Impaired Sleep Predicts Cognitive Decline in Old People: Findings from the Prospective KORA Age Study

Abstract

Study objectives: To investigate the association between sleep-related characteristics and cognitive change over 3 years of follow up in an aged population.

Methods: Sleep characteristics and covariates were assessed at baseline in a standardized interview and clinical examination of the population-based KORA Age Study (n = 740, mean age = 75 years). Cognitive score (determined by telephone interview for cognitive status, TICS-m) was recorded at baseline and 3 years later.

Results: At baseline, 82.83% (n = 613) of participants had normal cognitive status, 13.51% (n = 100) were classified with mild cognitive impairment (MCI), and 3.64% (n = 27) with probable dementia. The effect of three distinct patterns of poor sleep (difficulties initiating [DIS] or maintaining sleep [DMS], daytime sleepiness [DS] or sleep duration) were considered on a change in cognitive score with adjustments for potential confounders in generalized linear regression models. Cognitive decline was more pronounced in individuals with DMS compared to those with no DMS (β = 1.33, 95% CI = 0.41-2.24, P < 0.001). However, the predictive power of DMS was only significant in individuals with normal cognition and not impaired subjects at baseline. Prolonged sleep duration increased the risk for cognitive decline in cognitively impaired elderly (β = 1.86, 95% CI = 0.15-3.57, P = 0.03). Other sleep characteristics (DIS and DS) were not significantly associated with cognitive decline.

Conclusions: DMS and long sleep duration were associated with cognitive decline in normal and cognitively impaired elderly, respectively. The identification of impaired sleep quality may offer intervention strategies to deter cognitive decline in the elderly with normal cognitive function.

Keywords: cognitive decline; dementia; elderly; sleep.

Figure 1

Flow chart of the KORA Age study and the 3-year follow-up study, derived from the MONICA/KORA surveys.

Figure 2

The effect (β-estimate and 95% confidence interval (CI)) of patterns of poor sleep on cognitive decline (n = 740). (Exposure of patterns of poor sleep on cognitive decline were assessed in 3 separate models; model 1: difficulties in initiating sleep, difficulties in maintaining sleep and both; model 2: daytime sleepiness; model 3: sleep duration). The effect of difficulties initiating, or maintaining sleep, or both, were referenced to no sleep difficulties. The effect of daytime sleepiness (often and sometimes) was referenced to almost never daytime sleepiness.