A study has found that people with poor oral hygiene or gum disease could be at higher risk of developing Alzheimer’s compared with those who have healthy teeth.

Researchers from the University of Central Lancashire (UCLan) in the UK, discovered the presence of a bacterium called Porphyromonas gingivalis in the brains of patients who had dementia when they were alive. The bug is usually associated with chronic periodontal (gum) disease.

For the study, published in the Journal of Alzheimer’s Disease, 10 brain samples from patients with dementia were donated for analysis by a scheme called Brains for Dementia Research, alongside 10 brain samples from people who had not had the disease.

Examination of the samples revealed the presence of the Porphyromonas gingivalis in the samples of the brains affected by Alzheimer’s.

This bacteria is usually found in oral cavities, and enters the blood stream through a variety of daily activities, such as chewing, eating and brushing teeth. However, it is more likely to enter the blood stream after invasive dental treatment, where it is possible that the bacteria can enter the brain regularly, the researchers say.

Each time the bacteria enter the brain, the researchers note, this could potentially trigger immune system responses, causing the release of excess chemicals that can kill neurons.

The researchers say that this activity could lead to symptoms such as confusion and deteriorating memory – typical symptoms of Alzheimer’s disease.

The study adds to previous findings that Alzheimer’s is linked to poor oral health. Research from New York University in 2010 revealed long-term evidence that linked gum inflammation and Alzheimer’s disease, finding that gum disease could increase the risk of cognitive dysfunction.

Another study has suggested that other bacteria and viruses are linked to the disease. Research from the University of New Mexico suggested that Herpes simplex virus type 1 (HSV-1) was linked to Alzheimer’s. See “Cold sores” connected to cognitive decline.

Professor St John Crean, from the School of Medical Dentistry at UCLAN, says of this most recent research:

Whereas previous studies have indicated a link between dementia and other bacteria and viruses such as the Herpes simplex virus type 1, this new research indicates a possible association between gum disease and individuals who may be susceptible to developing Alzheimer’s disease, if exposed to the appropriate trigger.”

“Research currently under way at UCLan is playing an active role in exploring this link,” Prof. St John Crean continues, “but it remains to be proven whether poor dental hygiene can lead to dementia in healthy people, which obviously could have significant implications for the population as a whole. It is also likely that these bacteria could make the existing disease condition worse.”

The researchers hope that continued donation of brain tissue will enable examination of more samples from people with and without Alzheimer’s disease who have relevant dental records.

They add that future research will involve determining whether the Porphyromonas gingivalis could be used as a marker for a blood test that predicts the development of Alzheimer’s disease in patients who are at higher risk.