Andrea Herrera
Table of Contents
Why should we care about the microbiota when we think about brain diseases like Parkinson’s disease and dementia? Why do we ask for a stool sample at the CCBP study? The microbiota — the community of bacteria, viruses and other microbes living in our gut — interacts continuously with our immune system, metabolism, and nervous system. Studying microbiota in Parkinson’s research and dementia research could change how we diagnose, monitor, and even treat neurodegeneration.
This blog explains what the microbiota is, how gut bacteria and the gut-brain axis are linked to Parkinson’s disease and dementia, what research has already shown, and what still needs to be learned.
Understanding Microbiota
The human microbiota refers to the trillions of microorganisms that live on and inside the body. When people talk about the microbiota in health research, they are usually referring to gut bacteria, which make up the largest and most studied microbial community.
These gut microbes are not passive passengers. They help:
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Digest complex foods and fiber
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Produce vitamins and bioactive compounds
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Train and regulate the immune system
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Generate metabolites that travel through the bloodstream and reach the brain
What Is the Gut–Brain Axis?
The gut–brain axis is a two-way communication system linking the gastrointestinal tract and the brain. It includes:
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Neural pathways (such as the vagus nerve)
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Immune signaling
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Hormones and microbial metabolites
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When the microbiota is balanced, it supports healthy immune responses and brain function. When it becomes altered—a state known as dysbiosis—it may promote inflammation, disrupt the blood–brain barrier, and interfere with neuronal signaling. In simple terms, gut health and brain health are deeply connected
Biological Mechanisms Linking Microbiota to Brain Disease
Microbiota research suggests several interconnected pathways through which gut bacteria may influence Parkinson’s disease and dementia:
- Immune activation: dysbiotic microbiota can increase peripheral inflammation, affecting brain immune cells (microglia) and altering their clearance of toxic proteins.
- Metabolites: bacterial products such as short-chain fatty acids and lipopolysaccharide can influence neuronal signalling, barrier integrity, and inflammation.
- Neural routes: signals via the vagus nerve could carry microbial effects from the gut to brain regions affected in Parkinson’s and dementia.
The Role of Microbiota in Parkinson's Disease and Dementia
Microbiota in Parkinson's disease
Multiple studies have shown that people with Parkinson’s disease have different gut microbiota profiles compared with healthy individuals. These differences have been associated with:
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Motor symptom severity
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Non-motor symptoms
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Neuroinflammation
In animal models, microbiota research has gone even further. Experiments have shown that transferring gut bacteria from animals with Parkinson-like pathology to healthy animals can induce motor and inflammatory changes. These findings suggest that gut bacteria may not just reflect disease—but may actively modify disease processes.
Microbiota in dementia
In dementia research, including studies of Alzheimer’s disease, researchers have found different microbial signatures in people with cognitive impairment. These microbial changes may influence dementia through several mechanisms:
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Promoting chronic inflammation
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Affecting the production and clearance of amyloid and tau proteins
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Altering neurotransmitter precursors important for cognition
Some gut bacteria produce metabolites that support brain health, while others may generate pro-inflammatory molecules. Understanding this balance is essential for unraveling how the microbiota contributes to cognitive decline and neurodegeneration.
Research Gaps in Microbiota Studies
Despite several studies showing a correlation, we don’t know if microbial changes are the cause or the consequence of Parkinson’s or Alzheimer’s. How can we be sure? We need a study that can compare healthy and PD or dementia patients, including their diets, medications, ages, and geographic locations. After a genetic analysis of the microbiome, called metagenomics, and studying which microbial metabolites are protective versus harmful, we can better understand the potential risk.
Critical unanswered questions include:
- Which specific microbes or microbial communities consistently predict disease progression?
- How do common treatments (like antibiotics or L-DOPA) change microbiota and patient outcomes?
- Can modifying microbiota slow or prevent neurodegeneration in humans?
These gaps are addressed in the CCBP study, which is a larger longitudinal study that uses standardised methods for sampling and analysis and employs multi-omics approaches combining genetics, metabolomics, and immune profiling.
The Benefits of Stool Sample Analysis in Parkinson's and Dementia Research
Stool samples offer a practical, noninvasive window into the gut microbiota. Analyzing stool can reveal which bacteria are present, what genes they carry, and what metabolites they produce. For Parkinson’s and dementia research, stool-based biomarkers could help in several ways: early detection, tracking disease progression, predicting response to therapy, and guiding personalized interventions.
Can stool samples be used as biomarkers? Yes, some examples:
- Screening: Biomarkers could be found in stool samples to help identify individuals at higher risk for Parkinson’s or dementia
- Monitoring: Different samples can help to determine if the risk has decreased
- Dietary intervention: Due to the microbiome, interventions could change according to probiotic, dietary, or microbiota-transfer strategies. It may be a potential treatment for reducing inflammation and supporting brain health.
To be able to use biomarkers from stool samples, we require a study able to find potential biomarkers – one of our goals in the CCBP study, validated in the lab and have clinical trials that demonstrate that microbiota-based interventions work.
Conclusion
Research into the microbiota and the gut-brain axis is reshaping how scientists think about Parkinson’s disease and dementia. While clear mechanistic links have been established in animal models and consistent microbial differences have been observed in people, more work is needed to prove causality and to translate findings into clinically useful tools.
Studying stool samples offers a practical path forward for biomarker discovery, disease monitoring, and personalised therapies.
FAQs
- Can gut microbiota cause Parkinson’s disease or dementia?
Current evidence suggests gut microbiota may influence the risk and progression of Parkinson’s disease and some types of dementia. Still, definitive proof that they cause these diseases in humans is not yet established.
In humans, observed microbial changes could be cause, consequence, or both. Long-term studies that follow people before symptoms appear are needed to clarify causal relationships.
- What is a stool biomarker, and how reliable is it?
A stool biomarker is a measurable feature in faeces that reflects a biological process, such as the presence of certain bacteria, genes, or metabolites.
- Could changing my diet or taking probiotics prevent neurodegeneration?
Diet and probiotics can alter the microbiota and influence factors like inflammation and metabolism. Some small studies suggest possible benefits, but there is not yet strong clinical evidence that these changes prevent Parkinson’s disease or dementia in humans.
- How do medications affect the microbiota in patients with Parkinson’s?
Many medications, including antibiotics and Parkinson’s treatments such as L-DOPA, can alter gut microbiota composition. These changes may affect drug absorption, side effects, and disease-related symptoms such as constipation.
- What are the next steps in microbiota research for brain diseases?
The following steps are collecting stool samples, understanding and integrating microbiome genetic and metabolomic data, and conducting clinical trials testing microbiota-targeted interventions.
References
- Sampson TR, Debelius JW, Thron T, et al. Gut microbiota regulate motor deficits and neuroinflammation in a model of Parkinson’s disease. Cell. 2016.
- Scheperjans F, Aho V, Pereira PA, et al. Gut microbiota are related to Parkinson’s disease and clinical phenotype. Movement Disorders. 2015.
- Mulak A, Bonaz B. Brain-gut-microbiota axis in Parkinson’s disease. World Journal of Gastroenterology. 2015.
- Sharon G, Sampson TR, Geschwind DH, Mazmanian SK. The central nervous system and the gut microbiome. Cell. 2016.
- Vogt NM, Kerby RL, Dill-McFarland KA, et al. Gut microbiome alterations in Alzheimer’s disease. Scientific Reports. 2017.
- Cattaneo A, Cattane N, Galluzzi S, et al. Association of brain amyloidosis with pro-inflammatory gut bacterial taxa and peripheral inflammation markers in cognitively impaired elderly. Neurobiology of Aging. 2017.
- Erny D, Hrabe de Angelis AL, Jaitin D, et al. Host microbiota constantly control maturation and function of microglia in the CNS. Nature Neuroscience. 2015.
- Fung TC, Olson CA, Hsiao EY. Interactions between the microbiota, immune and nervous systems. Nature Neuroscience. 2017.
- Needham BD, Trent MS. Fortifying the fortress: the role of the microbiota in modulating the blood–brain barrier. Journal of Clinical Investigation. 2019.