Older adults with more harmful than healthy bacteria in their gums are more likely to have evidence for amyloid beta – a key biomarker for Alzheimer’s disease – in their cerebrospinal fluid (CSF), according to new research from the New York University College of Dentistry and Weill Cornell Medicine. However, this imbalance in oral bacteria was not associated with another Alzheimer’s biomarker called tau.
The study, published in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, adds to the growing evidence of a connection between gum disease and Alzheimer’s.
Lead study author Angela Kamer said: “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. 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 researchers studied 48 healthy, cognitively normal adults aged 65+. Participants underwent oral examinations to collect bacterial samples from under the gumline, and lumbar puncture was used to obtain CSF in order to determine the levels of amyloid beta and tau. To estimate the brain’s expression of Alzheimer’s proteins, the researchers looked for lower levels of amyloid beta (which translate to higher brain amyloid levels) and higher levels of tau (which reflect higher brain tangle accumulations) in the CSF.
The results showed that individuals with an imbalance in bacteria, with a ratio favouring harmful to healthy bacteria, were more likely to have the Alzheimer’s signature of reduced CSF amyloid levels.