Cognitive decline in short and long sleepers: a prospective population-based study (NEDICES)

Abstract

Background: It is not clear whether cognitive decline progresses more quickly in long sleepers than in short sleepers or than in participants with usual sleep duration. We assessed cognitive decline as a function of self-reported sleep duration in a prospective population-based cohort (NEDICES).

Methods: Participants were evaluated at baseline and 3 years later. Baseline demographic variables were recorded and participants indicated their daily sleep usual duration as the sum of nighttime sleep and daytime napping. The average daily total usual sleep duration was grouped into three categories: ≤ 5 h (short sleepers), 6-8 h (reference category), and ≥ 9 h (long sleepers). At baseline and at follow-up, a 37-item version of the Mini-Mental State Examination (37-MMSE) was administered.

Results: The final sample, 2715 participants (72.9 ± 6.1 years), comprised 298 (11%) short sleepers, 1086 (40%) long sleepers, and 1331 (49%) in the reference group (6-8 h). During the three year follow-up period, the 37-MMSE declined by 0.5 ± 4.0 points in short sleepers, 0.6 ± 4.3 points in long sleepers, and 0.2 ± 3.8 points in the reference group (p = 0.08). The difference between short sleepers and the reference group was not significant (p = 0.142); however, the difference between long sleepers and the reference group was significant (p = 0.040). In analyses adjusted for baseline age and other potential confounders, this difference remained robust.

Conclusions: In this study, cognitive test scores among long sleepers declined more rapidly than observed in a reference group. Additional studies are needed to confirm these results.

Keywords: Cognitive function; Elderly; Epidemiology; Population-based study; Sleep duration.

Figure 1

Flow-Chart of the Study

Figure 2. MMSE decline from baseline to follow up at the NEDICES Cohort

Mean baseline 37-MMSE scores are shown by open squares. Follow-up 37-MMSE scores are shown by closed squares. Mean ± 1 standard deviation are shown. Baseline scores were lower in shor and long sleepers than the reference group (those who reported to sleep 7 to 8 hours); moreover, during the three year follow-up period, these scores declined to a greater extent in long sleepers cases than in the reference group.