Slow-wave sleep and light sleep are associated with memory decline in late-life depression and mild cognitive impairment

Alterations in sleep stages are linked to cognitive decline. Examining these changes in high-risk disorders for dementia, such as late-life depression (LLD) and mild cognitive impairment (MCI), is crucial. This study investigated cross-sectional and longitudinal associations between sleep stages and cognition across LLD, MCI, and healthy control (HC) groups. We assessed 131 older adults (63 HC, 42 LLD, 26 MCI) using home-based actigraphy, cognitive tests, and MRI. We performed cross-sectional partial association analyses and longitudinal Generalized Estimating Equations to explore the associations between sleep and cognitive function. The LLD group exhibited significantly lower total sleep time (TST), sleep efficiency, and slow-wave sleep (SWS). Cross-sectionally, after adjusting for multiple comparisons, no robust stage-specific associations with cognitive domains were observed. Longitudinally, a lower SWS percentage significantly predicted memory decline in MCI, whereas a higher N1 light sleep percentage predicted greater memory decline in both LLD and MCI. Enhancing sleep depth may offer a vital strategy for preserving cognition in these at-risk populations.