NEW YORK — Seeing blood when you brush your teeth can be a warning sign of gum disease. For older adults, the warning signs of Alzheimer’s disease can be much easier to miss. However, a new study finds gum disease itself may be a sign someone is at risk for dementia. Researchers from NYU’s College of Dentistry and Weill Cornell Medicine say having more “bad” bacteria in your gums shows a connection to one of the key biomarkers for Alzheimer’s.
Their findings reveal a link between harmful gum bacteria and amyloid beta levels in a patient’s cerebrospinal fluid (CSF). Doctors say there are two main problems which occur in a patient’s brain leading to Alzheimer’s. First, amyloid beta proteins start clumping together to form plaques that interfere with signaling functions. Next, tau proteins build up in the nerve cells (neurons) and form tangles. All of this leads to brain cell death and cognitive decline in the patient.
“The mechanisms by which levels of brain amyloid accumulate and are associated with Alzheimer’s pathology are complex and only partially understood. The present study adds support to the understanding that proinflammatory diseases disrupt the clearance of amyloid from the brain, as retention of amyloid in the brain can be estimated from CSF levels,” says study senior author Mony J. de Leon, EdD, director of the Brain Health Imaging Institute at Weill Cornell Medicine in a university release. “Amyloid changes are often observed decades before tau pathology or the symptoms of Alzheimer’s disease are detected.”
So how does gum disease connect to brain health?
Researchers say there is growing evidence linking the imbalance of oral bacteria to Alzheimer’s. They key may lie in the chronic inflammation gum disease causes. Study authors say 70 percent of adults over age 65 deal with periodontal disease, which causes pockets between the teeth and gums to enlarge and harbor more bacteria.
“To our knowledge, this is the first study showing an association between the imbalanced bacterial community found under the gumline and a CSF biomarker of Alzheimer’s disease in cognitively normal older adults,” says lead author Angela Kamer, DDS, PhD, associate professor of periodontology and implant dentistry at NYU College of Dentistry. “The mouth is home to both harmful bacteria that promote inflammation and healthy, protective bacteria. We found that having evidence for brain amyloid was associated with increased harmful and decreased beneficial bacteria.”
The team examined 48 healthy seniors with no signs of dementia during this study. The group underwent oral exams so researchers could collect bacterial samples from their gumlines. Study authors also used a lumbar puncture technique to get a CSF sample of amyloid beta and tau levels.
To estimate what these protein levels looked like in the brain, researchers actually looked for lower levels of amyloid beta. Less amyloid beta in the CSF would translate to more of the protein in the brain. Researchers note higher tau levels in CSF would still equate to more brain tangles in patients.
The team then analyzed bacterial DNA from each patient’s gum samples. They looked for varieties with a known history of being harmful to oral health, such as Prevotella, Porphyromonas, and Fretibacterium. The readings also measured levels of “good” oral bacteria, including Corynebacterium, Actinomyces, and Capnocytophaga.
Could brushing more be the answer to fighting Alzheimer’s?
The results reveal patients with more harmful bacteria are more likely to have reduced levels of CSF amyloid; a warning sign the Alzheimer’s-related protein is gathering in the brain. Researchers suspect that high levels of healthy bacteria help maintain a bacterial balance and decrease inflammation. This benefit may also be protecting older adults from Alzheimer’s onset.
“Our results show the importance of the overall oral microbiome—not only of the role of ‘bad’ bacteria, but also ‘good’ bacteria—in modulating amyloid levels,” Kamer adds. “These findings suggest that multiple oral bacteria are involved in the expression of amyloid lesions.”
The study did not find any connection between gum disease and tau levels. Currently, it’s unclear if tau proteins will build up later or if some patients will avoid developing Alzheimer’s altogether. The next step in the study will involve a clinical trial to test if improving gum health through “deep cleanings” — removing deposits of plaque and tartar — changes brain amyloid levels.
The study appears in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring.