Changes in Nighttime Sleep Duration and Their Association With Cognitive Decline and Dementia Risk

This study investigates changes in nighttime sleep duration in relation to cognitive decline and risk of incident dementia. A total of 3057 participants from the Swedish population study 'Good Aging in Skåne' (M_age = 68.4) with normal baseline sleep duration (6-8 h) were followed up to 20 years (M_years = 8.39). Self-reported change was defined as shortened or prolonged if participants lost or gained more than 1 h since their previous visit and sleep variability was defined as the SD of sleep duration across visits. Cognitive decline was assessed using an aggregated measure of global cognition. Linear mixed effects models examined the rate of decline across sleep change groups, adjusting for health-related factors, including time spent in bed without sleeping. Cox proportional hazard models estimated dementia risk. Longitudinal patterns of prolonged sleep (> 1 h increase) were associated with significant cognitive decline in fully adjusted models. Greater sleep variability was also associated with steeper cognitive decline. There was a 131% increased risk of dementia (HR = 2.31, 95% CI: I 1.77-3.03; p < 0.001) for prolonged sleep in comparison to stable sleep. Higher sleep variability was also associated with increased dementia risk (HR = 1.49, 95% CI: 1.70-1.89; p < 0.001). Shortened sleep was not found to be significantly associated with cognitive decline or dementia risk. These findings indicate that changes in sleep duration, particularly prolonged sleep and high variability, are associated with faster cognitive decline and incident dementia, and may serve as markers of future cognitive impairment.