Lower and higher amounts of total sleep time are associated with reduced cognitive performance in older individuals
There may be a “sweet spot” in total sleep time for maintaining cognitive function during aging.
Background
Poor sleep is associated with diminished cognitive performance, especially in older adults. Studies in older people have also linked shorter and longer sleep times to decreased cognitive function. Although detrimental changes in sleep patterns are thought to play a possible role in Alzheimer’s disease (AD), the relationship between sleep, cognitive function, and AD is not well understood. This study examined the connection between sleep patterns and changes in cognitive function over time in a cohort of older participants.
The study
To test the idea that sleep patterns are linked to a decline in cognitive function, sleep-wake activity was monitored in 100 community-living participants, in addition to AD biomarker analysis in the cerebrospinal fluid (CSF) and annual cognitive testing.
The participants were all enrolled in another longitudinal study on cognitive function that involved yearly cognitive testing. At the start of this trial, the participants underwent 4–6 nights of sleep monitoring using sleep logs, actigraphy, and EEG (electroencephalography, to monitor brain waves). The final annual test of cognitive function was performed 1 year after sleep monitoring.
AD biomarkers were also analyzed within 1 year of sleep monitoring by measuring AD biomarkers in CSF samples. The participants were also analyzed for APOE genotype (some variants in the APOE gene are associated with Alzheimer’s disease).
The results
Among the sleep parameters examined, total sleep time, time in non-REM sleep, time in REM sleep, and low-frequency/non-REM/slow-wave activity seemed to be the most sensitive indicators for cognitive performance over time.
The relationship between these sleep parameters and cognitive function was nonlinear; both higher and lower amounts of total sleep were associated with reduced cognitive function, even after adjusting for AD biomarkers and APOE status. In the middle range of sleep time, cognitive function was stable over time. These results suggest that interventions to optimize sleep patterns may help to stabilize cognitive function during aging.
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