering things. These individuals also had greater levels of the ion nitrite in their mouths. 

Some Bacteria May Be Detrimental to Brain Function

However, some bacteria might be doing more harm than good. The researcher identified two bacterial groups that may be associated with poorer brain health.

The prevalence of a particular kind of bacteria called Porphyromonas, which is frequently linked to gum disease, was higher in memory-impaired individuals than in healthy individuals.

Prevotella, a second group, was associated with reduced nitrite, which may indicate poorer brain health. Additionally, these bacteria were more prevalent in individuals with the APOE4 gene, which is linked to an increased risk of Alzheimer’s. 

In short, the presence of Porphyromonas was a significant indicator of mild cognitive impairment, whereas APOE4-carrier status was associated with Prevotella intermedia.

Diet Impacts the Bacteria in the Mouth

Researchers have observed that nutrition affects the oral microbiome. Nitrate-rich meals, such as those found in the Mediterranean diet and the DASH diet, encourage the growth of bacteria that are beneficial for cognitive performance.

Nitrite is produced when bacteria break down nitrate, a naturally occurring component of a diet high in vegetables. Bacteria can also degrade nitrite to produce nitric oxide, which enhances circulation, particularly blood flow to the brain.

It suggests that consuming a lot of nitrate-rich foods may increase the number of beneficial bacteria and enhance brain function, which may be especially significant as individuals age. 

Researchers are currently investigating whether nitrate-rich beetroot juice can improve brain function in elderly individuals by affecting oral bacteria [4].

Dementia May Be Linked to Gum Disease and Poor Oral Health

There is evidence linking periodontitis, or gum disease, with reduced cognitive performance [5]. According to researchers, this connection might be due to harmful oral bacteria such as Prevotella intermedia, Treponema denticola, and Porphyromonas gingivalis.

These bacteria cause inflammation and damage to the gums, but they may also impact the brain, increasing the risk of cognitive decline [6]. 

When there is oral damage, such as bleeding gums, oral bacteria can enter the blood circulation and affect brain health. Once in the blood, these germs can reach the brain, particularly in Alzheimer’s patients, because the condition makes the blood-brain barrier, which typically keeps hazardous substances out, more permeable. 

Indeed, P. gingivalis has been discovered in the brains of Alzheimer’s patients, and bacteria associated with mouth infections have been detected in the brain fluid of those who have brain infections. 

Oral Bacteria May Affect Inflammatory Pathways

Oral bacteria may also have an impact on the immune system, leading to cognitive deterioration.

These mouth bacteria can destroy the protective barrier, allowing toxic substances to enter the blood circulation. This can result in widespread inflammation throughout the body. Chronic inflammation may lead to memory problems and brain aging, suggesting that these bacteria could impact health beyond oral hygiene.

These results emphasize the significance of keeping proper oral hygiene for healthy teeth and gums as well as for long-term brain health. 

What Do the Findings Imply?

The study’s findings demonstrate the negative impact some bacteria have on brain health changes as people age. It also raises the question of whether future dental visits could include routine tests to evaluate levels of these bacteria to detect very early indicators of deteriorating brain health.  

This study has substantial implications. Treatments to alter the balance of oral bacteria may be part of a dementia prevention strategy if some bacteria promote brain health while others cause deterioration. 

Reducing Prevotella and Porphyromonas and promoting the growth of nitrite-producing bacteria such as Neisseria may help preserve brain function as we age. Probiotics, diet modifications, dental hygiene practices, or even targeted therapies that alter the microbiome could accomplish this. 

While the researchers are still learning about the complex interactions between mouth bacteria and the brain, their findings give a solid foundation for future research.

If future research demonstrates that the oral microbiota contributes to brain health, focusing more on the bacteria in our mouths may open up new avenues for detecting and preventing dementia.

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References

• What Is Mild Cognitive Impairment? Alzheimers.gov. https://www.alzheimers.gov/alzheimers-dementias/mild-cognitive-impairment. Accessed: 2nd September, 2025. 

• Kaye, E.K., Valencia, A., Baba, N., Spiro III, A., Dietrich, T. and Garcia, R.I., 2010. Tooth loss and periodontal disease predict poor cognitive function in older men. Journal of the American Geriatrics Society, 58(4), pp.713-718.

• L’Heureux, J.E., Corbett, A., Ballard, C., Vauzour, D., Creese, B., Winyard, P.G., Jones, A.M. and Vanhatalo, A., 2025. Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype. PNAS nexus, 4(1), p.pgae543.

• L’Heureux, J. Bacteria in your mouth may hold clues to your brain health and dementia risk – new study. The Conversation. https://theconversation.com/bacteria-in-your-mouth-may-hold-clues-to-your-brain-health-and-dementia-risk-new-study-248625. Published Online: 5th February, 2025. Accessed: 2nd September, 2025.

• Wei, T., Du, Y., Hou, T., Zhai, C., Li, Y., Xiao, W. and Liu, K., 2023. Association between adverse oral conditions and cognitive impairment: A literature review. Frontiers in Public Health, 11, p.1147026.

• Ryder, M.I., 2020. Porphyromonas gingivalis and Alzheimer disease: Recent findings and potential therapies. Journal of periodontology, 91, pp.S45-S49.

• Cross, P. Some bacteria in the mouth may play a role in memory loss and dementia. Medical News Today. https://www.medicalnewstoday.com/articles/some-bacteria-mouth-microbiome-may-play-role-memory-loss-dementia. Published Online: 3rd February, 2025. Accessed: 2nd September, 2025.
• Gardner, A. Mouth bacteria may hold insight into future brain function. University of Exeter. https://news.exeter.ac.uk/uncategorized/the-bacteria-in-your-mouth-may-hold-insight-into-your-future-brain-function/. Published Online: 5th February, 2025. Accessed: 2nd September, 2025.