Previous research has found that partial sleep deprivation alters the human gut microbiome. Besides this, data broadly suggest sleep and cognitive functioning are related in older age. However, there is no data regarding the involvement of the gut microbiome in the cognitive dysfunction associated with chronically poor sleep.
A recent study, led by Dr. John Gunstad from the Department of Psychological Sciences at Kent State University (Kent, USA), has found that there is a relationship between sleep habits, gut microbiome composition and cognitive flexibility in healthy older adults.
The researchers enrolled 37 healthy participants (aged 50 to 85 years) that provided a stool sample for gut microbiome sequencing and completed the Pittsburgh Sleep Quality Index-a measure of sleep quality, with higher scores indicating poorer sleep quality-as well as the Stroop Colour Word Test, which assesses cognitive flexibility when participants (1) read aloud colour words (‘Stroop Word’), (2) identify the corresponding ink colour of rows (‘Stroop Colour’) and finally (3) identify the ink colour of incongruent colour words; faster is better on this test, with higher scores indicating better outcomes. Participants also filled out a medical questionnaire on their current medical conditions, and the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk Food Frequency Questionnaire to assess habitual food intake over a 30-day period. Exclusion criteria were: history of neurological, developmental or severe psychiatric disorder, antibiotic or probiotic use within 30 days of study participation, history of significant gastrointestinal disorder or surgery, history of alcohol or illicit drug dependence, and history of severe heart, kidney or liver diseases.
Better sleep quality was related to better cognitive flexibility and higher proportions of the gut microbial phyla Verrucomicrobia and Lentisphaerae. Verrucomicrobia showed a positive association with Stroop Word performance, whereas Lentisphaerae showed a no significant association. Hypertension and carbohydrate intake were considered as covariates in all analyses due to their association with Stroop Colour Word Test scores. These data show that gut microbiota composition is associated with both sleep quality and cognitive flexibility in healthy older adults.
Partial correlations that examined whether gut microbiota composition was associated with Stroop Colour Word Test performance independent of sleep found that sleep quality and Verrucomicrobia were not independently associated with cognitive flexibility, whereas poorer sleep quality was associated with poorer cognitive flexibility independent of Lentisphaerae. Diet composition and other factors (e.g., systemic inflammation, physical activity, etc.) could possibly explain the relationship between sleep quality, cognitive flexibility and gut microbiome composition, though they were not taken into account in this study. These results show that an altered gut microbiota composition could mediate the relationship between poor sleep and cognitive function in healthy older adults.
In conclusion, gut microbiome shifts could be one mechanism involved in how poor sleep and lower cognitive flexibility are linked in older adults. According to the authors: “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”.
Anderson JR, Carroll I, Azcarate-Peril MA, et al. A preliminary examination of gut microbiota, sleep, and cognitive flexibility in healthy older adults. Sleep Med. 2017; doi: 10.1016/j.sleep.2017.07.018.