Overnight sleep features and next-morning brain metabolism in older adults

The relationship between sleep and brain metabolism remains poorly understood. This study aimed to determine whether overnight sleep features, estimated using a home sleep apnea system based on peripheral arterial tonometry, are associated with regional FDG-PET uptake in older adults.

We analyzed cognitively unimpaired participants (≥60 years) from the Mayo Clinic Study of Aging. Each participant underwent overnight objective sleep assessment with Watch PAT, followed by FDG-PET imaging the next morning. PET data were co-registered to 3T MRI and segmented into 47 regions of interest (ROIs) after estimating voxel number-weighted median FDG uptake across hemispheres. Associations between sleep macrostructure and sleep apnea/hypoxemia burden with regional FDG levels were examined using partial Spearman's rank correlations adjusted for age or grey matter volume (GMV).

Thirty-seven participants were studied (70.3% female, median age was 72 [IQR 68-78]). We found widespread negative associations between wake after sleep onset (WASO) and FDG level in cortical areas, primarily involving ventromedial/ventrolateral prefrontal cortex, lateral temporal and occipital cortices (ρ = -0.47 to -0.34, P < 0.05). Total sleep time was associated with FDG uptake in medial structures (ρ = 0.39 to 0.42, P < 0.05), including posterior cingulate, retrosplenial cortex, hippocampus, parahippocampus, thalamus and caudate. Hypoxic burden was associated with medial occipital FDG level (ρ = 0.35 to 0.39, P < 0.05). Regional GMV did not mediate these associations. WASO was associated with higher insomnia severity index and less restful sleep.

Sleep macrostructure and hypoxic burden exhibited significant associations with brain metabolism, potentially contributing to brain health, cognitive function, and daytime symptoms.