A new study finds a link between bacteria that cause gum disease and Alzheimer’s disease. But some researchers aren’t so sure.
Can bacteria that cause gum disease also lead to Alzheimer’s disease?
A new study suggests that it may, a discovery that could also open up a path toward a potential treatment.
But other researchers and doctors caution that it’s too early to say that this is the answer to this progressive neurodegenerative disorder.
In the study, which was published in the journal Science Advances, researchers examined the brain tissue of deceased people with Alzheimer’s disease.
In the tissue, they found Porphyromonas gingivalis, one of the main pathogens responsible for gum disease. They also detected the bacterium’s DNA in spinal fluid taken from living Alzheimer’s patients.
In addition, toxic enzymes made by the bacterium — called gingipains — showed up in many of the Alzheimer’s brain samples. Brains with more gingipains had higher amounts of proteins linked to Alzheimer’s disease, substances known as tau and ubiquitin.
Experiments in mice also suggest a connection between this bacterium and Alzheimer’s disease.
When the research team infected the gums of healthy mice with P. gingivalis, the bacterium later showed up in the brains of the animals.
Researchers also found damage to neurons and higher than normal levels of the protein beta-amyloid in the mice brain tissue.
Beta-amyloid proteins clump together to form plaques in the brains of people with Alzheimer’s disease.
Researchers were able to clear the P. gingivalis infection in the brains of mice using a molecule that binds to and blocks the gingipains. This also reduced the production of beta-amyloid and some of the neuronal damage.
The researchers suggest that this works because the bacterium relies on the enzymes for gathering nutrients and producing energy.
They said this suggests a possible treatment.
Dr. Rawan Tarawneh, a cognitive neurologist and assistant professor of neurology at The Ohio State University Wexner Medical Center, said the study findings were “interesting” and “intriguing.”
But she told Healthline the research doesn’t provide “strong enough evidence for a cause and effect relationship between P. gingivalis and Alzheimer’s disease.”
She pointed to some of the study’s limitations, such as not looking for amyloid deposits in the brains of people, the way the researchers did in mice.
Rudolph Tanzi, PhD, a professor of neurology at Harvard Medical School, cautions against overhyping the results because the study was small and still needs to be replicated by other researchers.
“I think the study is interesting,” Tanzi told Healthline, “but it is too premature to say that if you didn’t floss your teeth, you’re going to get Alzheimer’s disease. Or if you do floss your teeth, that you’re going to avoid Alzheimer’s.”
This doesn’t mean infections don’t play a role in Alzheimer’s disease.
Some researchers suspect that beta-amyloid is the brain’s way of protecting itself against these invaders.
“We’re starting to think of beta-amyloid as an antimicrobial peptide that is part of our normal immune response against infections in the brain,” said Tarawneh.
If the brain’s response is too severe, it may lead to an over-accumulation of beta-amyloid. This could cause the formation of plaques involved in Alzheimer’s disease.
Tanzi said his lab has been looking for microbes in the brains of people with Alzheimer’s disease for several years now that “may be driving amyloid deposition, as part of this antimicrobial response.”
Although their data is not published yet, they have not seen any evidence of gum disease bacteria in the brain tissue.
They have, though, detected other microbes, including viruses.
In a study published last year, Tanzi and his colleagues showed that the herpes virus can drive the production of amyloid in the brain.
“The plaques are actually trying to envelop the microbes to protect the brain,” said Tanzi.
The authors of the current study have started clinical trials to test a drug similar to the one they used in mice. This is a long way, though, from approval by the Food and Drug Administration (FDA).
These trials may give scientists a better sense of the role of P. gingivalis in the development of Alzheimer’s disease.
However, Tarawneh said “ultimately, I don’t think it will be one toxin or one infectious agent that will be the underlying cause of Alzheimer’s disease in all affected individuals.”
This is a complex disease that develops over 15 to 20 years. Many factors are involved, including age, gender, and genetic predispositions such as APOE4.
As for dental hygiene, more research is needed to determine what it means for Alzheimer’s disease.
But that doesn’t mean you shouldn’t still brush and floss your teeth regularly, and visit a dentist for annual checkups.
“Often we tend to dissociate the mouth from the rest of the body, which doesn’t make any sense,” said Dr. John Luther, the chief operating officer of Western Dental.
As with Alzheimer’s disease, though, there isn’t a clear cause-and-effect between gum disease and these other conditions.
But Luther said there’s enough of a connection that people should exercise a bit of caution.
“Individuals who are having issues with their gums should treat them” said Luther, “because all of these things point to the effects of gum disease and oral health on overall health.”