In 2010, researchers from New York University (NYU) concluded that there is a link between gum inflammation and Alzheimer's disease, after reviewing 20 years of data on the association.
However, the number of participants in the NYU study was fairly small. The researchers analyzed data from 152 subjects enrolled in the Glostrop Aging Study - a study looking at psychological, medical and oral health in Danish men and women. The study spanned a 20-year period and ended in 1984, when the subjects were all over the age of 70.
Comparing cognitive function at ages 50 and 70, the NYU team found that gum disease at the age of 70 was strongly associated with low scores for cognitive function.
Study participants were nine times more likely to have a score in the lower range of the cognitive test - the "digit symbol test" (DST) - if they had inflammation of the gums.
Although this study took into account potentially confounding factors like obesity, cigarette smoking and tooth loss unrelated to gum inflammation, there was still a strong association between low DST score and gum inflammation.
In 2013, UK-based researchers from the University of Central Lancashire (UCLan) built on the findings of this study, by comparing brain samples from 10 living patients with Alzheimer's with 10 brain samples from people who did not have the disease.
Analysis showed that a bacterium - Porphyromonas gingivalis - was present in the Alzheimer's brain samples but not in the samples from the brains of people who did not have Alzheimer's. What was interesting was that P. gingivalis is usually associated with chronic gum disease.
The team followed up this research in 2014 with a new mouse study, the results of which were published in the Journal of Alzheimer's Disease. Medical News Today spoke to co-author Dr. Sim K. Singhrao regarding the findings.
Dr. Singhrao says that there is sufficient scientific evidence to show that two of the three gum disease-causing bacteria are capable of motion (or "motile") and have been consistently found in brain tissue.
"These motile bacteria can leave the mouth and enter the brain via two main routes," he explains. "They can use their movement capability to directly enter the brain. One of the paths taken is to crawl up the nerves that connect the brain and the roots of teeth. The other path is indirect entry into the brain via the blood circulation system."
In a patient who has bleeding gums, says Dr. Singharo, the gum disease-causing bacteria will enter the blood stream every time they clean their mouth and even when they eat food.
"P. gingivalis is particularly interesting as it has found ways to hitch a lift from red blood cells when in the blood stream and instead of getting 'off the red blood cell bus' in the spleen, they choose to get off in the brain at an area where there are no immune checkpoints. From there, they spread to the brain at their will. In addition, in older individuals, the blood vessels tend to enlarge and become leaky."
"The published work confirmed P. gingivalis placed in the mouths of mice finds its way to the brain once gum disease becomes established first," Dr. Singhrao concludes. "Furthermore, our hypothesis is strengthened by the recent results demonstrating that the chemicals released by the brain's immune system in response to P. gingivalis reaching the brain 'inadvertently' damage functional neurons in the area of the brain related to memory."