How much sleep was linked to the highest cognitive performance?

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Sleep is essential for life and daily cognitive processes, but how much is needed for optimal brain health as people age remains unclear. Poor memory and increased dementia risk have been associated with extremes of sleep quantity and disruptions in other sleep characteristics.

Researchers examined UK Biobank sleep and cognitive data from 479,420 healthy middle-to-late-life individuals aged 38–73, and assessed the relationship with brain structure in a subgroup of 37,553. Seven hours of sleep per day was associated with the highest cognitive performance, which decreased for every hour below or above that duration. This quadratic relationship remained present in older individuals over 60 years old (N = 212,006).

People who slept six to eight hours had significantly greater grey matter volume in 46 of 139 brain regions, including the orbitofrontal cortex, hippocampi, precentral gyrus, right frontal pole and cerebellar subfields. Several regions showed a quadratic relationship between sleep duration and volume, while others were smaller only in people who slept longer. The findings highlight relationships between sleep duration, a modifiable lifestyle factor, and cognition, as well as a widespread association between sleep and structural brain health.