Abstract
Sleep is essential for life, including daily cognitive processes, yet the amount of sleep required for optimal brain health as we grow older is unclear. Poor memory and increased risk of dementia is associated with the extremes of sleep quantity and disruption of other sleep characteristics. We examined sleep and cognitive data from the UK Biobank (N = 479,420) in middle-to-late life healthy individuals (age 38–73 years) and the relationship with brain structure in a sub-group (N = 37,553). Seven hours of sleep per day was associated with the highest cognitive performance which decreased for every hour below and above this sleep duration. This quadratic relationship remained present in older individuals (>60 years, N = 212,006). Individuals who sleep between six-to-eight hours had significantly greater grey matter volume in 46 of 139 different brain regions including the orbitofrontal cortex, hippocampi, precentral gyrus, right frontal pole and cerebellar subfields. Several brain regions showed a quadratic relationship between sleep duration and volume while other regions were smaller only in individuals who slept longer. These findings highlight the important relationship between the modifiable lifestyle factor of sleep duration and cognition as well as a widespread association between sleep and structural brain health.
Highlights
Sleep is essential for life, including daily cognitive processes, yet the amount of sleep required for optimal brain health as we grow older is unclear
The results of this study show that the amount of time people sleep, an important and potentially modifiable lifestyle factor, is predictive of cognitive function across age in middle-to-late healthy individuals
Peak cognitive performance was associated with seven hours of overnight sleep in the sizeable cohort of the UK Biobank
Summary
Sleep is essential for life, including daily cognitive processes, yet the amount of sleep required for optimal brain health as we grow older is unclear. Seven hours of sleep per day was associated with the highest cognitive performance which decreased for every hour below and above this sleep duration This quadratic relationship remained present in older individuals (>60 years, N = 212,006). Several brain regions showed a quadratic relationship between sleep duration and volume while other regions were smaller only in individuals who slept longer These findings highlight the important relationship between the modifiable lifestyle factor of sleep duration and cognition as well as a widespread association between sleep and structural brain health. A further issue involves the classification of ‘short’ and ‘long’ sleep durations with studies choosing variable thresholds ranging from less than five to eight hours as being ‘short’ while other studies consider greater than seven to 10 h as ‘long’ sleep durations This block duration approach imposes a linear relationship between cognition and more or less sleep around a chosen cut-off. A recent longitudinal analysis of a 7,959 sub-cohort of the Whitehall study suggested that low sleep duration of six hours or less was associated with a higher dementia risk compared to sleeping seven hours, a long sleep duration of eight hours or more was not[16]
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