Bad teeth and bleeding gums can be a sign of decline of thinking among the middle-aged, a new study contends, Newsmax Health reports. 

"We were interested to see if people with poor dental health had relatively poorer cognitive function," said study co-author Gary Slade, a professor in the department of dental ecology at the University of North Carolina at Chapel Hill.

"What we found was that for every extra tooth that a person had lost or had removed, cognitive function went down a bit," Slade said.

"The same was true when we looked at patients with severe gum disease," he said.

To explore a potential connection between oral health and mental health, the authors analyzed data gathered between 1996 and 1998 that included tests of memory and thinking skills, as well as tooth and gum examinations, conducted among nearly 6,000 men and women. All the participants were between the ages of 45 and 64.

Roughly 13 percent of the participants had no natural teeth, the researchers said. Among those with teeth, one-fifth had less than 20 remaining. More than 12 percent had serious issues with gums.

The researchers found that scores on memory and thinking tests were lower by every measure among those with no teeth or fewer teeth and serious gum bleeding when compared to those who had teeth and better gum health.

Slade said. "It could be that poor oral health might lead to the avoidance of certain foods, thereby contributing to cognitive decline."

"It could also be that dental disease, especially gum disease, gives rise to inflammation not only in the gums but throughout the circulatory system, ultimately affecting cognition," he said.

"There might be a genetic link between the two diseases," said Catherine Roe, an assistant professor of neurology at the Washington University School of Medicine, in St. Louis,. "Or, of course, it could simply be that if you've got cognitive problems you just aren't taking very good care of your teeth."