Sleep disturbances and change in multiple cognitive domains among older adults: a multicenter study of five Nordic cohorts.

STUDY OBJECTIVES: We examined and compared cross-sectional and longitudinal associations between self-reported sleep disturbances and various cognitive domains in five separate Nordic European longitudinal aging studies (baseline N = 5631, mean age = 77.7, mean follow-up = 4.16 years). METHODS: Comparable sleep parameters across studies included reduced sleep duration/quality, insomnia symptoms (sleep latency, waking up at night, and early awakenings), short and long sleep duration, and daytime napping. The cognitive domains were episodic memory, verbal fluency, perceptual speed, executive functioning, and global cognition (aggregated measure). A series of mixed linear models were run separately in each study and then compared to assess the level and rate of change in cognitive functioning across each sleep disturbance parameter. Models were adjusted for age, sex, education, hypnotic usage, depressive symptoms, lifestyle factors, cardiovascular, and metabolic conditions. By using a coordinated analytic approach, comparable construct-level measurements were generated, and results from identical statistical models were qualitatively compared across studies. RESULTS: While the pattern of statistically significant results varied across studies, subjective sleep disturbances were consistently associated with worse cognition and steeper cognitive decline. Insomnia symptoms were associated with poorer episodic memory and participants sleeping less or more than 7-8 hours had a steeper decline in perceptual speed. In addition, daytime napping (>2 hours) was cross-sectionally and longitudinally associated with all examined cognitive domains. Most observed associations were study-specific (except for daytime napping), and a majority of association estimates remained significant after adjusting for covariates. CONCLUSION: This rigorous multicenter investigation further supports the importance of sleep disturbance, including insomnia, long and short sleep duration, and daytime napping on baseline cognitive functioning and rate of change among older adults. These sleep factors may be targeted in future lifestyle interventions to reduce cognitive decline.

Sleep disturbances and later cognitive status: a multi-centre study.

OBJECTIVE: To investigate the associations between sleep disturbances in mid-life and late-life and late-life cognitive status. METHODS: In four population-based studies (three Swedish studies: H70 study, Kungsholmen Project (KP) and The Swedish Panel Study of Living Conditions of the Oldest Old (SWEOLD); and one Finnish study: Cardiovascular Risk Factors, Aging and Dementia (CAIDE)), participants provided self-reports on insomnia, nightmares and general sleep problems. Late-life cognitive status was measured by the Mini Mental State Exam (MMSE). The associations between late-life sleep disturbances and cognition 3-11 years later were investigated across all studies (n = 3210). Mean baseline ages were 70 (CAIDE, H70 and SWEOLD), and 84 years (KP). Additional analyses examined the association between midlife sleep and late-life cognition using CAIDE (21 and 31 years follow-up, n = 1306, mean age 50 years), and SWEOLD (20-24 years follow-up, n = 2068, mean age 58 years). Ordered logistic regressions, adjusted for potential baseline confounders, were used in the analyses. RESULTS: Late-life sleep disturbances were associated with poorer cognition after 3-11 years (fully adjusted ß = -0.12, 95% CI = -0.24 to -0.01). Midlife nightmares and insomnia were also associated with lower MMSE scores (fully adjusted ß = -0.28, 95% CI = -0.49 to -0.07 and ß = -0.20, 95% CI = -0.39 to -0.01), although the latter association was attenuated after adjusting for lifestyle/health-related confounders. Midlife general sleep problems were not associated with late-life MMSE performance. CONCLUSIONS: Sleep disturbances and midlife nightmares were associated with lower MMSE scores, which suggests that sleep disturbances in earlier life stages can be associated with worse late-life cognition.