The impact of sleep components, quality and patterns on glymphatic system functioning in healthy adults: A systematic review

Objective: The glymphatic system is thought to be responsible for waste clearance in the brain. As it is primarily active during sleep, different components of sleep, subjective sleep quality, and sleep patterns may contribute to glymphatic functioning. This systematic review aimed at exploring the effect of sleep components, sleep quality, and sleep patterns on outcomes associated with the glymphatic system in healthy adults.Methods: PubMed (R), Scopus, and Web of Science were searched for studies published in English until December 2021. Articles subjectively or objectively investigating sleep components (total sleep time, time in bed, sleep efficiency, sleep onset latency, wake-up after sleep onset, sleep stage, awakenings), sleep quality, or sleep pattern in healthy individuals, on outcomes associated with glymphatic system (levels of amyloid-fl, tau, a-synuclein; cerebrospinal fluid, perivascular spaces; apolipoprotein E) were selected.Results: Out of 8359 records screened, 51 studies were included. Overall, contradictory findings were observed according to different sleep assessment method. The most frequently assessed sleep parame-ters were total sleep time, sleep quality, and sleep efficiency. No association was found between sleep efficiency and amyloid-fl, and between slow-wave activity and tau. Most of the studies did not find any correlation between total sleep time and amyloid-fl nor tau level. Opposing results correlated sleep quality with amyloid-fl and tau.Conclusions: This review highlighted inconsistent results across the studies; as such, the specific asso-ciation between the glymphatic system and sleep parameters in healthy adults remains poorly under-stood. Due to the heterogeneity of sleep assessment methods and the self-reported data representing the majority of the observations, future studies with universal study design and sleep methodology in healthy individuals are advocated.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This systematic review explores the impact of sleep components, sleep quality, and sleep patterns on outcomes associated with the glymphatic system in healthy adults. The findings reveal contradictory results based on different sleep assessment methods, indicating a lack of understanding regarding the specific association between sleep parameters and the glymphatic system in healthy adults.