Gut microbiota, sleep quality, and cognitive function in adults: A systematic review

Gut microbiota and sleep quality are reported to be important in physiological processes such as cognitive function. Yet, a systematic review examining the effect of both gut microbiota and sleep quality on cognitive function in adults is lacking. Therefore, this study aimed to examine the association between both sleep quality (efficiency, total sleep time) and gut microbiota composition in relation to cognitive function in adults.

This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched five online databases for original studies on human subjects that assessed cognitive function, sleep quality, and gut microbiota were eligible. The initial search resulted in 1646 titles/abstracts. Following the removal of duplicates and applying eligibility criteria, 21 studies (52% from China; 70.5% cross-sectional; 2,901patients) were included.

Sleep quality was assessed both using subjective and objective measures. Cognitive function was mostly evaluated with the Montreal Cognitive Assessment (38% of studies), while gut microbiota was predominantly analyzed using 16S rRNA sequencing (62%). Interestingly, no study was found that assessed gut microbiota, sleep, and cognitive function in individuals with cardiovascular disease. Observational findings consistently link objective sleep measures (efficiency, total sleep time) to greater gut microbial diversity in healthy adults, which correlates positively with better cognitive function. This relationship is mediated by microbial diversity relating significantly to inter-network functional connectivity in the brain. Conversely, pathological findings revealed that chronic insomnia is defined by a distinct microbiota dysbiosis (decreased Firmicutes/Actinobacteria and increased Bacteroidetes). Interventional studies showed that probiotic supplementation modulated gut composition, reduced physiological stress markers, and enhanced sleep quality and cognitive function in patients with cognitive impairment.

This systematic review confirms a complex and reciprocal relationship between sleep quality, gut microbial composition, and cognitive function in adults; therefore, optimal sleep and cognition are linked to greater gut microbial diversity. Higher microbial diversity correlates with superior objective sleep metrics and better cognitive function, mediated by enhanced inter-network functional connectivity in the brain. No studies assessed this triad (sleep, microbiota, and cognitive function) in individuals with cardiovascular diseases, marking a significant research gap.