Health Shot: Linking the microbiome with dementia

Two new studies from this week show a growing consensus that the gut plays a role in neurodegenerative diseases

Illustration by Stephanie Davidson for Mood Health

Welcome to Health Shot, where we look at the newest research related to gut health, autoimmunity, chronic illness, stress, and the relationship between them. If you follow research related to these topics, you know that there’s a lot of it and it’s far from definitive.

While no individual study can provide definitive answers, taken together, we can start to see where the findings are headed, long before they make their way into medical practice. One of the goals of Health Shot is to identify and highlight these trends.

There is more and more research connecting the gut microbiome with neurodegenerative diseases like Parkinson’s, Alzheimers, ALS and MS. While five years ago this connection still sounded kind of far out to a layperson, recently it has become more of a scientific and popular consensus: there is some relationship between gut dysfunction and neurodegeneration, even if we still don’t know how it works or in which direction causality runs.

I keep an eye on this research, since multiple neurodegenerative diseases run in my family. These diseases are increasingly common—almost 10% of US adults over 65 have dementia, a term which includes Alzheimer’s and other forms of neurodegeneration. So a paradigm shift in how we think about these diseases, from the brain to the gut, could affect a lot of people.

I wanted to highlight two studies in this area that came out this week, which provide a good overview of the current state of our knowledge.

This Week’s New Studies:

1. The Role of Gut Microbiota in Neurodegenerative Diseases: Current Insights and Therapeutic Implications

Published October 28th, 2023 in Cureus

Key Takeaway

Studies to date have shown many pathways through which gut microbiota can impact brain health, with strong evidence that the gut microbiome impacts the trajectory of certain neurodegenerative diseases. Current research suggests future therapeutic paths that are exciting but which face significant challenges.

The Study

For this meta analysis, scientists reviewed 415 articles studying the connection between gut and neurodegenerative diseases like Parkinson’s, Alzheimers, MS, and ALS.

The reviewers found that there is strong evidence of a link between gut health and neaurodegenerative diseases. Some of the findings across the research include:

• The microbiome affects our immune responses and can trigger system-wide inflammation, affecting the brain

• The gut produces metabolites that may have an impact on brain health

• Gut barrier permeability is associated with the development of neurodegenerative diseases

• Accumulation of certain proteins linked to disease is associated with the presence of specific bacterial species in the gut

• People with Parkinson’s and Alzheimers have less microbial diversity and a different microbial makeup in the gut

• People with neurodegenerative diseases have drastically different levels of specific gut bacteria, including Firmicutes and Bacteroidetes

The researchers conclude that there are exciting therapeutic possibilities to explore based on the current research, including "psychobiotics," or bacteria that may have psychological advantages.

At the same time, the complexity of the microbiome and its interactions with the rest of our body systems, as well as the individual nature of these diseases make it challenging design experiments to run trials. The authors also raise questions of ethics, patient autonomy, access and regulation as we venture into projects to alter the microbiomne. Much of the existing research also uses mouse models, which may not translate into humans. While there’s a lot of promise here, the path ahead is long.

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2. Gastrointestinal Diseases, Genetic Risk, and Incident Dementia: A Prospective Cohort Study in 352,463 Middle-Aged Adults

Published October 31st, 2023 in the American Journal of Preventative Medicine

Key Takeway

People who have digestive system diseases such as IBS appear to be at a higher risk of dementia.

The Study

This study looked at records from over 350 thousand adults in the UK to see whether adults who had one of fourteen digestive disease were more likely to develop dementia. They found that eleven of the diseases correlated significantly with increased dementia risk.

The gut diseases more strongly associated with early-onset dementia were cirrhosis, irritable bowel syndrome, gastritis and duodenitis, gastroesophageal reflux disease, ulcerative colitis, gallbladder disease and peptic ulcer.

The authors suggest that, while the research can’t conclude causality, the findings suggest that there is a need for additional dementia prevention efforts among patients with gut diseases.

I’m curious…

What are your initial thoughts and feelings about these two studies? What else have you been reading about the link between dementia and the gut/microbiome?