Sleeping too little or too much, meaning no more than 4 hours per night or at least 10 hours per night, respectively, is associated with faster cognitive decline compared with sleeping approximately 7 hours per night, according to study results published in JAMA Network Open.
Study researchers from China sought to examine the relationship between sleep duration and cognitive decline. They achieved this by conducting an observational study, analyzing a pooled cohort of participants from waves 4 to 8 (2008-2009 to 2016-2017) of the English Longitudinal Study of Ageing and waves 1 to 3 (2011 to 2015) of the China Health and Retirement Longitudinal Study. In total, the pooled cohort included 9254 individuals from England who were at least 50 years of age (55.9% women; mean age, 64.6 years; median follow-up duration, 8 years) and 10,811 individuals living in China who were at least 45 years of age (50.2% men; mean age, 57.8 years; median follow-up duration, 4 years).
The investigators assessed face-to-face interview responses to obtain self-reported, per-night sleep duration information from participants. Sleep duration data were then correlated with global cognitive z scores, which were calculated based on the immediate and delayed recall test, animal fluency test, serial sevens test, an intersecting pentagon copying test, as well as a date orientation test.
Compared with a reference group of participants who slept for approximately 7 hours per night, global cognitive z scores declined significantly faster for those who slept no more than 4 hours per night (pooled β=-0.022; 95% CI, -0.035 to -0.009; P =.001) or at least 10 hours per night (pooled β=-0.033; 95% CI, -0.054 to -0.011; P =.003) in an analysis adjusted for age, body mass index, and other covariates. The investigators observed an inverted U-shaped association between sleep duration and global cognitive decline, in addition to memory in these participants.
Limitations of this study included its observational design, the reliance on self-reported data for the assessment of sleep duration, and the use of isolated tasks rather than more sensitive methods for the measurement of cognitive function.
The study researchers concluded that “the inverted U-shaped association indicates that cognitive function should be monitored in middle-aged and older individuals with insufficient or excessive sleep duration.”
Ma Y, Liang L, Zheng F, Shi L, Zhong B, Xie W. Association between sleep duration and cognitive decline. JAMA Netw Open. Published online September 21, 2020. doi:10.1001/jamanetworkopen.2020.13573