Everyone is aware of the damage that chronic consumption of alcohol causes. It’s been long known that over-imbibing can cause vitamin and mineral deficiencies, especially zinc, and it goes without saying how the liver suffers for irresponsible alcohol consumption. What about how alcohol affects our microbiome, the delicate ecosystem of bacteria within our bodies? A new study finds that binge drinking alters the bacteria population in our mouth to such an extent that it can be traced to the development of Alzheimer’s disease.
Researchers working with the Human Microbiome Project discovered pathways that are activated by changes in the oral microbiome caused by overconsumption of alcohol. These pathways activate signaling changes which alter the permeability of the blood brain barrier (BBB). The changes in the BBB have been found to be causative for the development of Alzheimer’s disease.
Why the Mouth is Vulnerable
The reason for such a huge change in the oral bacteria? It’s due to the acetaldehyde, the main metabolite of alcohol as it metabolized in the liver. In saliva, acetaldehyde is higher than in blood immediately after consuming alcohol; and 30 minutes later, the level of alcohol in the saliva is the same as the blood alcohol level. Acetaldehyde damages the tissues with which it comes into contact, damaging the oral cavity and mucousa which is a key factor in the changes of the oral microbiome.
Alcohol also causes changes in the salivary glands which change the pH level inside the mouth. Bacteria are very sensitive to pH levels, and they are easily influenced by changes in their environment, allowing some bacteria to flourish and others to diminish.
Gingivitis & Alzheimer's Disease
There is also a relationship between gum disease, the bacteria P. gingivalis (significant in chronic periodontitis), and Alzheimer’s disease. The P. gingivalis bacteria and other cavity-causing bacteria stimulate signaling pathways which releases cytokines. Eventually, these types of cascades also cause the blood brain barrier—which is normally highly selective to only allow certain types of molecules to pass through to the brain tissue—to weaken. With the blood brain barrier more permeable, the neurons are vulnerable to the passage of bacteria and toxins straight to neural tissue which should not be there.
The Blood Brain Barrier & Alzheimer's Disease
Alzheimer’s disease and other neurodegenerative diseases are closely linked to the brain blood barrier. Damage to this barrier is commonly found in autopsies of patients with Alzheimer’s disease. Alcohol increases the expression of a lipopolysaccharide; together, the presence of alcohol and lipopolysaccharide activate blood brain barrier-specific disruption. It is the weakened blood brain barrier which the authors of the study believe contributes to the amyloid cascade hypothesis, a series of events in which the body accumulates beta-amyloid faster than it can clear it. Beta amyloid and the formation of beta amyloid plaques are a hallmark characteristic of the neurodegeneration that accompanies Alzheimer’s disease.
In this study, the researchers also noted two specific genes that are linked between alcoholism and Alzheimer’s disease (APOA1 and PKR). Further research about this should prove very interesting as more investigation into this link is conducted.
Yussof, A., Yoon, P., Krkljes, C. et al. A meta-analysis of the effect of binge drinking on the oral microbiome and its relation to Alzheimer’s disease. Sci Rep 10, 19872 (2020). https://doi.org/10.1038/s41598-020-76784-x