Could taking good care of gums and teeth also help to protect the brain? A recent study has added to growing evidence of a link between severe gum disease, or periodontitis, and a raised risk of dementia. Using data from an extensive national health insurance screening program, investigators from Seoul National University in South Korea examined the relationship between chronic periodontitis and dementia.

In a paper that now features in the Journal of the American Geriatrics Society, the researchers describe how they found a modest link between severe gum disease and dementia, which is consistent with some previous studies. The researchers also point out that their "retrospective cohort study" is likely the first to establish that lifestyle factors, such as alcohol consumption, smoking, and exercise, did not appear to have any effect on the connection.

The term dementia describes a decline in mental capacity—such as increasing difficulty with memory and reasoning—that becomes so severe that it disrupts daily living. Alzheimer's disease is the most common cause of dementia.

Need to reduce dementia risk factors

A joint 2012 report by the World Health Organization (WHO) and Alzheimer's Disease International stated that dementia is a global "public health priority." The report stated that there were 35.6 million people worldwide living with dementia in 2012. It also estimated that the global prevalence of dementia would increase three-fold by 2050. In their study paper, the researchers discuss the potential impact that reducing dementia risk factors could make to this projected massive burden.

The researchers cite a 2014 study that suggested that decreasing dementia risk factors by 20% could reduce the anticipated 2050 prevalence of dementia by more than 15%. "One such risk factor," they suggest, "is chronic periodontitis." Periodontitis is a common human disease in which the gums and the structures that support the teeth become inflamed due to bacterial infection. It usually starts as gingivitis, or inflammation of the gums.

Although the human mouth is home to a wide range of bacteria, when conditions are right, the bacteria populations can increase dramatically to cause inflammation. This usually happens when bits of food and bacteria deposit on tooth surfaces to form plaque. The bacterial colonies in the plaque grow and produce toxins that trigger inflammation responses in the gums. If untreated, the inflammation becomes persistent and destroys bone, causing tooth loss.

Higher risk of developing dementia

Several animal and human studies have suggested links between chronic periodontitis and dementia. The authors of the new study refer to a retrospective investigation that found participants with chronic periodontitis had a "significantly higher risk" of developing Alzheimer's disease than those without it. However, they also note that these previous studies have been limited by small sample sizes, and by the fact that they did not consider forms of dementia outside of Alzheimer's disease.

For the new investigation, the team analyzed 2005–2015 health data on 262,349 people aged 50 and older from South Korea's National Health Insurance Service-Health Screening Cohort. The analysis revealed that people who had received a diagnosis of chronic periodontitis had a 6% higher risk of developing dementia than those who had not. The risk was particularly significant for those who developed Alzheimer's disease.

Due to the study's design limitations, the findings cannot prove that periodontitis causes dementia; they can only suggest a link. This leaves open the possibility of reverse causality. For example, could it be that pre-diagnosed early stages of dementia cause lapses in oral hygiene that lead to gum disease?

Three potential biological explanations

If, however, the causal direction should be that periodontitis leads to dementia, the authors propose three biological ways in which it could come about. The first mechanism through which periodontitis could cause dementia would involve bacteria from the infected gums entering the bloodstream and then crossing the blood-brain barrier into the brain. These could then trigger brain tissue inflammation and even spur production of the toxic proteins that are hallmarks of Alzheimer's disease. Medical News Today recently reported research that makes a convincing case for such a causal link. In that study, researchers revealed that Porphyromonas gingivalis, a bacterium that drives gum disease, can also be present in the brains of people with Alzheimer's disease.

The second mechanism would be a similar process in that the gum infection could set up a "systemic inflammatory state" that releases agents that promote inflammation. These agents could also cross the blood-brain barrier to trigger inflammation in brain tissue, which, if prolonged, can also contribute to toxic protein buildup.

The researchers suggest that the third mechanism would occur through damage to the lining of blood vessels. They note that evidence from previous research showed that such damage has ties to an increase in toxic proteins in the brain. The authors write:

"In conclusion, [chronic periodontitis] appeared to be associated with increased risk for dementia even after taking into consideration lifestyle behaviors including smoking, alcohol intake, and physical activity."

They call for further research to look into whether the prevention and treatment of chronic periodontitis could reduce the risk of developing dementia.

In a short editor's note, Joseph G. Ouslander, MD, and Mary Ganguli, MD, MPH, comment that these findings, "in combination with the recently published report on P. gingivalis, should make us all think more seriously about optimizing our own and our patients' oral hygiene practices and dental care, with the added potential of perhaps protecting our brain health as well."