Moreover, the relationship held even after adjusting for factors that can affect both sleep and cognition, such as age, sex, levels of Alzheimer's proteins, and the presence of APOE4. The U-shaped relationship held true for measures of specific sleep phases, including rapid-eye movement (REM), or dreaming, sleep and non-REM sleep. EEG tends to yield estimates of sleep time that are about an hour shorter than self-reported sleep time, so the findings correspond to 5.5 to 7.5 hours of self-reported sleep, Lucey said. Overall, cognitive scores declined for the groups that slept less than 4.5 or more than 6.5 hours per night - as measured by EEG - while scores stayed stable for those in the middle of the range. The researchers found a U-shaped relationship between sleep and cognitive decline. The average age was 75 at the time of the sleep study. Most (88) had no cognitive impairments, 11 were very mildly impaired, and one had mild cognitive impairment. In total, the researchers obtained sleep and Alzheimer's data on 100 participants whose cognitive function had been monitored for an average of 4 1/2 years. For this study, the participants also provided samples of cerebrospinal fluid to measure levels of Alzheimer's proteins, and each slept with a tiny electroencephalogram (EEG) monitor strapped to their foreheads for four to six nights to measure brain activity during sleep. Such volunteers undergo annual clinical and cognitive assessments, and provide a blood sample to be tested for the high-risk Alzheimer's genetic variant APOE4. and Joanne Knight Alzheimer Disease Research Center. To tease apart the separate effects of sleep and Alzheimer's disease on cognition, Lucey and colleagues turned to volunteers who participate in Alzheimer's studies through the university's Charles F. Studies have shown that self-reported short and long sleepers are both more likely to perform poorly on cognitive tests, but such sleep studies typically do not include assessments of Alzheimer's disease. Poor sleep is a common symptom of the disease and a driving force that can accelerate the disease's progression. An unanswered question is if we can intervene to improve sleep, such as increasing sleep time for short sleepers by an hour or so, would that have a positive effect on their cognitive performance so they no longer decline? We need more longitudinal data to answer this question."Īlzheimer's is the main cause of cognitive decline in older adults, contributing to about 70% of dementia cases. Short and long sleep times were associated with worse cognitive performance, perhaps due to insufficient sleep or poor sleep quality. "Our study suggests that there is a middle range, or 'sweet spot,' for total sleep time where cognitive performance was stable over time. "It's been challenging to determine how sleep and different stages of Alzheimer's disease are related, but that's what you need to know to start designing interventions," said first author Brendan Lucey, MD, an associate professor of neurology and director of the Washington University Sleep Medicine Center. The findings could aid efforts to help keep people's minds sharp as they age. By tracking cognitive function in a large group of older adults over several years and analyzing it against levels of Alzheimer's-related proteins and measures of brain activity during sleep, the researchers generated crucial data that help untangle the complicated relationship among sleep, Alzheimer's and cognitive function. Poor sleep and Alzheimer's disease are both associated with cognitive decline, and separating out the effects of each has proven challenging.
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