| Summary: | Many sleep less than recommended without experiencing daytime sleepiness. According to
prevailing views, short sleep increases risk of lower brain health and cognitive function. Chronic mild
sleep deprivation could cause undetected sleep debt, negatively affecting cognitive function and
brain health. However, it is possible that some have less sleep need and are more resistant to
negative effects of sleep loss. We investigated this using a cross-sectional and longitudinal sample of
47,029 participants of both sexes (20-89 years) from the Lifebrain consortium, Human Connectome
project and UK Biobank, with measures of self-reported sleep, including 51,295 MRIs of the brain and
cognitive tests. 740 participants who reported to sleep < 6 hours did not experience daytime
sleepiness or sleep problems/ disturbances interfering with falling or staying asleep. These short
sleepers showed significantly larger regional brain volumes than both short sleepers with daytime
sleepiness and sleep problems (n = 1742) and participants sleeping the recommended 7-8 hours (n =
3886). However, both groups of short sleepers showed slightly lower general cognitive function, 0.16
and 0.19 standard deviations, respectively. Analyses using acelerometer-estimated sleep duration
confirmed the findings, and the associations remained after controlling for body mass index,
depression symptoms, income and education. The results suggest that some people can cope with
less sleep without obvious negative associations with brain morphometry, and that sleepiness and
sleep problems may be more related to brain structural differences than duration. However, the
slightly lower performance on tests of general cognitive abilities warrants closer examination in
natural settings
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