The mouth is home to about 700 species of bacteria, including those that can cause periodontal (gum) disease. A recent analysis led by NIA scientists suggests that bacteria that cause gum disease are also associated with the development of Alzheimer’s disease and related dementias, especially vascular dementia. The results were reported in the Journal of Alzheimer’s Disease.
Gum disease results from infection of the oral tissues holding teeth in place. Bleeding gums, loose teeth, and even tooth loss are the main effects of this disease. Bacteria and the inflammatory molecules they make can travel from infections in the mouth through the bloodstream to the brain. Previous lab studies have suggested that this is one mechanism influencing the cascade of events that leads to dementia, but large studies with people have not been conducted to confirm this relationship.
The NIA Intramural Research Program team used nationally representative, publicly available data from the National Health and Nutrition Examination Survey (NHANES), a large population study performed by the CDC’s National Center for Health Statistics. The team examined whether gum disease and infections with oral bacteria were linked to dementia diagnoses and deaths using restricted data linkages with Medicare records and the National Death Index. The team compared different age groups at baseline, with up to 26 years of follow-up, for more than 6,000 participants.
The NHANES participants had received a dental exam for signs of gum disease. In addition, the participants received blood tests for antibodies against causative bacteria. The team analyzed antibodies against 19 oral bacteria for an association with the diagnosis of Alzheimer’s, diagnosis of any kind of dementia, and death from Alzheimer’s. Of these 19, Porphyromonas gingivalis is the most common culprit of gum disease. In fact, a recent study suggests that plaques of beta-amyloid protein, a major hallmark of Alzheimer’s disease, may be produced as a response to this infection.
The analysis revealed that older adults with signs of gum disease and mouth infections at baseline were more likely to develop Alzheimer’s during the study period. Among those 65 years or older, both Alzheimer’s diagnoses and deaths were associated with antibodies against the oral bacterium P. gingivalis, which can cluster with other bacteria such as Campylobacter rectus and Prevotella melaninogenica to further increase those risks.
A long-term follow-up for this study is needed because the findings suggest that oral infection preceded the diagnosis of dementia. After all, having dementia makes it more likely that an individual will not be able to brush and floss effectively, which increases the likelihood of such infections and gum disease. In any case, it is important to keep in mind that population studies can show association but not causality. The authors emphasize that clinical trials are needed to test whether treating infections with P. gingivalis can reduce the development or symptoms of dementia.
This research was supported entirely by the NIA Intramural Research Program.
Reference: Beydoun M, et al. Clinical and bacterial markers of periodontitis and their association with incident all-cause and Alzheimer’s disease dementia in a large national survey. Journal of Alzheimer’s Disease. 2020;75(1):157-172. doi: 10.3233/JAD-200064.