Sleep characteristics and brain structure: A systematic review with meta-analysis

BACKGROUND: As the global population ages, the prevalence of associated conditions, including neurodegeneration and dementia, will increase. Thus, reducing risk factors is crucial to prevention. Sleep contributes to brain homeostasis and repair, which, if impaired, could lead to neurodegeneration. However, the relationship between sleep characteristics, disorders, and brain morphology is poorly understood in healthy adults. Therefore, we aimed to systematically analyse the literature and clarify how sleep characteristics are associated with brain structures.

METHODS: We systematically searched PUBMED, MEDLINE, ProQuest, Web of Science, and Scopus for empirical studies of healthy adults examining the associations between sleep characteristics or disorders and brain structure, adjusting for age, gender, and head size. We conducted a meta-analysis with random effects models for volumetric studies and a seed-based spatial analysis for voxel-based morphometry (VBM) studies.

RESULTS: One hundred and five articles (60 volumetric, 45 VBM) with 106 studies reporting 108,364 participants were included. Most studies (73.1%) found sleep characteristics and disorders to be associated with predominantly lower brain volumes (cross-sectional: 51.9% of all cross-sectional; longitudinal: 45.5% of longitudinal). In VBM studies, REM sleep behaviour disorder was linked to lower grey matter volume in the right frontal gyrus (z-score = -3.617, 68 voxels, p-value = <0 0.001).

CONCLUSION: Sleep characteristics - poor quality, short or long sleep - and sleep disorders are predominantly associated with lower brain volumes, suggesting that inadequate sleep (short, long or poor quality) might contribute to neurodegeneration. This insight highlights the importance of monitoring, managing, and enforcing sleep health to prevent or mitigate potential neurodegenerative processes.