Gum Disease is Linked to Alzheimer’s

Activating Microglia in the Brain

The link between gum disease, or periodontal disease, and dementia has been known for a while.

One theory has been that increased inflammatory cytokines in the gums — chronic inflammation – caused the increased risk of dementia. A recent review of five previous studies found that there were a couple of specific oral bacteria linked to increased Alzheimer’s, as well as an overall increased risk of Alzheimer’s in elderly people with periodontal disease. The specific oral bacteria were also found in the central nervous system, pointing to both the role of pathogens as well as overall increased inflammation.[ref] For example, researchers have found Porphyromonas gingivalis, a key bacteria in periodontitis, in the brains of Alzheimer’s patients.[ref]

There’s a recent study that explains the role of specific oral pathogens in Alzheimer’s disease.

The researchers used a mouse model of periodontal disease to show a direct link between periodontal disease and neuroinflammation.

Alzheimer’s disease has been associated with neuroinflammation mediated by the brain’s immune cells, microglia. Microglia are vital to the brain’s immune and inflammatory response and are responsible for engulfing harmful substances, such as the beta-amyloid plaques found in AD as well as taking care of any pathogens that cross the blood-brain barrier.

In this study, scientists induced periodontal disease in the mice. As the oral inflammation developed, researchers found significant bone loss, increased inflammation —  and an upsurge in activated microglia in the brain by day 30.

They discovered that specific periodontal disease-associated bacteria could stimulate microglia, leading to an increased inflammatory response and upregulation of receptors involved in phagocytosis. Specifically, exposure to Klebsiella variicola, a bacteria that causes periodontal disease in mice, significantly increased the microglial activation. The researchers used heat-killed bacteria, which activated the microglia through TLR receptors. (In other words, it wasn’t an active bacterial infection. Instead, the microglia recognize parts of the dead bacteria and are activated from that.)

Activating microglia and causing more phagocytosis, including phagocytosis of amyloid-beta plaque, sounds like it could be a good thing. It’s clearing out the plaque…  However, researchers think that the amyloid-beta plaque has been deposited for a reason, and in the older brain, the activation of microglia and the complement system (another part of the immune response) can actually cause more damage to the synapses of the neurons. [ref – open source, good overview]

What can you do with this information? 

Oral health is important to the brain and to the heart. Avoiding getting bacteria from the mouth into the bloodstream is important.

Genetics plays a big role in who is likely to get gingivitis or periodontal disease. You can read all about genes and periodontal disease on Genetic Lifehacks.

So what can you do to prevent the puffy gums that bleed when you floss or poke them with sharp dentist tools? Reducing an overactive inflammatory response in the gum line may help to keep it from bleeding when brushing and flossing. Read the Genetic Lifehacks article on periodontal disease linked above. There are specific ways to reduce inflammatory cytokines based on which genetic variants you carry.

Should you floss?
Research shows that flossing more often than once a week is very slightly associated with a decreased risk of periodontal disease.[ref] (I was surprised at how slight the benefit was for flossing.)

Bacteria in the bloodstream is found for a short period in about 40% of people (both with and without periodontal disease) after flossing with dental floss.[ref] Your immune system takes care of the bacteria if you are healthy.

A water flosser (e.g. water pik) is another option. Research shows that it effectively reduces dental plaque in people with gingivitis.[ref]

Should you just kill off all bacteria in your mouth with strong anti-bacterial mouthwash? Well, that also kills the beneficial oral microbes. Some oral microbes are effective at preventing oral pathogens.[ref]

Instead, you may want to rinse with green tea. A clinical trial found that green tea was more effective in preventing plaque buildup than chlorhexidine or salt water.[ref]

Low vitamin C is associated with an increased risk of periodontitis.[ref] Taking vitamin C reduces bleeding when brushing and flossing (but doesn’t cure gingivitis).[ref] So make sure you are getting plenty of vitamin C-rich foods – or take a vitamin C supplement.

Quercetin and Resveratrol: Studies show that resveratrol and curcumin specifically reduce the progression of periodontitis.[ref][ref]