Association of past and current sleep duration with structural brain differences: A large population-based study from the UK Biobank

Objective: This study aimed to examine the association between past/current sleep duration and macro -/microstructural brain outcomes and explore whether hypertension or social activity plays a role in such association. Methods: Within the UK Biobank, 40 436 dementia -free participants (age 40-70 years) underwent a baseline assessment followed by a brain magnetic resonance imaging (MRI) scan 9 years later. Past (baseline) and current (MRI scans) sleep duration (hours/day) were recorded and classified as short (<= 5), intermediate (6-8), and long (>= 9). Brain structural volumes and diffusion markers were assessed by MRI scans. Results: Compared with past intermediate sleep, past short sleep was related to smaller cortex volumes (standardized beta [95 % CI]: -0.04 [-0.07, -0.02]) and lower regional fractional anisotropy (FA) (-0.08 [-0.13, - 0.03]), while past long sleep was related to smaller regional subcortical volumes (standardized beta: -0.04 to - 0.07 for thalamus, accumbens, and hippocampus). Compared to current intermediate sleep, current short sleep was associated with smaller cortex volumes (-0.03 [-0.05, -0.01]), greater white matter hyperintensities (WMH) volumes (0.04 [0.01, 0.08]), and lower regional FA (-0.07 [-0.11, - 0.02]). However, current long sleep was related to smaller total brain (-0.03 [-0.05, -0.02]), grey matter (-0.05 [-0.07, -0.03]), cortex (-0.05 [-0.07, -0.03]), regional subcortical volumes [standardized beta: -0.05 to -0.09 for putamen, thalamus, hippocampus, and accumbens]), greater WMH volumes (0.06 [0.03, 0.09]), as well as lower regional FA (-0.05 [-0.09, - 0.02]). The association between current long sleep duration and poor brain health was stronger among people with hypertension or low frequency of social activity (all P-interaction <0.05). Conclusions: Both past and current short/long sleep are associated with smaller brain volume and poorer white matter health in the brain, especially in individuals with hypertension and low frequency of social activity. Our findings highlight the need to maintain 6-8 h' sleep duration for healthy brain aging.