In a new study, researchers found that too little or too much sleep may contribute to declines in thinking.
Too little sleep was defined as four or fewer hours a night, while too much was deemed 10 or more hours a night. The ideal amount is seven hours a night.
The research was conducted by a team at Peking University.
In the study, the team collected data on more than 20,000 men and women. Participants reported their sleep habits and were given tests of cognition.
During follow-up, cognitive scores dropped faster among people with four hours or fewer and 10 hours or more of sleep per night than those who slept seven hours per night, the researchers found.
This association is called a U-shaped relationship because the effects of sleep on cognition are seen at both ends of the curve.
An increasing number of studies have found a U-shaped relationship between sleep duration and cognition, where both short and long sleep duration was associated with worse cognition.
According to the National Sleep Foundation, sleep is essential because it lets your body and mind recharge. The right amount of sleep also helps you stay healthy and prevent diseases.
Without proper sleep, the brain cannot function properly, impairing concentration, clear thinking, and memory-processing.
But the mechanisms underlying these associations remain unclear. It’s possible that inflammation might be related to excessive sleep.
Meanwhile, too little sleep might increase cerebrospinal fluid levels of amyloid plaque and tau protein, which are hallmarks of Alzheimer’s disease.
More than any other time in the circadian cycle, during sleep, the brain’s glymphatic system is active in washing out excess levels of toxins, including amyloid-beta peptide.
The team says each person probably has some optimum balance between sleep and amyloid clearance, with too much or too little of one causing the other to tip in the wrong direction.
The cognitive function should be monitored in individuals with insufficient or excessive sleep.
One author of the study is Yanjun Ma from Peking University Clinical Research Institute.
The study is published in JAMA Network Open.
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