Sleep condition and cognitive decline in Japanese community-dwelling older people: Data from a 4-year longitudinal study

This study examined whether sleep duration and excessive daytime sleepiness (EDS) are related to cognitive decline among community-dwelling older adults with intact cognition at baseline, using 4-year longitudinal data. A total of 3,151 community-dwelling older individuals aged >= 65 years were studied. They were assessed for cognitive function, including memory, attention, executive function and processing speed. Cognitive impairment was defined based on a score >1.5 standard deviations below the age- and education-specific mean. Cognitive decline was defined in one or more cognitive tests at follow-up. Self-reported sleep duration (short, <= 6.0 hr; medium, 6.1-8.9 hr; long, >= 9.0 hr) and EDS at first-wave examination were assessed and logistic regression analyses were used to examine the associations of sleep duration and EDS with cognitive status at second-wave examination. The incidence of cognitive decline differed significantly among the sleep-duration groups (short, 15.9%; medium, 11.9%; long, 20.1%; p = 0.001). The prevalence of having EDS was 13.1%, which was associated with a higher rate of cognitive decline than having no EDS (18.9% vs. 12.5%, p = 0.004). Long sleep duration compared with medium sleep duration (OR, 1.50; 95% CI, 1.05-2.13) and EDS (1.43; 1.01-2.03) independently impacted the incidence of cognitive decline. The results were similar after multiple imputations (long, 1.68, 1.12-2.52; EDS, 1.55, 1.05-2.29). In conclusion, our study revealed that both long sleep duration and EDS were independent risk factors associated with cognitive decline after 4 years among older adults.