Considering the unseen links to Alzheimer’s: Gingivitis

 

By Tré LaRosa
NeuLine Health

According to the Alzheimer Association’s annual report Alzheimer’s Disease Facts and Figures, “an estimated 6.2 million Americans age 65 and older are living with Alzheimer’s dementia in 2021.” This number is expected to more than double to 12.7 million by the year 2050. By comparison, New York City’s population is projected to be 9 million in 2050. Alzheimer’s is prevalent and its incidence is increasing and yet, the National Institute of Aging reports that scientists still don’t fully understand the cause of the majority of Alzheimer’s disease cases.

So what are some of the unseen links to Alzheimer’s and what does the evidence suggest? In this blog, we’re going to evaluate the evidence of links between Alzheimer’s and gingivitis. In future blogs, we’ll talk about other factors that have been linked to Alzheimer’s including air pollution, diet, and exercise. But before we evaluate these potential causes of Alzheimer’s, a few things to consider:

  • Correlation does not imply causation. This is a cliché in science but it’s a critical point and can be easily illustrated and explained through a famous if strange example of the phenomenon: the positive correlation of increasing ice cream sales and murders in New York City. If correlation were to imply causation then it would suggest that people purchasing ice cream somehow results in people committing more murders. Instead, maybe both of these are the result of something else, say increasing temperatures, that just so happens to be a mechanism for both. Anyhow, this important point should be remembered when considering links to Alzheimer’s.
  • If a factor is linked to Alzheimer’s, that is, there is a positive correlation between a certain factor and Alzheimer’s, then theoretically removing or altering that factor should decrease the rate of those with Alzheimer’s. It’s important to remember this as this is how scientists test hypotheses. In the case above, if you were to suddenly enact laws that reduced access to ice cream while doing nothing else (as in the temperature fluctuations remain the same), it is unlikely that murders would immediately decrease. That’s due to the fact that the fundamental explanation for more murders was not due to ice cream sales but rather a different causative explanation: increasing temperatures. This doesn’t mean simply understanding the fundamental cause will allow for easy solutions to prevent it, but understanding root causes allow for scientists and doctors to better diagnose, prevent, and treat Alzheimer’s disease.

With the above considerations in mind, let’s first consider gingivitis.

Gingivitis and Alzheimer’s Disease

Gingivitis is a mild form of gum disease due to poor oral hygiene that results in plaques developing on teeth which triggers inflammations of the gum tissues. Poor oral hygiene combined with the over 700 species of bacteria present in the mouth can result in the development of gingivitis.

It has been debated for years that perhaps periodontal disease may cause Alzheimer’s but as mentioned above, positively demonstrating causation for a disease that is still far from totally understood is challenging. In 2020, National Institute of Aging scientists conducted an analysis that found “bacteria that cause gum disease are also associated with the development of Alzheimer’s disease.”

How could this be? Well, these researchers propose that the bacteria that can cause infections in the mouth may enter the bloodstream and end up in the brain where, as the article eloquently puts it: “Previous lab studies suggested that this is one mechanism influencing the cascade of events (emphasis added by author) that leads to dementia.” The bolded phrase is an important reminder that teasing out an exact and single cause for any sort of dementia is difficult and unlikely, but understanding potential links is important as it helps researchers position their experiments to determine causative factors and whether modifying potential causative factors can help to prevent Alzheimer’s or, at the very least, slow progression.

Perhaps the most compelling point from this study was the bacteria that researchers found as the most frequent cause of gum disease: P. gingivalis. In a different study, researchers suggest that “plaques of beta-amyloid protein, a major hallmark of Alzheimer’s disease, may be produced as a response to this [P. gingivalis] infection.” 

Here we find ourselves at the intersection of correlation and causation yet again. Research will be ongoing, including another recent study showing “increases in ‘bad’ bacteria and increases in ‘good’ bacteria associated with amyloid beta.” The implications here are that there may be upstream factors, such as oral hygiene combined with a ratio of so-called “good” and “bad” bacteria in the mouth, that can either prevent the development of Alzheimer’s or, if imbalanced, can directly cause Alzheimer’s disease.

Conclusions

Alzheimer’s disease in its complexity poses a problem for researchers that is less common in other fields of biomedical research. For genetic diseases like cystic fibrosis or sickle-cell anemia, which are also complex, there is a firm understanding in the cause of these diseases, although its clinical presentation and pathophysiology can certainly look different across the patient community. Alzheimer’s, which does have a genetic component, has a constellation of different factors that appear to increase one’s risk for developing the disease, as well as a constellation of different symptoms and prognoses.

Based on the few studies discussed above, can we affirmatively say that gingivitis causes Alzheimer’s? I hesitate to say we can say that, but I think it’s reasonable to say there appears to be something very interesting and worth further investigating in the associations between gum disease, oral bacteria, and Alzheimer’s dementia. We can confidently say that those with gum disease appear to be more at risk for developing Alzheimer’s. Whether or not this changes how scientists should treat Alzheimer’s after diagnosis, I’m not sure, but from a purely risk factor perspective combined with the incidence of gum disease, it’s clear that we shouldn’t take gum disease lightly. After all, nearly 65 million Americans over the age of 30 have periodontitis. This research does not claim that these Americans will all develop Alzheimer’s but they may be more likely to develop the disease compared to those who don’t have gum disease. As periodontitis itself can lead to other downstream issues, it seems like a reasonable public health concern to work to reduce periodontitis.

The current research is clear that Alzheimer’s is a clinical syndrome that affects those who suffer from it in a variety of ways and due to the assortment of different risk factors, it’s critical to remember that the full-scape approach to Alzheimer’s should be considered multi-disciplinary and from the lenses of prevention, diagnosis, and treatment.

In subsequent evaluations of the unseen links to Alzheimer’s, we’ll consider air pollution, diet, and exercise.

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