A new study from Japan is the latest to find a link between gum disease and a higher risk of dementia and brain shrinkage.

A causal link has not yet been established between good dental hygiene and progressive brain death. But studies are repeatedly finding an association.

Part of brain where memories are formed

Research from the Division of Ageing and Geriatric Dentistry at Tohoku University, Japan, found that “gum disease and tooth loss were linked to shrinkage in the hippocampus”.

The hippocampus is a small, vulnerable part of the brain involved in long-term memory formation and memory retrieval. It is also part of the limbic system regulating motivation, emotion and learning.

The study

The study recruited 172 people, average age of 67, who showed no cognitive decline.

In the first phase of the study, participants had their gums examined. A probe was used to establish severity of disease. Participants also had their teeth counted. And they took memory tests to establish their cognitive health.

Their brains were scanned by MRI scans in order to measure volume of the hippocampus at baseline. They were scanned again four years later.

Hippocampal atrophy is an early characteristic of Alzheimer’s disease and other forms of dementia.

Researchers found that the degree of tooth loss and the severity of gum disease were correlated with the pace and degree of brain shrinkage.

Mild gum disease ages the brain by a year

After adjusting for age, the researchers found that “for people with mild gum disease, the increase in the rate of brain shrinkage due to one less tooth was equivalent to nearly one year of brain ageing”.

For people with severe gum disease the increase in brain shrinkage due to one less tooth was equivalent to 1.3 years of brain ageing.

“The findings suggest that retaining teeth with severe gum disease is associated with brain atrophy,”said study author Dr Satoshi Yamaguchi.

Supported by previous research

A 2021 study from New York University found that tooth loss is a risk factor for cognitive impairment and dementia. With each tooth lost, the risk of cognitive decline grows.

However, this risk was not significant among older adults with dentures, suggesting that timely treatment with dentures may protect against cognitive decline.

An intriguing 2016 study suggested that Alzheimer’s and gum disease work in concert, essentially causing each condition to worsen.

University of Hampton and King’s College London researchers observed that gum disease is common in older people and may become more common in Alzheimer’s disease. They suggest this is because of a reduced ability to take care of oral hygiene as the disease progresses.

Higher levels of antibodies to periodontal bacteria (the body’s response to gum disease) are associated with an increase in levels of inflammatory molecules elsewhere in the body. This in turn has been linked, in previous studies, to greater rates of cognitive decline in Alzheimer’s disease.

In a small observation study – involving participants with mild to moderate Alzheimer’s disease – the researchers found that the presence of gum disease at baseline “was associated with a six-fold increase in the rate of cognitive decline in participants over the six-month follow-up period of the study”.

The authors concluded that gum disease is associated with an increase in cognitive decline in Alzheimer’s Disease. This occurs possibly via mechanisms linked to the body’s inflammatory response.

Professor Clive Holmes, senior author from the University of Southampton, said:

“If there is a direct relationship between periodontitis and cognitive decline, as this current study suggests, then treatment of gum disease might be a possible treatment option for Alzheimer’s.”

What’s going on here?

Unhealthy oral bacteria cover the teeth and gums in a film. This film is what the dentist calls plaque.

It’s plaque that causes gum disease in the form of inflammation, weakening a tooth’s connection to the jaw. There’s good evidence that this bacterial inflammation spreads through the body via the bloodstream.

There is abundant research that suggests this inflammation potentially causes damage to the brain (dementia and strokes), the heart (heart attacks and vascular inflammation) and bowel (colon cancer).