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 β = -0.12, 95% CI = -0.24 to -0.01). Midlife nightmares and insomnia were also associated with lower MMSE scores (fully adjusted β = -0.28, 95% CI = -0.49 to -0.07 and β = -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.