Sleep Characteristics And Cognitive Function In Older Adults Without Dementia: The CABLE Study

Objective:Sleep is particularly important for brain health.During sleep,the brain can remove metabolic waste and promote learning and memory.Sleep disorders can impair these functions and bring many adverse consequences.In 2015,it was estimated that more than 47 million people worldwide had dementia,and by 2050,the number of cases of dementia is expected to triple to nearly 150 million,in part because of the increasing number of people over the age of 65.Alzheimer’s disease（AD）and vascular dementia are the two main types of dementia.According to the Global burden of Disease study,life loss caused by Alzheimer’s disease and other dementia increased by more than 50%from 1990to 2013.However,there is no effective strategy to treat dementia or predict its occurrence.Emerging evidence suggests that lifestyle factors,such as sleep disorders,may also increase the risk of dementia.In this study,based on a large number of elderly people with normal cognition,we explored the relationship between sleep characteristics（sleep quality and duration）and cognition,revealed the effect of sleep characteristics on AD markers in cerebrospinal fluid,and further looked for the possible mechanism of sleep affecting cognition,which is beneficial to the early prevention of dementia.Methods:A total of 974 participants who had measurements of cerebrospinal fluid（CSF）Aβ,P-tau,total Tau proteins,cognitive function,and sleep characteristics were included from the Chinese Alzheimer’s Biomarker and Lifestyle（CABLE）study.Linear regression analyses were utilized to explore the associations of sleep characteristics with cognition.Non-linear regression analyses were utilized to explore the associations of sleep habits with cognition.Causal mediation analyses were conducted to explore the mediation effects of AD pathologies on cognition.Results:The results of multiple linear regression showed a significant negative correlation between the PSQI total score and Mo CA score（P=0.0176）in participants with normal cognition.Among the seven factors of the PSQI,higher scores for sleep onset latency（P=0.0054）and sleep efficiency（P=0.0273）were associated with lower Mo CA scores.Habitual napping behavior in the elderly was associated with lower Mo CA scores（P=0.0045）,and elderly individuals who napped for longer than 0.5 hours had lower Mo CA scores compared to those who did not nap.U-shaped associations were observed between sleep habits（bedtime and nocturnal sleep duration）and cognition.Both insufficient and excessive sleep duration were associated with poorer cognitive function and higher levels of AD pathology.A causal mediation analysis indicated that P-tau/Aβ₄₂ mediated the association of sleep duration with cognition.Conclusion:These findings suggest that sleep characteristics are related to cognitive function,particularly sleep onset latency and sleep efficiency.Longer sleep onset latency and poorer sleep efficiency are associated with worse cognitive performance.Sleep habits,such as duration and timing of sleep,show a nonlinear relationship with cognitive function and CSF biomarkers.AD core pathology may partially mediate the effect of sleep time on cognitive impairment.Studies indicate a close association between sleep and cognitive function,and sleep may serve as a modifiable risk factor for dementia in early prevention,but longitudinal research is needed to further explore the relationship between sleep and cognition and the underlying mechanisms involved.