Getting too little or too much sleep can cause cognitive decline, according to a new study published in the journal Brain.


It seems as though the age-old saying "everything in moderation" applies to sleep, too. According to a new study highlighted by CNN and published in the journal Brain, getting roughly six to eight of hours of quality sleep most nights appears to delay cognitive decline and keep the brain sharp, even when the effects of early Alzheimer's disease were taken into account. "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," says first author Brendan Lucey, MD, an associate professor of neurology and director of the Washington University Sleep Medicine Center.

The findings suggest that there is a sweet spot for total sleep time where cognitive performance appears to be stable over time. To find this, researchers obtained sleep and Alzheimer's data on 100 participants whose cognitive brain function had been monitored for an average of four and a half years. Most (88) participants had no cognitive impairments, the rest were either very mildly impaired or had mild cognitive impairment. The researchers found that only participants who slept six to eight hours retained brain function.

woman sleeping soundly in bed at night time
Credit: GI/Tom Grill / Getty Images

Participants who slept fewer than five and a half hours appeared to have a decline in cognitive performance, even when researchers controlled for factors like age, sex, and Alzheimer's disease. The same results hold true for people who get a lot of sleep. Cognitive decline was noted in participants who slept for more than about seven and a half hours. "Short and long sleep times were associated with worse cognitive performance, perhaps due to insufficient sleep or poor sleep quality," Lucey says. 

Poor sleep is a common symptom of Alzheimer's disease, which is the main cause of cognitive decline in older adults and contributes to about 70 percent of dementia cases. The study is further proof of how important it is to start practicing good sleep habits early on. According to the Mayo Clinic, good sleep starts with a schedule—go to bed and get up at the same time every day. The health care company also recommends limiting daytime naps, staying physically active, creating a restful sleep environment, and monitoring what you eat and drink before bed. 


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