The Role of Gut Microbiota in Brain Health: Connecting the Gut and the Mind

Approximately 70-80% of immune cells lead to changes in gut microbiota. Gut microbiota have been demonstrated to influence neurological diseases, including Alzheimer’s. The gut-brain axis is composed of both direct and indirect signaling pathways that connect the gut to the brain. Gut microbiota can metabolize, or process nutrients, leading to the release of small molecules to the gastrointestinal (GI) tract.2

Gut-brain connection through afferent fibers

Bacterial metabolites and amyloids, a protein that is prevalent in Alzheimer's disease, can trigger inflammation in the CNS, leading to degeneration. Additionally, gut microbiota can make protein clearance more difficult. Some studies suggest that buildup of amyloid-beta plaques occurs in the gut prior to the accumulation in the brain, found by autopsy reports. The buildup of proteins can increase neuroinflammation, and afferent fibers also play an important role. Afferent fibers are sensory neurons that have the ability to transmit information to the brain, changing levels of neurotransmitters.1

In one study, patients that were positive for amyloid demonstrated lower levels of specific bacterium compared to the control group, showing that gut microbiota does differ in Alzheimer’s patients.2 Prebiotics and probiotics have been utilized alone, and in combination, to show some improvement in Alzheimer's patients and other neurodegenerative diseases.

References

1. Bostanciklioğlu, M. (2019). The role of gut microbiota in pathogenesis of Alzheimer's disease. Journal of applied microbiology, 127(4), 954-967.

2. Molinero, N., Antón-Fernández, A., Hernández, F., Ávila, J., Bartolomé, B., & Moreno-Arribas, M. V. (2023). Gut microbiota, an additional hallmark of human aging and neurodegeneration. Neuroscience, 518, 141-161.