Sleeping seven to eight hours a night is best for cognitive performance for most people, according to a large study in the journal Sleep in December 2018.

Canadian researchers had more than 10,000 English-speaking people from around the world complete online surveys and cognitive tests. Participants reported that they slept 6.4 hours per night, on average, during the past month. When the researchers correlated typical sleep durations with the cognitive test results, they found that, regardless of age, participants sleeping seven to eight hours per night performed best, on average, especially on tests of reasoning and verbal ability; short term memory was not affected by sleep duration. People who regularly slept less than seven hours a night and those sleeping more than eight hours were equally impaired.

In those who reported habitually shorter sleep hours, sleeping more than usual the night before testing (closer to the optimal amount) was associated with better performance, suggesting that a single night’s sleep can benefit cognition.

“While the relationship between too little sleep and cognitive impairment is perhaps unsurprising, it is less clear why too much sleep would produce a similar deficit,” the researchers noted.

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