Sleep research in 2023: beyond the bare necessities

Abstract

In experimental models, the traditional approach to investigate sleep function is by depriving research animals of sleep.1 However, this approach might have confounding effects due to the stress induced by the procedure, potentially affecting the results.1 Generally, in old animals, the effects of ageing outweigh the effects of sleep deprivation. Sleep deprivation contributes to the accumulation of amyloid β and the release of tau, which are proteins associated with Alzheimer's disease.3 The glymphatic clearance of these proteins from the brain occurs during slow-wave sleep. Because slow-wave sleep changes with aging, investigating if changes in the percentage of sleep spent in slow-wave sleep are linked to risk of dementia later in life has become a topic of interest. 346 participants—with a mean age of 69 years—from the community-based Framingham Heart Study Offspring and Omni cohorts whose percentage of slow-wave sleep at baseline was comparable with that of healthy controls, were examined approximately every 4 years to analyse the decline in slow-wave sleep percentage.4 The investigators reported 52 cases of incident dementia, of which 44 were consistent with Alzheimer's disease dementia, over a mean follow-up of 12 years. Obstructive sleep apnoea is also relevant when considering the link between insomnia and increased risk of cardiovascular disease, heart failure, and mortality.5 Investigators assessed the association of three different insomnia presentations with subclinical myocardial injury, as measured by cardiac troponin T, in 2188 participants from the Multi-Ethnic Study of Atherosclerosis: insomnia with comorbid obstructive sleep apnoea, insomnia with objectively short sleep duration, and insomnia with fragmented sleep.6 The insomnia with comorbid obstructive sleep apnoea and the insomnia with short sleep duration were associated with increased circulating troponin T in older adults (the study did not include adults older than 79 years).6 Rapid eye movement (REM) sleep behaviour disorder is an early predictor of eventual phenoconversion to synucleinopathies.7 A study reported in 2023, analysed follow-up data from 1160 people from 28 centres of the International REM Sleep Behavior Disorder Study Group.