Could regular flossing be the key to preserving your brain health in later life?
This may sound unlikely, but the connection between the microbes residing in your mouth and cognitive decline represents one of the most fascinating new frontiers in dementia research.
A growing number of studies have identified a significant link between oral hygiene and dementia risk.
In 2016 neuroscientists studying a small group of patients with mild to moderate symptoms of dementia found that those with periodontitis, severe gum disease driven by an overgrowth of inflammatory bacteria in the mouth, were experiencing far greater rates of cognitive decline.
Four years later, researchers in the US published a study in the Journal of Alzheimer’s Disease showing that older adults with signs of gum disease and mouth infections were more likely to develop Alzheimer’s.
And in 2022, a review of 47 different studies on the subject, published in the Journal of the American Geriatrics Society, concluded that poor oral health is associated with brain degeneration over time.
So, what is going on? Dr Eamon Croke, president of the Irish Dental Association, explains there are up to 20bn bacteria and 700 different types of microorganisms in the mouth.
Fluctuations in our diet and other habits, such as alcohol use, smoking, and irregular brushing, can all have a significant impact on which species tend to flourish and our ability to keep their numbers in check.
“Good oral hygiene along with regular professional assessments to detect and manage disease is important to controlling the total bacterial load in our bodies,” says Croke.
“The increase in total body load of oral pathogens is potentially harmful to multiple tissues and organs, including the brain.”
We now know that oral microbes can work their way from the mouth into the bloodstream, where they can reach organs ranging from the gut to the heart, joints, and placenta, which is why poor oral health has also been associated with an increased risk of irritable bowel syndrome, diabetes and heart disease.
But the microbes can also reach the brain, and bacteria, which are single-celled microbes, such as porphyromonas gingivalis (P gingivalis), one of the drivers of periodontitis, have been identified within beta-amyloid plaques taken from autopsies of Alzheimer’s patients.
Scientists are still undecided as to whether these bacteria can actually instigate neurodegeneration, while another theory suggests they may contribute to cognitive decline by driving inflammation in the bloodstream.
Over many years, this inflammatory assault may ultimately weaken the blood-brain barrier (the protective layer of cells which protects the bloodstream and brain tissue), allowing inflammatory toxins to penetrate and damage the brain.
Croke says that people with poor oral health have been shown to have increased damage to the delicate architecture of various brain regions.
“In recent years, research has examined the impact inflammation may have on the development of dementia,” says Dr Aoife Fallon, consultant geriatrician at Tallaght University Hospital (TUH), who studies the link between oral and brain health.
“It is also thought that chronic inflammation could affect the production, deposition and clearance of amyloid, increasing the risk of Alzheimer’s disease and dementia.”