The Interplay between Gut Microbiota and Cognitive Functioning in the Healthy Aging Population: A Systematic Review

Abstract

Background: The gut microbiota in healthy older individuals typically show a decrease in beneficial bacteria like Bifidobacterium and Lactobacillus, alongside an increase in pro-inflammatory microbes such as Enterobacteriaceae and Clostridia. These changes contrast with younger and middle-aged individuals and appear to correlate with cognitive status. Although there is extensive research on gut microbiota and cognitive functions in cognitively impaired elderly individuals, its impact on cognitively healthy elderly populations has not been extensively studied. Method: A PubMed, EBSCO, Web of Science, and Scopus literature search combined the terms (“human” OR “people” OR “individual*” OR “healthy” OR “neurologically healthy” AND (“older adults” OR “aging” OR “older” OR “senior*” OR “old” OR “elderly” OR “oldest”) AND (“gut microbiota*” OR “gut-microbiome” OR “gut microbiome composition” OR “gut microbiota composition” OR “gut-microbiome” OR “microbiome” OR “microbial diversity” OR “gut microbiome diversity” OR “gut microflora” OR “gut-brain axis” OR “dysbiosis” OR “gut bacteria” OR “gastrointestinal microbiota”) AND (“cognitive flexibility” OR “cognitive decline” OR “cognitive” OR “cognitive health” OR “cognition” OR “cognitive function” OR “cognitive performance”) to identify studies that examine the relationship between gut microbiota composition and cognitive functioning in healthy older adults. Results: A total of 6 eligible research articles from a possible 1752 published until March 2024 were identified and included. We categorized the included studies into two groups based on their focus: the taxonomic composition of gut microbiota and the alpha diversity, which is the variety of organisms within a sample. Additionally, two methods were identified for assessing cognition: neuropsychological tests and physiological measurements, notably electroencephalography (EEG). The studies show varying results regarding the abundance of specific bacterial taxa and their cognitive associations. Notably, the relationship between certain bacteria and cognition may vary when analyzed at different taxonomic levels, such as phylum versus family. Conclusions: Changes in gut microbiota composition in the elderly, even without a cognitive impairment diagnosis, could potentially serve as early biological markers for Alzheimer’s disease or other dementias before mild cognitive impairment appears.

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“…[ 33 ] Furthermore, emerging data have suggested changes in gut microbiota composition in predicting cognitive function later in life. [ 34 ] A biological link between gut and brain function – i.e. the gut-brain axis – has been previously reviewed [ 35 ] and has been implicated in the pathogenesis of neurodegenerative disorders such as Parkinson disease.…”