Summary: New evidence indicates that older adults who sleep more than eight hours per night or who go to bed unusually early may face a higher risk of developing dementia.
Source: Wiley
A recent study published in the Journal of the American Geriatrics Society reports that both the timing of sleep and the total time spent in bed are linked to the risk of dementia and to subsequent cognitive decline in older adults.
Researchers followed 1,982 older adults in rural western Shandong, China, who were free of dementia at the start of the study. Over an average follow-up period of 3.7 years, 97 participants were diagnosed with dementia.
Compared with those who slept seven to eight hours per night, people who reported sleeping more than eight hours had a 69% higher risk of developing dementia. In addition, going to bed before 9:00 p.m., compared with going to bed at 10:00 p.m. or later, was associated with roughly double the risk.
The authors note that these findings support closer cognitive monitoring of older adults who report unusually long time in bed or an early sleep schedule.
About this sleep and dementia research news
Author: Sara Henning-Stout
Source: Wiley
Contact: Sara Henning-Stout – Wiley
Image: The image is in the public domain
Original Research: Open access. “Associations of sleep timing and time in bed with dementia and cognitive decline among Chinese older adults: A cohort study” by Rui Liu MD et al., Journal of the American Geriatrics Society
Abstract
Background
The long-term relationships between when older adults sleep (sleep timing), how much time they spend in bed (time in bed, TIB), and later development of dementia or measurable cognitive decline are not well established. This study set out to clarify those associations using longitudinal data.
Methods
This population-based cohort study included 1,982 participants aged 60 years or older who were free of dementia at baseline and living in rural communities in western Shandong, China. Baseline assessments occurred in 2014 with follow-up examinations in 2018. Sleep characteristics were collected using standardized questionnaires, and cognitive function was assessed with the Mini-Mental State Examination (MMSE). Diagnoses of dementia followed DSM-IV criteria and NIA-AA criteria for Alzheimer disease when applicable. Statistical analyses included restricted cubic splines to explore dose–response patterns, Cox proportional-hazards models to estimate risk of incident dementia, and general linear models to examine change in cognitive scores.
Results
Over an average follow-up of 3.7 years, 97 participants received a dementia diagnosis, 68 of whom met criteria for Alzheimer disease. Analyses revealed non-linear, J-shaped relationships between sleep duration, time in bed, and rise time and dementia risk; mid-sleep time showed a reverse J-shaped pattern. When grouped into tertiles, participants reporting baseline sleep duration greater than eight hours had a multivariable-adjusted hazard ratio (HR) of 1.69 (95% CI, 1.01–2.83) for incident dementia compared with those sleeping seven to eight hours. Going to bed before 9:00 p.m. (versus 10:00 p.m. or later) was associated with an HR of 2.17 (95% CI, 1.22–3.87). Mid-sleep time before 1:00 a.m. (versus 1:00–1:30 a.m.) had an HR of 2.00 (95% CI, 1.23–3.24). Early bedtime and early mid-sleep time were also significantly associated with incident Alzheimer disease (HR range approximately 2.25–2.51).
Among participants who remained free of dementia at follow-up, several baseline sleep characteristics were linked with greater declines in MMSE scores: long time in bed, early bedtime and mid-sleep time, early and very late rise times. Changes over time toward longer time in bed or advancing bedtime and mid-sleep time were likewise associated with steeper cognitive decline. These patterns were most pronounced among men and among participants aged 60–74 years.
Conclusions
In this rural Chinese cohort, longer time in bed and earlier sleep timing were associated with higher risk of dementia and with greater cognitive decline in specific subgroups. The findings suggest that prolonged time in bed and markedly early sleep schedules in older adults could serve as clinical signals warranting closer cognitive monitoring and further assessment. While these associations do not prove causation, they highlight the importance of considering both sleep duration and sleep timing when evaluating risk factors for cognitive decline in older populations.
Clinicians and caregivers may consider documenting changes in sleep patterns—especially new or sustained increases in time spent in bed or consistently earlier bedtimes—as part of routine assessments for older adults. Additional research is needed to determine whether interventions aimed at normalizing sleep duration or timing can reduce dementia risk or slow cognitive decline.