Like so many other good things in life, sleep is best in moderation.
In a new study from Washington University in St. Louis, researchers found that both short and long sleepers experienced greater cognitive decline than people who slept a moderate amount, even when the effects of early Alzheimer’s disease were taken into account.
The finding suggests that there is a middle range, or ‘sweet spot,’ for total sleep time where cognitive performance was stable over time. Short and long sleep times were associated with worse cognitive performance.
Alzheimer’s is the main cause of the cognitive decline in older adults, contributing to about 70% of dementia cases. Poor sleep is a common symptom of the disease and a driving force that can accelerate the disease’s progression.
In the study, the team tracked cognitive function in a large group of older adults over several years and analyzed it against levels of Alzheimer’s-related proteins and measures of brain activity during sleep.
In total, they obtained sleep and Alzheimer’s data on 100 participants whose cognitive function had been monitored for an average of 4 1/2 years.
Most (88) had no cognitive impairments, 11 were very mildly impaired, and one had mild cognitive impairment. The average age was 75 at the time of the sleep study.
The researchers found a U-shaped link between sleep and cognitive decline.
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.
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.
The U-shaped link held true for measures of specific sleep phases, including rapid-eye movement (REM), or dreaming, sleep; and non-REM sleep.
The findings suggest that sleep quality may be key, as opposed to simply total sleep.
The team says each person’s sleep needs are unique, and people who wake up feeling rested on short or long sleep schedules should not feel compelled to change their habits. But those who are not sleeping well should be aware that sleep problems often can be treated.
If you care about Alzheimer’s disease and dementia, please read studies about this health problem can make Alzheimer’s disease more dangerous and findings of new tests can detect very early signs in Alzheimer’s disease before symptoms appear.
For more information about Alzheimer’s detection and prevention, please see recent studies about people with these 2 mental problems may develop Alzheimer’s early and results showing a new method for an effective prevention of Alzheimer’s disease.
The study is published in the journal Brain. One author of the study is Brendan Lucey, MD.
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