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Early Gut Microbiome Alterations in Mild Cognitive Impairment Reflect Changes in Alzheimer Disease

Emilia Brandt1,2, Anne Koivisto2,3,4, Pedro Pereira5,6,7

  • 1Institute of Clinical Medicine, School of Medicine, University of Eastern Finland, Kuopio, Finland.

Alzheimer Disease and Associated Disorders
|June 2, 2026
PubMed
Abstract

Insights

Gut microbiome changes linked to Alzheimer disease (AD) are already present in mild cognitive impairment (MCI). These alterations in gut bacteria may serve as early, noninvasive biomarkers for AD detection.

Area of Science:

  • Neuroscience
  • Microbiology
  • Gastroenterology

Background:

  • The gut-brain axis and its connection to neurodegenerative diseases like Alzheimer disease (AD) are increasingly recognized.
  • It is not yet understood if gut microbiome alterations are present during early stages of cognitive decline.

Purpose of the Study:

  • To investigate if gut microbiome alterations characteristic of AD are detectable in individuals with mild cognitive impairment (MCI).
  • To determine if these microbiome changes follow a consistent pattern across the spectrum of cognitive decline, from normal cognition to MCI and AD.

Main Methods:

  • A case-control study involving 78 participants: 37 cognitively healthy, 20 with MCI, and 21 with mild AD.
  • Cognitive function was assessed using the CERAD neuropsychological battery, and disease severity by the Clinical Dementia Rating.
  • Fecal samples were analyzed using 16S rRNA gene amplicon sequencing after collecting dietary data.

Main Results:

  • Sixteen bacterial genera were found to be associated with cognitive status.
  • Genera like Lacticaseibacillus, Raoultella, and Buttiauxella were decreased in AD, with similar reductions observed in MCI.
  • Anaerovorax and an unclassified Comamonadaceae genus were increased in AD, with trends consistent across the cognitive continuum.

Conclusions:

  • Gut microbiome alterations associated with AD are present even in early cognitive decline, including MCI.
  • The observed changes in gut bacteria follow a similar pattern from normal cognition through MCI to AD.
  • Microbiome profiles show potential as early, noninvasive biomarkers for AD.
Keywords:
Alzheimer disease (AD)biomarkerdementiagut microbiome (GM)mild cognitive impairment (MCI)

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