Study Shows Bacterial Imbalance Linked to Development of Alzheimer Disease

Alzheimer disease, a common and particularly cruel type of dementia, gradually robs its victims of memory and, ultimately, their sense of self. Although it is not a normal part of aging, it affects more than 5 million adults age 65 and older, according to the United States Centers for Disease Control and Prevention. And there is currently no way to prevent it or treat it.

Now, new research from New York University College of Dentistry and Weill Cornell Medicine is providing more insights into the Alzheimer disease process. The study, published in Alzheimer and Dementia: Diagnosis, Assessment and Disease Monitoring, has identified a link between periodontal diseases and Alzheimer disease.¹

PLAQUES AND TANGLES

Amyloid beta and tau proteins—which can be measured in cerebral spinal fluid—are key biomarkers for Alzheimer disease. Amyloid beta, thought to be the first protein deposited in the brain as Alzheimer disease develops, clumps together to form plaques. Tau, on the other hand, builds up in the nerve cells to form tangles.

According to the study’s senior author Mony J. de Leon, EdD, professor of neuroscience in radiology and director of the Brain Health Imaging Institute at Weill Cornell Medicine, the study supports the understanding that inflammatory diseases interfere with the clearance of amyloid from the brain. 

THE GOOD AND THE BAD

The study involved 48 older but cognitively normal adults, who underwent oral examinations so that subgingival bacterial samples could be collected. A lumbar puncture was used to obtain cerebral spinal fluid to determine amyloid beta and tau levels in the brain. Lower levels of amyloid beta in the cerebral spinal fluid signaled higher brain amyloid levels, while higher levels of tau in the cerebral spinal fluid indicated higher tangle accumulations in the brain.

Researchers analyzed the DNA of the harmful bacteria extracted from under the gumline, which included Prevotella, Porphyromonas, and Fretibacterium, as well as beneficial bacteria such as Corynebacterium, Actinomyces, and Capnocytophaga. They found that study subjects with more harmful than healthy bacteria were more likely to have reduced cerebral spinal fluid amyloid levels. They, however, did not find an association between gingival bacteria and tau levels, so it’s unclear whether tau lesions will develop later or if the subjects will develop the symptoms of Alzheimer disease. 

As a result of their findings, the researchers formed a hypothesis that high levels of healthy bacteria help maintain bacterial balance and decrease inflammation. Therefore, they may offer a modicum of protection against Alzheimer disease. The study results underscore the importance of maintaining a healthy oral microbiome, which can help keep the good/bad bacterial balance—and hence, amyloid beta levels—in check.

HEALTHY STRATEGIES

Good oral health strategies and regular dental visits will help make this task a little less challenging. Dentifrice, such as fluoride-containing pastes and mouthrinses, along with the use of the appropriate toothbrushes, floss, and/or interdental brushes are certainly beneficial. Additional adjuncts such as products offering dry mouth relief and those allowing patients to see where harmful plaque remains on teeth surfaces can help them stay on top of pathogenic proliferation in the oral cavity.

The researchers plan to conduct a longitudinal study and a clinical trial to test if improving gingival health—through scaling and root planing to remove deposits of plaque and tartar from under the gumline—can modify brain amyloid and prevent Alzheimer disease.

REFERENCE

1. Kamer AR, Pushalkar S, Gulivindala D, et al. Periodontal dysbiosis associates with reduced CSF Aβ42 in cognitively normal elderly. Alzheimers Dement (Amst). 2021;13:e12172.