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THURSDAY, Oct. 11, 2018 (HealthDay News) -- Seems that you can get too much -- as well as too little -- of a good thing when it comes to sleep.

In what's billed as the world's largest sleep study, too little or too much sleep can impair your brain, researchers report.

The study included more than 40,000 people worldwide who completed an online survey and a series of tests of mental abilities such as reasoning, memory and verbal skills.

Those who slept an average of seven to eight hours a night did better than those who got more or less sleep a night, preliminary results show. About half of the participants said they typically slept less than 6.3 hours a night.

The researchers noted a number of surprising findings. Most people who slept four hours or less performed as if they were almost nine years older, and the amount of sleep associated with the best test results was the same for all ages.

Reasoning and verbal abilities were two of the mental skills most strongly affected by sleep, while short-term memory was relatively unaffected by sleep patterns, the researchers said.

There was some evidence that even a single night's sleep can affect thinking abilities. Participants who slept more than usual the night before taking the tests did better than those who slept their usual amount or less.

The study was published Oct. 9 in the journal Sleep.

"We really wanted to capture the sleeping habits of people around the entire globe. Obviously, there have been many smaller sleep studies of people in laboratories, but we wanted to find out what sleep is like in the real world," said study co-author Adrian Owen, a researcher in Cognitive Neuroscience and Imaging at the University of Western Ontario, Canada.

"People who logged in gave us a lot of information about themselves. We had a fairly extensive questionnaire and they told us things like which medications they were on, how old they were, where they were in the world and what kind of education they'd received because these are all factors that might have contributed to some of the results," Owen explained in a university news release.

Study lead author Conor Wild, a research associate in Owen's lab, said, "We found that the optimum amount of sleep to keep your brain performing its best is seven to eight hours every night, and that corresponds to what the doctors will tell you need to keep your body in tiptop shape, as well."

More information

The U.S. National Institute of Neurological Disorders and Stroke has more on sleep.

SOURCE: University of Western Ontario, news release, Oct. 9, 2018

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