Is short sleep bad for the brain? Brain structure and cognitive function in short sleepers

Abstract

Many sleep less than recommended without experiencing daytime tiredness. 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 needs and are more resistant to negative effects of sleep loss. We investigated this question using a combined cross-sectional and longitudinal sample of 47,029 participants (age 20-89 years) with measures of self-reported sleep, including 51,295 MRIs of the brain and cognitive tests. 701 participants who reported to sleep < 6 hours did not experience any daytime tiredness or sleep problems. These short sleepers showed on average larger regional brain volumes and only slightly lower general cognitive function compared to a group of 7-8 hours healthy sleepers (n = 3754). In contrast, short sleepers reporting excessive daytime tiredness and sleep problems (n = 1619) had smaller brain volumes and lower cognitive scores. Analyses using accelerometer-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 consequences for brain health, in line with a view on sleep need as individualized. Tiredness and sleep problems seem to be more relevant for neurocognitive function than sleep duration per se.