Sleep, 24-Hour Activity Rhythms, and Cognitive Reserve: A Population-Based Study.

BACKGROUND
The cognitive reserve hypothesis aims to explain individual differences in susceptibility to the functional impact of dementia-related pathology. Previous research suggested that poor subjective sleep may be associated with a lower cognitive reserve.


OBJECTIVE
The objective was to investigate if actigraphy-estimated sleep and 24-hour activity rhythms are associated with cognitive reserve.


METHODS
This cross-sectional study included 1,002 participants from the Rotterdam Study (mean age: 65.0 years, standard deviation (SD): 7.1) who were assessed with actigraphy, five cognitive tests, and brain-MRI between 2009- 2014. Sleep and 24-hour activity rhythms were measured using actigraphy (mean days: 6.7, SD: 0.5). Cognitive reserve was defined as a latent variable that captures variance across cognitive tests, while adjusting for age, sex, education, total brain volume, intracranial volume, and white matter hyperintensity volume. Associations of sleep and 24-hour activity rhythms with cognitive reserve were assessed using structural equation models.


RESULTS
Longer sleep onset latency (adjusted mean difference: - 0.16, 95% CI: - 0.24; - 0.08) and lower sleep efficiency (0.14, 95% CI: 0.05; 0.22) were associated with lower cognitive reserve. Total sleep time and wake after sleep onset were not significantly associated with cognitive reserve. After mutual adjustment, only the association of longer sleep onset latency remained significant (- 0.12, 95% CI: - 0.20; - 0.04). The 24-hour activity rhythm was not significantly associated with cognitive reserve.


CONCLUSION
In conclusion, our study suggests that longer sleep onset latency is particularly associated with lower cognitive reserve. Future longitudinal work is needed to assess whether shortening the sleep onset latency could enhance cognitive reserve, in order to limit the susceptibility to the functional impact of dementia-related pathology.