WASHINGTON (Dispatches) -- A New research of older adults 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 researchers at Washington University School of Medicine in St. Louis say that their study suggests that there was 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, perhaps due to insufficient sleep or poor sleep quality.
They discovered a U-shaped relationship between sleep and cognitive decline. All in all, 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.
Alzheimer’s is the main cause of 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.