Association Between Sleep Duration and Cognitive Decline

This pooled cohort study investigates the association between sleep duration and cognitive decline in a combined analysis of 2 nationally representative aging cohorts. Importance An association between sleep duration and the trajectory of cognitive decline has not been conclusively demonstrated. Objective To investigate the association between sleep duration and cognitive decline by a pooled analysis of 2 nationally representative aging cohorts. Design, Setting, and Participants A pooled cohort study using data from waves 4 to 8 (2008-2009 to 2016-2017) in the English Longitudinal Study of Ageing and waves 1 to 3 (2011 to 2015) in the China Health and Retirement Longitudinal Study in a population-based setting. Participants were 2 randomly enrolled cohorts comprising 28 756 individuals living in England who were 50 years or older and those living in China who were 45 years or older. Exposure Self-reported sleep duration per night according to face-to-face interviews. Main Outcomes and Measures Global cognitive z scores were calculated according to immediate and delayed recall test, an animal fluency test, the serial sevens test, an intersecting pentagon copying test, and a date orientation test. Results Data were analyzed from 20 065 participants, including 9254 from the English Longitudinal Study of Ageing (mean [SD] age, 64.6 [9.8] years; 55.9% [5174 of 9254] women; median follow-up duration, 8 [interquartile range, 6-8] years) and 10 811 from the China Health and Retirement Longitudinal Study (mean [SD] age, 57.8 [9.0] years; 50.2% [5425 of 10 811] men; median follow-up duration, 4 [interquartile range, 4-4] years). During 100 000 person-years of follow-up, global cognitive z scores in individuals with 4 hours or less (pooled beta = -0.022; 95% CI, -0.035 to -0.009 SD per year; P = .001) and 10 hours or more (pooled beta = -0.033; 95% CI, -0.054 to -0.011 SD per year; P = .003) of sleep per night declined faster than in the reference group (7 hours per night) after adjusting for a number of covariates. An inverted U-shaped association between sleep duration and global cognitive decline was also observed. Conclusions and Relevance In this pooled cohort study, an inverted U-shaped association between sleep duration and global cognitive decline was found, indicating that cognitive function should be monitored in individuals with insufficient (<= 4 hours per night) or excessive (>= 10 hours per night) sleep duration. Future studies are needed to examine the mechanisms of the association between sleep duration and cognitive decline. Question What is the association between sleep duration and cognitive decline in the general aging population? Findings During 100 000 person-years of follow-up in this pooled cohort study of 28 756 individuals, global cognitive function in individuals with extreme sleep duration (<= 4 or >= 10 hours per night) declined statistically significantly faster than in the reference group (7 hours per night) after adjusting for covariates. An inverted U-shaped association between sleep duration and global cognitive decline was also observed. Meaning The inverted U-shaped association indicates that cognitive function should be monitored in individuals with insufficient or excessive sleep duration.