Those who slept more than 10 hours or less than 4 hours per night declined faster than those who slept about 7 hours per night.
While there is a believed link between sleep duration and the trajectory of cognitive decline, it has not been extensively studied in the past.
A team, led by Yanjun Ma, BA, Peking University Clinical Research Institute, Peking University First Hospital, investigated the link between sleep duration and cognitive decline in geriatric individuals from a pooled analysis of a pair of nationally representative aging cohorts in China and the UK.
In the cohort, the investigators used data from waves 4-8 (2008-2009 to 2016-2017) in the English Longitudinal Study of Ageing and waves 1-3 (2011-2015) in the China Health and Retirement Longitudinal Study in a population-based setting.
There was a total of 28,756 participants in the 2 randomly enrolled cohorts, each of which was either living in England and at least 50 years or living in China and at least 45 years old.
Each participant self-reported sleep duration per night in face-to-face interviews.
The investigators sought main outcomes of global cognitive z scores, 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.
The team analyzed the from 20,065 total patients, 9254 from the English Longitudinal Study of Ageing with a mean age of 64.6 years old and 10,811 from the China Health and Retirement Longitudinal Study with a mean age of 57.8 years old.
In the English Longitudinal Study of Ageing the medial follow-up was 8 years and in the China Health and Retirement Longitudinal Study the mean follow-up was 4 years.
During the 100,000 person-years of follow-up, the global cognitive z scores in individuals with 4 hours or less (pooled β = −0.022; 95% CI, −0.035 to −0.009 SD per year; P = 0.001) and 10 hours or more (pooled β = −0.033; 95% CI, −0.054 to −0.011 SD per year; P = 0 .003) of sleep per night declined faster than in the reference group of 7 hours per night after adjusting for a number of covariates.
The investigators also observed an inverted U-shaped association between sleep duration and global cognitive decline.
“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, the authors wrote. “Future studies are needed to examine the mechanisms of the association between sleep duration and cognitive decline.”
Previously, researchers have reported a strong association between sleep and cognitive function in older adults and while a number of cohort studies have examined whether baseline sleep duration was linked to cognitive decline and incident dementia, the results have been inconsistent.
The study, “Association Between Sleep Duration and Cognitive Decline,” was published online in JAMA Network Open.