Diabetes is a known risk factor for mental decline and dementia. Paired with total tooth loss, the potential harm to the brain is even more significant, new research indicates.
The findings highlight the importance of good dental care and diabetes control in aging adults, said Bei Wu, lead author of a new study of nearly 10,000 adults.
"Access to dental care for older adults, especially those with diabetes, is really important," said Wu, vice dean for research at the New York University Rory Meyers College of Nursing and co-director of the NYU Aging Incubator in New York City.
The American Diabetes Association recommends regular dental checkups for anyone with diabetes — "but how many people are following that and how many clinicians are recommending this?" Wu said.
On its own, poor oral health, especially gum disease and tooth loss, has also been linked to cognitive impairment and dementia.
Wu notes that researchers are now beginning to understand how oral health, diabetes and cognitive decline may exacerbate one another.
"We need to raise awareness of this," she said.
Inflammation plays a role in both diabetes and gum disease, the study notes. These inflammatory processes may contribute to declines in reasoning and thinking skills -- so-called cognitive decline.
Poor nutrition is another pathway. Having painful gums and missing teeth can make it difficult to chew healthy food. This can lead to nutritional deficiency. The impaired blood sugar levels and insulin sensitivity found in diabetes can also worsen nutritional deficiency, according to the study.
And certain bacteria related to chronic periodontitis, or gum disease, may also affect cognitive function, Wu said.
To study this in combination, the researchers divided older adults into groupings by age: 65 to 74, 75 to 84 and 85 and older.
The researchers used data from the University of Michigan's Health and Retirement Study for 2006 to 2018, which measured memory and cognition every two years. This included 9,948 older adults.
In adults ages 65 to 84, those with diabetes and complete tooth loss together had the highest rate of accelerated mental decline compared to those with neither condition.
Those with just diabetes ages 65 to 74 or just complete tooth loss ages 65 to 84 also had faster cognitive decline.
But mental decline was fastest in those ages 65 to 74 with both diabetes and total tooth loss.
Researchers did not find conclusive evidence linking mental decline with toothlessness and diabetes in adults ages 85 and older.
They theorized that perhaps the less healthy among this group had already died before their reaching their late 80s. Or it's possible that this age group already had greater cognitive impairment.
Wu noted that the study is observational and can't prove cause and effect.
Cautioning that he is not a diabetes expert, Dr. Cyprien Rivier, a postdoctoral fellow in neurology at Yale School of Medicine, said the connections between diabetes and periodontitis make sense. Rivier was not involved in the study.
Experts are aware that inflammation leads to changes in the microarchitecture of the brain.
"We know that when there are high levels of systemic inflammations, the white matter is getting a bit more disorganized," Rivier said.
This leads to worse brain health and cognitive outcomes, he said.
Mouth health is very important for other areas of the body, including heart health, Rivier noted. For example, the American Heart Association says patients who've had heart valve issues must take antibiotics before certain dental procedures because of bacteria that can travel through the bloodstream.
"The effects of oral health on the whole body are now really well-defined," Rivier said.
More studies are needed to assess these connections, yet good dental health is an easy and important target for improving health, Rivier said.
"It's rather inexpensive. It's pretty easy to improve oral health on a population level," Rivier said.
The study authors say older adults who have poor dental health and diabetes would benefit from cognitive screenings from their primary care providers.
The study findings were published March 12 in the Journal of Dental Research.