Biomarkers

Poor sleep is linked to higher risk of Alzheimer's Disease (AD), yet its relationship with AD-related biomarkers is not fully understood. This study aimed to examine associations between objective sleep characteristics and three AD-related magnetic resonance imaging (MRI) biomarkers in a diverse cohort of community-dwelling older adults.

The Dormir Study recruited participants aged 50 and older enrolled in the ongoing Health and Aging Brain Study-Health Disparities (HABS-HD) cohort. Sleep characteristics were objectively measured using 7-day wrist actigraphy, capturing nighttime sleep duration, total time in bed (TIB), sleep efficiency (SE), wake after sleep onset (WASO) time, average awakening length, and sleep fragmentation index. AD-related MRI biomarkers included mean hippocampal volume, AD-signature cortical thickness, and white matter hyperintensity (WMH) volume. We performed multivariable linear regressions adjusting for age, sex, race/ethnicity, education, cognitive status, body mass index, smoking, alcohol consumption, and MRI scanners. We reported results using coefficient per 1-standard deviation increase in the continuous sleep exposures.

We examined 703 participants (mean age 66.4±8.4 years, 65.6% women), including 164 (23.3%) Black, 223 (31.7%) Hispanic, and 316 (45.0%) Non-Hispanic White individuals. Seventy-nine (11%) had nighttime sleep duration<6 hours, 462 (66%) had 6-8 hours, and 162 (23%) had >8 hours. After multivariable adjustment, nighttime sleep duration>8 hours [β = -0.16, 95% confidence interval (CI) -0.32, -0.002; compared to participants who slept 6-8 hours], longer TIB (β = -0.12, 95%CI -0.19, -0.05), WASO (β = -0.08, 95%CI -0.15, -0.01), and awakening length (β = -0.10, 95%CI -0.17, -0.03) were associated with smaller hippocampal volume. Similar patterns were observed for nighttime sleep duration>8 hours (β = -0.23, 95%CI -0.41, -0.04), longer TIB (β = -0.09, 95% CI -0.17, -0.02) and awakening length (β = -0.12, 95% CI -0.20, -0.04) with thinner cortex in AD-signature regions, but not for other sleep characteristics. No associations were found between sleep characteristics with WMH volume.

Nighttime sleep duration>8 hours and poor sleep quality, including longer TIB, WASO, and awakening length, were associated with worse AD-related MRI patterns among diverse community-dwelling older adults. Future longitudinal studies are warranted to validate the pathophysiological mechanisms underlying those sleep-AD associations.