According to a new study led by the Washington University School of Medicine in St. Louis, like many other things in life, sleep is best in moderation. Through a longitudinal study of older adults, scientists have discovered that both short and long sleepers experience greater cognitive decline than people who sleep moderately.
Both poor sleep and Alzheimer’s disease are associated with cognitive decline. Thus, separating the effects of each has proven challenging. By tracking the cognitive functioning of a group of 100 older adults over 4.5 years and analyzing it against levels of proteins related to Alzheimer’s disease and measures of brain activity during sleep, the scientists have shed new light on the complex relationship among sleep, Alzheimer’s disease, and cognitive functioning.
“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 study lead author Brendan Lucey, an associate professor of Neurology and director of the Washington University Sleep Medicine Center.
The researchers found that cognitive scores declined for the persons who slept either less than 4.5 hours or more than 6.5 hours per night, while scores remained stable for those in the middle of the range. While previous studies argued that short amounts of sleep lead to mental health issues, these new findings show that too much sleep can also be harmful. This suggests that sleep quality could be more important than quantity. Moreover, sleep problems appears to accelerate the brain damage caused by Alzheimer’s.
“Our study 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, perhaps due to insufficient sleep or poor sleep quality,” explained Professor Lucey.
“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.”
However, according to Lucey, each person’s sleep needs are unique and people who wake up rested on either short or long sleeping schedules should not feel compelled to change their habits.
The study is published in the journal Brain.