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Published on: January 11, 2020
Gut Microbiota, Mild Cognitive Impairment and Dementia: A Systematic Review
Claudio Tana1, Samanta Moffa2, Marco Tana3
1Internal Medicine Unit, Eastern Hospital, ASL Taranto, 74121 Taranto, Italy.
Background:
Alterations of the gut microbiota have been increasingly implicated in the pathogenesis of dementia through mechanisms involving systemic inflammation, immune dysregulation, and gut-brain axis disruption. Clinical evidence, however, remains fragmented.
Objectives:
This systematic review aimed to characterize gut microbiota profiles in individuals with mild cognitive impairment (MCI) or Alzheimer's dementia (AD), explore mechanistic associations with neurodegeneration, and evaluate the impact of microbiota-targeted interventions on cognitive outcomes.
Methods:
Following PRISMA 2020 guidelines and a registered protocol (PROSPERO CRD420251074832), PubMed/Medline was searched through May 2025. Eligible studies included randomized controlled trials (RCTs) and cohort and case-control studies assessing microbiota composition or interventions in participants with MCI or AD.
Results:
Twenty-one studies were included (1 RCT, 20 observational; sample size 22-302). Most used 16S rRNA sequencing; one used shotgun metagenomics. Across cohorts, MCI and AD patients consistently showed reduced short-chain fatty acid-producing bacteria (Faecalibacterium, Ruminococcaceae, Lachnospiraceae) and increased pro-inflammatory taxa (Escherichia/Shigella, Enterobacteriaceae, Bacteroides). Several studies reported reduced microbial diversity. Specific taxa, including Akkermansia muciniphila and Faecalibacterium, were associated with amyloid burden, hippocampal atrophy, and cognitive decline. Environmental and dietary factors influenced microbial composition and cognition. The RCT reported that probiotic supplementation improved inflammatory markers and BDNF levels, although changes in microbiota composition were inconsistent.
Conclusions:
Gut dysbiosis is strongly associated with cognitive impairment and markers of neurodegeneration. Modulation of the microbiota through diet and probiotics emerges as a promising avenue for dementia prevention and management, though robust longitudinal and interventional studies are needed to confirm causality and therapeutic efficacy.
Insights
Gut dysbiosis, characterized by reduced beneficial bacteria and increased harmful bacteria, is linked to cognitive decline and neurodegeneration. Microbiota modulation via diet and probiotics shows promise for dementia prevention and management.
Area of Science:
- Neuroscience
- Microbiology
- Gastroenterology
Background:
- Gut microbiota alterations are increasingly linked to dementia pathogenesis via inflammation and gut-brain axis disruption.
- Clinical evidence supporting this connection remains fragmented, necessitating further investigation.
- Systemic inflammation, immune dysregulation, and gut-brain axis disruption are key proposed mechanisms.
Purpose of the Study:
- To characterize gut microbiota profiles in mild cognitive impairment (MCI) and Alzheimer's dementia (AD).
- To explore mechanistic associations between gut microbiota and neurodegeneration.
- To evaluate the impact of microbiota-targeted interventions on cognitive outcomes.
Main Methods:
- A systematic review following PRISMA 2020 guidelines.
- Searched PubMed/Medline through May 2025.
- Included randomized controlled trials (RCTs), cohort, and case-control studies on microbiota in MCI or AD patients.
Main Results:
- Twenty-one studies (1 RCT, 20 observational) were included.
- MCI and AD patients showed reduced short-chain fatty acid-producing bacteria and increased pro-inflammatory taxa, with reduced microbial diversity.
- Specific taxa were associated with amyloid burden, hippocampal atrophy, and cognitive decline; probiotic supplementation showed potential benefits for inflammatory markers.
Conclusions:
- Gut dysbiosis is strongly associated with cognitive impairment and neurodegeneration markers.
- Microbiota modulation through diet and probiotics is a promising strategy for dementia prevention and management.
- Further robust longitudinal and interventional studies are required to confirm causality and efficacy.
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