Objectives Inadequate sleep increases the risk for age-related cognitive decline and recent work suggests a possible role of the gut microbiota in this phenomenon. Partial sleep deprivation alters the human gut microbiome, and its composition is associated with cognitive flexibility in animal models. Given these findings, we examined the possible relationship among the gut microbiome, sleep quality, and cognitive flexibility in a sample of healthy older adults. Methods Thirty-seven participants

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... (age 64.59 ± 7.54 years) provided a stool sample for gut microbial sequencing and completed the Pittsburgh Sleep Quality Index and Stroop Color Word Test as part of a larger project. Results Better sleep quality was associated with better Stroop performance and higher proportions of the gut microbial phyla Verrucomicrobia and Lentisphaerae. Stroop Word and Color-Word performance correlated with higher proportions of Verrucomicrobia and Lentisphaerae. Partial correlations suggested that the relationship between Lentisphaerae and Stroop Color-Word performance was better accounted for by sleep quality; sleep quality remained a significant predictor of Color-Word performance, independent of the Lentisphaerae proportion, while the relationship between Lentisphaerae and Stroop performance was non-significant. Verrucomicrobia and sleep quality were not associated with Stroop Word performance independent of one another. Conclusions The current findings suggest a possible relationship among sleep quality, composition of the gut microbiome, and cognitive flexibility in healthy older adults. Prospective and experimental studies are needed to confirm these findings and determine whether improving microbiome health may buffer against sleep-related cognitive decline in older adults.