How was sleep duration linked to brain amyloid and cognition in older adults?

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Disrupted sleep is common in aging and is associated with cognition. Age-related sleep changes are associated with multiple causes, including early Alzheimer disease pathology involving amyloid-β (Aβ), depression, and cardiovascular disease. The researchers investigated how self-reported sleep duration was associated with brain Aβ burden and demographic, cognitive, and lifestyle variables in adults with normal cognition.

This cross-sectional study used data from the Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) study, being conducted at 67 sites in the United States, Canada, Australia, and Japan. The analysis included people aged 65–85 who had an Aβ positron emission tomography (PET) scan and complete apolipoprotein E (APOE) genotype data. They were clinically normal according to a Clinical Dementia Rating score of 0 and cognitively unimpaired according to a Mini-Mental State Examination score of 25–30 and a Logical Memory Delayed Recall test score of 6–18. Data were analyzed from April 3, 2020, to June 20, 2021.

Self-reported nightly sleep was grouped as short (≤6 hours), normal (7–8 hours), or long (≥9 hours). It was compared with demographic characteristics, Aβ burden measured by a fluorine 18-labeled-florbetapir PET scan, objective and subjective cognitive function measures, and lifestyle variables. Among 4,417 participants, 2,618 were women (59%); mean age was 71.3 years (SD 4.7).

Shorter self-reported sleep was linearly associated with greater Aβ burden (β [SE] = -0.01 [0.00]; P = .005), and short sleep was associated with lower cognition, mostly in memory domains. Aβ burden did not differ between the long- and normal-sleep groups (β [SE] = 0.00 [0.01]; P = .99).

Compared with normal sleep, both short and long sleep were associated with higher body mass index (short vs normal: β [SE] = 0.48 [0.17], P = .01; long vs normal: 0.97 [0.31], P = .002), depressive symptoms (short vs normal: 0.31 [0.05], P < .001; long vs normal: 0.39 [0.09], P < .001), and daytime napping (short vs normal: 2.66 [0.77], P = .001; long vs normal: 3.62 [1.38], P = .01). Long sleep was associated with worse performance across multiple cognitive domains.

The authors concluded that both short and long sleep were associated with worse outcomes in older adults, emphasizing the importance of adequate sleep. This was a cross-sectional study, so the findings describe associations rather than establishing that sleep duration caused the differences.