23 March 2023

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Oral health and mental health: a possible correlation

Lara Figini

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Mental health has long been a source of confusion for researchers and clinicians, and this is largely due to a lack of understanding regarding the causal factors of neurophysiological and psychiatric disorders, which can be physiological, genetic, social and environmental.

Recent discoveries have shown that brain health is more related to systemic health than previously believed. For example, microbial communities within the body or microbiota can play a key role in noncommunicable diseases, such as obesity and diabetes, and affect mental and neurological health.

Research so far has focused predominantly on the gastrointestinal tract, which contains the majority of the microbiota associated with the human organism, both in number and diversity of species, so the primary results in the context of microbe-brain interactions have been obtained through the Gut-Brain-Axis (GBA).

GBA refers to the complex bi-directional interactions and processes used by the gut microbiome and the brain to communicate with each other.

Because bacteria possess hormone receptors and perform and utilize quorum sensing they can sense and produce autoinducing molecules that function within the bacteria in a similar way to hormones in the host by regulating bacterial growth, motility and virulence functions.

The oral cavity is the beginning of the digestive system and is the primary entry point for entry of microbes and non-microbes into the body.

The results of several literature studies demonstrate that the oral microbiota is directly involved in neuropsychiatric disorders.

Materials, methods

In a review published in Frontiers in Psychiatry in March 2022, the authors reviewed recent studies that had investigated the direct causal mechanisms by which the oral microbiota contributes to the development and progression of mental illness.

Based on these studies the authors propose a theoretical basis for an oral microbiota-brain axis (OMBA):

• microbial load and escape of metabolites,
• neuroinflammation,
• CNS signaling, and
• response to neurohormones.

Application of this OMBA framework may help link microbial dysbiosis to the progression and outcome of neuropsychiatric disorders.

This is confirmed by research presented at the American Stroke Association's 2023 International Stroke Conference. Between 2014 and 2021, researchers analyzed the potential link between oral health and brain health in approximately 40,000 adults (46% men, average age 57), without a history of stroke, enrolled in the UK Biobank.

Researchers screened participants for 105 genetic variants known to predispose people to tooth decay, edentulism and missing teeth, and the relationship between the weight of these genetic risk factors for poor oral health and brain health was assessed.

Signs of poor brain health were examined via MRI images of the participants' brains:

• white matter hyperintensity, defined as accumulated damage in the white matter of the brain, which can impair memory, balance, and mobility;
• microstructural damage, which is the degree of alteration of the fine architecture of the brain compared to images from a normal brain scan of a healthy adult of the same age.

Results

The results of this preliminary research showed that people who were genetically prone to tooth decay, were toothless, or needed dentures had a higher burden of silent cerebrovascular disease, with a 24 percent increase in the amount of white matter hyperintensity visible in MRI images.

Subjects with generally poor oral health had more damage to the fine architecture of the brain, represented by a 43% change in microstructural damage scores visible on MRI scans.

Conclusions

From the data of recent studies, researchers concluded that poor oral health can cause a decline in brain health. Dentists must talk with their patients about the importance of taking better care of their oral hygiene since it has implications far beyond the mouth. Future studies of the oral-microbiota-brain axis in conjunction with interdisciplinary approaches can be used to identify neuropsychiatric disorders risks and improve outcomes, as well as develop novel intervention and treatment strategies.