Gut microbiome and Alzheimer’s disease
The fact that our health begins in the gut has been known for thousands of years. Today it is clear that our intestines are more than just a “digestive tube”, as this important organ fulfils a variety of other functions. For example, a disturbance of gut health is directly related to the development of chronic diseases.
The intestinal flora, i.e. the microbial colonization of the intestinal mucosa, plays a particularly important role in this process. The intestinal flora is also known as the ‘intestinal microbiota’. It is the most important part of our immune system and thus offers us effective protection against infection.
But what few people know is that a correctly composed intestinal flora is also essential for our brain health, as it is directly connected to our nervous system via the intestinal-brain axis. An imbalance in the intestinal flora can lead to devastating consequences for the nerve tissue and in the worst case can cause neurodegeneration and dementia.
Alterations in the composition of the gut microbiota, caused by dietary changes, antibiotic exposure, and infection lead to the loss of the physiologic balance, which is implicated in the development of several diseases in humans, including Alzheimer’s disease. Recent evidence points to a causative link between changes in the intestinal microbiota composition, along with inflammatory changes in brain tissue. Hence, gut microbes may alter the level of neurotransmitter-related metabolites, affecting gut-to-brain communication and/or altering brain function.
Many studies on animal models have provided strong evidence of the importance of microbiota in the pathology of Alzheimer’s disease. Interesting results have been obtained, for example, with mice reared without intestinal microbial colonization and therefore without intestinal microbiota. These ‘aseptic’ mice showed an increased permeability of the blood-brain barrier (BBB) compared to mice with normal intestinal flora. This means that pathogens and other harmful substances from which the brain with an intact BBB is normally protected, are now able to enter the brain tissue. This can lead to an inflammatory reaction in the central nervous system called neuroinflammation, which is directly linked to the development of Alzheimer’s disease (see section causes for further information).
Such results obtained in animal models have also been confirmed by clinical studies: For example, the intestinal microbiota of elderly people suffering from cognitive disorders was investigated, and an association between plaque deposits in the brain with the occurrence of pro-inflammatory intestinal bacteria and other inflammation markers could be shown.
In summary, all these results provide clear evidence that the effect of the intestinal microbiota on the development of the amyloid pathology may be significant and thus define its important role in the pathogenesis of Alzheimer’s disease.
But the good news is that our gut microbiota is a dynamically modifiable system that is very sensitive to lifestyle and ageing. With this knowledge, we can use a healthy lifestyle to positively influence our intestinal microbiota and develop practical recommendations for the prevention and treatment of Alzheimer’s disease.
Are you curious and would like to know more about this topic?
To support the project ‘Knowledge stops Dementia’ (https://kompetenz-statt-demenz.de/en/) the Academy of Human Medicine (AMM) has developed a fact sheet on dementia and intestinal health, which provides you with an evidence-based but compact overview of the above described relationships.
If you are interested in this fact sheet, it would be best to take part in the AMM’s current fundraising campaign for KSD.
And don’t forget: healthy gut, healthy brain!
We thank you in advance for your support!
Your KsD team
- Vogt NM, Kerby RL, Dill-McFarland KA, et al. Gut microbiome alterations in Alzheimer’s disease. Sci Rep. 2017;7(1):13537.
- Harach T, Marungruang N, et al. Reduction of Abeta amyloid pathology in APPPS1 transgenic mice in the absence of gut microbiota. Sci Rep. 2017 Feb 8;7:41802.
- Kowalski K, Mulak A. Brain-Gut-Microbiota Axis in Alzheimer’s Disease. J Neurogastroenterol Motil. 2019;25(1):48‐60.