Scientists are examining the link between bacteria in the mouth and neurodegenerative diseases such as dementia.
- New
research suggests that the bacteria living in our mouths may influence
cognitive function as we age.
- Several
bacterial species have been identified as potentially more harmful than
others, and some of these microbes may play a role in memory loss and
dementia.
- Scientists
are now exploring how oral health, along with diet and certain prebiotics,
might help slow cognitive decline and protect against conditions like
Alzheimer’s disease.
As people age, their
memory and thinking skills naturally decline. Approximately 15% of older adults
experience mild cognitive impairment, a major risk factor for dementia and
other forms of dementia such as Alzheimer’s disease.
Since cognitive decline
and dementia are growing public health concerns, scientists are working to
better understand the risk factors and find ways to reduce them. One emerging
area of research suggests that oral health may play a role in brain
health.
Now, a new study
suggests that the bacteria living in the mouth may influence cognitive function
as people age, with some harmful bacteria possibly contributing to the
development of dementia and Alzheimer’s disease.
The findings were
published in the journal PNAS
Nexus.
Diet
affects the oral microbiome
In this study,
researchers analyzed the oral microbiome of 115 individuals, including 55 with
mild cognitive impairment.
Some participants
carried the apolipoprotein E4 (APOE4) allele, which is linked to an increased
risk of cognitive decline and Alzheimer’s disease.
Within the mild
cognitive impairment group, a higher abundance of Neisseria bacteria
was associated with better executive function and visual attention.
Among healthy
individuals, Neisseria was linked to stronger working
memory.
The presence of Porphyromonas bacteria
was a key predictor of mild cognitive impairment, while Prevotella
intermedia was linked to APOE4-carrier status.
The researchers noted
that diet influences the oral microbiome, with nitrate-rich diets — such as the
Mediterranean diet and the Dietary Approaches to Stop Hypertension (DASH) diet
— supporting bacteria that are beneficial for cognitive function.
Diet
supports bacteria that are good for cognitive function
James Giordano, Ph.D., Pellegrino Center Professor, Departments of
Neurology and Biochemistry at the Georgetown University Medical Center in
Washington, DC, not involved in the study, spoke to Medical News Today.
“This study was
well-conceived and -conducted, and built upon extant research that has
fortified a link both between the gut microbiome and brain function, and the
role of the oral microbiome and health,” Giordano explained.
“This
study importantly demonstrated that maintenance of the oral microbiome can be
an important factor to the overall integrity of (oral and GI) microbiome-brain
functional reciprocity and health, and that key flora of the oral microbiome
are particularly influential in maintaining this functional integrity.”
— James Giordano, Ph.D.
“Specifically, the
authors demonstrated that the presence of particular species of oral microbiome
flora appear to be instrumental to circulatory and cerebral production of the
gaseous neuromodulating chemical nitric oxide (NO),” Giordano said.
“NO has been shown to
affect cerebrovascular tone and to regulate the intracellular signalling
processes crucial for neural functions, inclusive of those operative in
cognitive processing. NO has also been shown to exert protective effects
against neuroinflammatory processes operative in loss of neural function that
is contributory to cognitive impairment,” he continued.
Oral Bacteria, Nitric Oxide, And Neuroinflammation
“Thus,
the authors provide evidence that specific flora of the oral microbiome are
important for the production of NO and the maintenance of NO-dependent neural
functioning, which may play a role in sustaining cognitive capabilities.
[O]ther oral microbiome species appear to both inhibit normal flourishing of
beneficial flora, thereby reducing these beneficial effects, and these
pathogenic species may directly impact brain health and function by
contributing to chemical processes of neuroinflammation.”— James Giordano,
Ph.D.
Poor
oral health, gum disease may be implicated in dementia
Gum disease, or periodontitis,
has been linked to poorer cognitive function. Researchers believe this connection may be due to
the presence of harmful bacteria in the mouth, such as Porphyromonas
gingivalis, Treponema denticola, and Prevotella
intermedia.
These bacteria
contribute to gum disease by causing inflammation and damage, but they may also
affect the brain in ways that increase the risk of cognitive decline.
One way oral bacteria
may influence brain health is by entering the bloodstream when there is damage in the mouth, such as bleeding gums.
Once in the blood, these
bacteria can travel to the brain, especially in people with Alzheimer’s, as the
blood-brain barrier — the protective shield that normally keeps harmful
substances out — becomes more porous in the disease.
In fact, bacteria linked
to oral infections have been found in the brain fluid of people with brain
infections, and P. gingivalis has been detected in the
brains of Alzheimer’s patients.
Oral
bacteria may also influence inflammatory pathways
Another possible way
that oral bacteria could contribute to cognitive decline is through their
effect on the immune system.
These bacteria in the
mouth can damage its protective barrier, making it easier for harmful
substances to get into the bloodstream.
This can lead to inflammation that spreads throughout the body.
Long-term inflammation
has been connected to brain aging and memory problems, meaning these bacteria
might affect more than just oral health.
These findings
highlight the importance of maintaining good oral hygiene, not just for healthy
teeth and gums but also for long-term brain health.
How
to support the oral microbiome
Giordano pointed out
that “these findings strengthen evidence that oral health and maintenance of
key species of the oral microbiome are instrumental for brain health.”
“[T]hese findings
suggest that re-establishment or supplementation of a dominant population of
particular species of oral microflora may be beneficial to mitigating
neuroinflammation and sustaining neuro-cognitive functions,” he said.
Jennifer Bramen, PhD, senior research scientist and director of neuroimaging at the
Pacific Neuroscience Institute in Santa Monica, CA, who was also not involved
in the study, explained that incorporating nitrate-rich foods into your diet
can benefit the oral microbiome.
“This
study suggests that incorporating nitrate-rich foods like vegetables into one’s
diet can benefit the oral microbiome by promoting bacteria associated with
better oral and cognitive health outcomes while suppressing those associated
with disease.”— Jennifer Bramen, PhD
In conclusion, Giordano
added that “this study offers promise both for sampling the flora of the oral
microbiome as putative predictive biomarkers of brain health, and fortifying
the beneficial species of oral microbiome flora to maintain brain health and
function.”