Having chronic gum disease gives people a 70% increased risk of developing Alzheimer's, scientists have found.

Research has linked gum problems and dementia for several years. These studies have usually been small in which a snapshot of people's health in time has been taken, rather than large studies tracking their likelihood of developing disease in the long term.

One of the largest longitudinal studies on the topic has now found a strong correlation between gum disease, or periodontitis, and risk of Alzheimer's. The study, published in the journal Alzheimer's Research and Therapy, tracked 9,291 patients with gum disease and 18,672 control patients without gum disease over 16 years.

After controlling for factors such as age, sex and whether they lived in a city or the countryside, having gum disease throughout the period led to the 70% increased risk.

"These findings highlight the need to prevent progression of periodontal disease and promote healthcare service at the national level," study author Chang-Kai Chen and colleagues from the Chung Shan Medical University in Taiwan wrote in the paper.

As well as an increased risk of dementia, people with chronic gum disease were also at a higher risk of depression and high cholesterol, among other conditions. These associations, as well as an increased risk of diabetes and heart disease found in previous studies, are thought to relate to the body's inflammatory response to gum disease.

The present study established a link but it did not establish causes – so it's too soon to say that brushing your teeth properly could stop you getting Alzheimer's. But it certainly wouldn't hurt for several reasons, said periodontologogist Mark Ide at King's College London, who was not involved in the research.

"People who have higher levels of those inflammation markers than those who don't. We think if we treat gum disease in people effectively, we can reduce that systemic inflammation ," Ide told IBTimes UK.

So reducing the body's inflammatory response by treating gum disease could ease the risk of Alzheimer's. However, there could be other confounding factors that complicate the relationship between the two.

"It could be that people with impaired cognitive function are less likely to take care of themselves, and so are more likely to develop gum disease," Ide said.

To understand the relationship more, Ide is currently carrying out an intervention study. This will determine whether removing gum disease from the equation can reverse mild cognitive impairment.