Does sleep duration affect the brain?

There is concern about whether insufficient sleep is a negative factor for physical, mental, and cognitive health in society. Some have argued that our modern society is suffering from an 'insomnia epidemic.' After reviewing the research in the field, we have concluded that there is no convincing evidence showing that short sleep causes poorer brain health. The ambitious goal of this project is to directly test the relationship between sleep duration and brain health and to investigate to what extent such a relationship is causal. We will establish a database with more than 70,000 MRI brain images from over 60,000 participants. This will include longitudinal studies from 5,000 participants who have been followed for up to over 10 years. We will use new approaches to brain imaging analysis, integrating several structural, functional, and microstructural measurements in the same analyses, which we hope will yield biologically more meaningful variables and greater sensitivity. Sleep will be measured in a naturalistic setting, combining self-reported measures with objective sleep recordings. To examine causality, we will look at genetic pleiotropy between sleep duration and brain measures and conduct Mendelian randomization analyses, where genetic variation is used as a natural experiment to investigate causal relationships. This will be combined with methods for causal inference for longitudinal data. Here, we will test whether changes in sleep duration over time follow or precede changes in the brain and examine the relationship with physical and mental health. The analyses will be enriched with 200 participants who, in addition to MRI, will undergo repeated polysomnography examinations, allowing for direct study of sleep architecture. So far in the project, we have calculated the sleep duration associated with 'optimal' brain health as measured by MRI. On average, people who sleep 6.5 hours have the best results on MRI scans, a figure lower than international sleep recommendations but consistent with findings across various areas, such as cognitive function, mortality, and cardiovascular health. Furthermore, we have found that people who consistently sleep less than 6 hours do not have worse brain health than others, as long as they do not have specific sleep problems or experience significant daytime sleepiness. The project has also contributed theoretically to international discussions on sleep, cognitive function, and brain health.

There is a worry in society that too little sleep is a pervasive negative factor for somatic, mental and cognitive health, with suggestions that we are suffering an ‘epidemic of sleeplessness'. Reviewing the research on the relationship between sleep duration and the brain, we came to the conclusion that there is as of yet no conclusive evidence showing that short sleep causes poorer brain health. Thus, the ambitious objective of BrainSleep is directly to test the relationship between sleep duration and brain health and to decide to what degree such a relationship may be causal. We will create a database of > 70.000 structural and functional MRIs of the brain from > 60.000 participants, including 5000 longitudinal examinations covering intervals up more than a decade. BrainSleep will use novel approaches to MRI analyses, integrating multiple structural, microstructural and functional measures in the same analyses, yielding biologically more meaningful variables and higher sensitivity. Sleep will be measured in a natural setting, combining standardized self-report measures with objective sleep registrations. To address the problem of causality, we will assess genetic pleiotropy between sleep duration and brain measures and run Mendelian randomization analyses where genetic variation is used as a natural experiment to investigate the causal relations. This will be combined with causal inference methods applied to longitudinal data, where we will test whether changes in sleep duration over time precede or follow changes in brain features, and by scrutinizing effects of a range of somatic and mental health variables which may cause spurious relationships between sleep duration and brain health. The analyses will be enriched by a sample of 200 participants who in addition to structural and functional MRI will undergo repeated polysomnography, allowing us directly to study sleep architecture underlying macro-measures of sleep in the large-scale analyses.