A number of papers in recent years have suggested there to be a link between gum disease (periodontitis) and neurodegeneration. Similarly to the correlation with heart disease, it is thought that the underlying mechanism is raised chronic inflammation deriving from toxins released into the bloodstream by the bacteria that cause gum disease. Some epidemiological data suggests that the effect size is modest at best, however - a 6% increase in risk in one cohort, for example. So is there in fact a meaningful link between inflammatory gum disease and forms of neurodegeneration that are thought to be driven in large part by the chronic inflammation of aging? The hypothesis seems reasonable, but as today's open access paper notes, the evidence to date is just not that great.
This is often the way of things in research into the contributing mechanisms of age-related diseases. Having gingival bacteria release immune-provoking compounds into the bloodstream sounds like something to be avoided, and one can find plenty of evidence for this mechanism to exist. The bacteria are definitely there in the mouth, the immune response to their presence established in various ways. But is it causing enough harm in comparison to all of the other damage and dysfunction of an aged metabolism to be influential outside the local issue of gum disease?
Perhaps, perhaps not; the epidemiological data as it stands isn't enough for a concrete conclusion when taken collectively. This may be a case of where there is smoke there is fire, and better and larger studies would produce conclusive outcomes, but it is hard to say in advance. Nonetheless, it is near universally agreed that maintaining as low a level of chronic inflammation as possible with advancing age is a good idea.
Some inflammatory diseases, such as periodontitis, might represent a factor that can contribute to central nervous system (CNS) damage. Periodontitis is a multifactorial chronic inflammatory disease that affects the supporting tissues around the teeth, triggered by dysbiotic biofilms that can lead to systemic inflammation. Periodontal disease is one of the most frequent causes of tooth loss, and is highly prevalent in adults affecting about 20-50% of the global population. It can lead to a systemic inflammatory state through mechanisms that include the spread of pro-inflammatory cytokines and/or bacteria located in the oral cavity. Persistent systemic inflammation/infection can cause neuroinflammation in the brain. Considering this possible interaction, the present study aims to systematically review the evidence supporting the association between the presence of some neurodegenerative disease and periodontitis.
From 534 articles found in this systemic review, 12 were included, of which eight were case-control, three were cross-sectional, and one was a cohort, giving a total of 3,460 participants. All studies presented a low risk of bias and reported an association between neurodegenerative disease and periodontitis. The articles showed that the groups with the two concomitant diseases had higher inflammatory markers levels, IgG levels of periodontal bacteria, and/or clinical parameters of periodontitis compared with the isolated conditions. However, the heterogeneity of the studies taken together hindered the accuracy of the evidence and also made impossible the merging of data. Also, it should be highlighted that no cohort study was retrieved regarding the association between periodontal disease and neurodegenerative diseases; therefore, causality cannot be claimed.
Although all the included studies in this review reported an association between neurodegenerative diseases and periodontitis, the level of evidence was classified to be very low, which suggests a cautious interpretation of the results.