First study author Dr. Mark Ide, from the Dental Institute at King's College London in the UK, and colleagues publish their findings in the journal PLOS One.

According to the Centers for Disease Control and Prevention (CDC), almost half of adults in the US have some form of gum disease, or periodontal disease. Rates increase with age, with the condition affecting more than 70% of adults aged 65 and older.

The researchers note that rates of gum disease may be even higher for people with Alzheimer's disease, primarily because they are less likely to engage in good oral hygiene as their condition progresses.

Previous studies have also associated gum disease with increased risk of developing Alzheimer's. Medical News Today reported on one such study in 2013, in which researchers identified bacteria related to gum disease - Porphyromonas gingivalis - in brain samples of people with Alzheimer's.

For this latest study, Dr. Ide and colleagues looked at whether gum disease may impact the severity of cognitive decline among people with Alzheimer's.

Gum disease linked to six-fold increase in rate of cognitive decline

The team enrolled 59 participants with mild to moderate Alzheimer's disease to their study, and 52 of these participants were followed for an average of 6 months.

At the beginning and end of the follow-up period, the dental health of the subjects was assessed by a dental hygienist, and the researchers took blood samples from the participants and assessed them for inflammatory markers.  Subjects also underwent cognitive tests at study baseline and after 6 months.

Compared with participants who did not have gum disease at study baseline, those who did were found to have a six-fold increase in the rate of cognitive decline during the 6-month follow-up period.

What is more, subjects who had gum disease at study baseline showed an increase in blood levels of pro-inflammatory markers over the follow-up period.

Based on their findings - and those of previous research - the team suggests that gum disease may increase the rate of cognitive decline by increasing the body's inflammatory response.

"A number of studies have shown that having few teeth, possibly as a consequence of earlier gum disease, is associated with a greater risk of developing dementia," says Dr. Ide, adding:

"We also believe, based on various research findings, that the presence of teeth with active gum disease results in higher body-wide levels of the sorts of inflammatory molecules which have also been associated with an elevated risk of other outcomes such as cognitive decline or cardiovascular disease.

Research has suggested that effective gum treatment can reduce the levels of these molecules closer to that seen in a healthy state."

The researchers recognize that the small number of participants in their study is a limitation, and they recommend that the association between gum disease and cognitive decline is investigated in a larger cohort.

Further studies, they say, should also seek to determine the exact mechanisms by which gum disease drives cognitive decline.