Author: Jacob Watwood
Emerging evidence of the links between the bacteria associated with periodontal disease and cognitive impairment has been a breakthrough in the understanding and potential management of cognitive decline.[i] Increasing evidence has unlocked a greater awareness of some of the specific bacteria involved in Alzheimer’s Disease (AD), the most common form of cognitive impairment, representing 60-70% of all cases.[ii] A new study has also revealed some positive effects on brain health associated with a healthy microbiome and the availability of certain chemicals and oral bacteria.[iii]
In a healthy mouth, there are thousands of distinct microorganisms which colonise specific areas of soft as well as hard tissue. A greater understanding in recent years of these unique oral microenvironments has led to more focused therapies for improving the oral health of patients. Maintaining a diverse oral microbiome is increasingly proven to be key in supporting both oral and systemic health.[iv]
Cognitive decline – what is it, and who is most affected?
Cognitive decline is typically associated with ageing, but can affect patients at any point in their life. As well as being associated with periodontal disease, cognitive impairment is linked with hypertension, diabetes, obesity, smoking, alcohol abuse, physical inactivity, social isolation and depression.ii
Commonly known as dementia, cognitive decline affected 57 million people worldwide in 2021. Every year, there are nearly 10 million new cases reported. Dementia is currently ranked 7th in global causes of death, and is a major worldwide cause of disability.ii There are estimated to be 982,000 people in the UK living with dementia today. This figure is expected to rise to 1.4 million by 2040.[v]
Women are more likely to be affected by cognitive decline than men. Women experience a longer period of disability due to dementia, and mortality rates are higher. Women also provide the majority of care for people living with dementia.ii
How oral bacteria is connected to brain health
Although cognitive decline can be caused by a number of different factors, AD is particularly characterised by the accumulation of amyloid-β peptide within plaques in brain tissue, leading to neural cell loss, and disturbances to synaptic function.[vi] An apolipoprotein E4 (APOE4) genotype and nitric oxide (NO) deficiency are also major risk factors.iii
Pathogens linked to periodontal disease, such as Porphyromonas gingivalis, are thought to play a key role,[vii] and have been identified as a predictor of mild cognitive impairment, which is known as a precursor of AD.iii
Other bacteria, such as Fusobacterium nucleatum, a pathogen commonly found in biofilm formation of oral infections, is often present in periodontal diseaseiii and is one of the pathogens that prevents the body from producing NO.[viii] F. nucleatum links with obligate anaerobes that are associated with brain abscesses and, along with other bacteria, is implicated in the development of cognitive impairment.iii
Harmful bacteria associated with periodontal disease can enter the circulatory system via damaged oral tissue, eventually traversing the blood-brain barrier. As well as directly affecting brain health, inflammation caused by these bacteria is thought to indirectly affect brain tissue and cognitive function. Patients with AD have also been found to possess lower oral bacterial diversity compared with healthy patients.iii
In contrast, better cognitive function has been found in patients with a diverse microbiome, adequate bioavailability of NO, and higher levels of the bacteria groups Neisseria and Haemophilus.iii The presence of the bacterium Prevotella intermedia has been identified as a predictor of APOE4-carrier status. Therapies that promote oral Neisseria–Haemophilus and prevent Prevotella are thought to have potential for delaying cognitive decline.iii
Oral hygiene a must for overall health
Practising good oral hygiene, eating a healthy diet rich in vegetables to improve the bioavailability of NO, and regularly visiting the dentist for check-ups and hygiene appointments can support patients in maintaining a balanced oral microbiome.[ix]
FLEXI interdental brushes from TANDEX are a great tool to recommend to patients to help them maintain excellent oral hygiene. These ergonomically designed brushes come in 11 different sizes to suit every patient, and with the simple addition of pleasant-tasting, non-abrasive PREVENT Gel from TANDEX, patients can benefit from 900 ppm fluoride and 0.12% chlorhexidine for strengthening and antibacterial properties.
As the evidence linking periodontal health to overall health and cognitive function continues to grow, supporting patients with their oral hygiene really can help them achieve a healthier body and mind.
For more information on Tandex’s range of products,
visit https://tandex.dk/
Our products are also available from DHB Oral Healthcare https://dhb.co.uk/
[i] Asher S, Stephen R, Mäntylä P, Suominen AL, Solomon A. 2022. Periodontal health, cognitive decline, and dementia: a systematic review and meta-analysis of longitudinal studies. J Am Geriatr Soc. 70:2695–2709.
[ii] Dementia. World Health Organisation [internet]. March 2025. Available at: https://www.who.int/news-room/fact-sheets/detail/dementia. Accessed April 2025
[iii] Joanna E L’Heureux, Anne Corbett, Clive Ballard, David Vauzour, Byron Creese, Paul G Winyard, Andrew M Jones, Anni Vanhatalo, Oral microbiome and nitric oxide biomarkers in older people with mild cognitive impairment and APOE4 genotype, PNAS Nexus, Volume 4, Issue 1, January 2025, pgae543, https://doi.org/10.1093/pnasnexus/pgae543
[iv] Lamont RJ, Koo H, Hajishengallis G. The oral microbiota: dynamic communities and host interactions. Nat Rev Microbiol. 2018 Dec;16(12):745-759. doi: 10.1038/s41579-018-0089-x. PMID: 30301974; PMCID: PMC6278837.
[v] Local dementia statistics. Alzheimer’s Society. ND. Available at: https://www.alzheimers.org.uk/about-us/policy-and-influencing/local-dementia-statistics Accessed April 2025
[vi] John Hardy, Dennis J. Selkoe ,The Amyloid Hypothesis of Alzheimer’s Disease: Progress and Problems on the Road to Therapeutics.Science297,353-356(2002).DOI:10.1126/science.1072994
[vii] Beydoun MA, Beydoun HA, Hossain S, El-Hajj ZW, Weiss J, Zonderman AB. 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;75(1):157-172. doi: 10.3233/JAD-200064. PMID: 32280099; PMCID: PMC11008556.
[viii] Morou-Bermúdez E, Torres-Colón JE, Bermúdez NS, Patel RP, Joshipura KJ. Pathways Linking Oral Bacteria, Nitric Oxide Metabolism, and Health. J Dent Res. 2022 Jun;101(6):623-631. doi: 10.1177/00220345211064571. Epub 2022 Jan 26. PMID: 35081826; PMCID: PMC9124908.
[ix] University of Exeter. “Mouth bacteria may hold insight into your future brain function.” ScienceDaily. ScienceDaily, 5 February 2025. <www.sciencedaily.com/releases/2025/02/250205131556.htm>.
