Remember the children’s song that goes, “the shin bone is connected to the knee bone; the knee bone is connected to the thigh bone …?” How about a modern update? “The gum bacteria are connected to the brain tissue.” A recent study now connects a bacterium associated with gum disease and Alzheimer’s dementia.

Alzheimer’s is a significant public health problem in the U.S. There are 5.7 million people living in the U.S. with Alzheimer’s in 2018, and it’s the sixth leading cause of death in the U.S. One in three Americans 65 and older will develop this disease. Alzheimer’s progressively robs a person of their identity, and the costs for caring for the health needs of those afflicted is estimated at $277 billion in 2018. In our home state, Texas, the number of people with Alzheimer’s aged 65 or older in 2018 was around 380,000, and the number is increasing.

Porphyromonas gingivalis, or P. gingivalis, is a bacterium that causes gum disease in your mouth. That name is a mouthful — pun intended. It’s a bacterium that hates oxygen and causes periodontal disease. Periodontal disease can destroy gum tissue, lead to the loss of teeth, and cause other issues. The bacterium lives deep in the tissue that makes up the gums — those pockets they measure at your annual dental exam.

The inflammation caused by periodontal disease can also cause problems with your heart and blood vessels. The bacterium makes your immune system produce chemicals that change blood vessel cells and increase fatty deposits and platelets in the cardiovascular system. This leads to plaque buildup and eventually results in atherosclerosis (hardening of the arteries) and cardiovascular disease. New research shows that a protein made exclusively by P. gingivalis can be found in the brains of patients with Alzheimer’s.

While we understand much about the impact of Alzheimer’s on our population, little is known about exactly how Alzheimer’s starts or how it progresses. In this study, researchers found a P. gingivalis protein called gingipain in the brain tissue of those with Alzheimer’s, which may play a direct role in the disease. The scientists infected gum tissue of mice with this bacterium and found the gingipain protein from the bacterium associated with dead and dying nerve cells in the brains of the mice. There were also higher levels of a protein called β-amyloid that’s associated with Alzheimer’s. Most interestingly, the mice showed signs of dementia.

Additional studies in the lab showed that gingipain damaged a protein called tau that develops into tangles and is also associated with Alzheimer’s dementia. The researchers also used a chemical which inactivates gingipain, and it reduced both β-amyloid levels in the brain and other signs of dementia.

This work points to a bacterium, P. gingivalis, as a source of Alzheimer’s dementia. This could lead to new ways to limit the onset and progression of this cruel disease. For now, it seems like a wise investment to pay attention to your oral health.

Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at

(1) comment

Charlotte O'rourke

Very interesting article.

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