For 32 days, researchers from Harvard University asked people to follow a certain sleep schedule: Each night, half of them got eight hours of sleep and the others logged 5.5 hours. They found that the sleep-deprived participants took twice as long to react and lost their concentration five times as often while completing cognitive tasks.
Throughout the study, this group’s performance got worse and worse, says study author Elizabeth Klerman, MD, Ph.D., a physician at Brigham and Women’s Hospital and an associate professor of medicine at Harvard Medical School, both in Boston.
Plus, the participants didn’t think they were performing below average, even though they were. If you feel well-rested after sleeping fewer than seven hours, you’re probably still slower and less sharp than usual. (A small percentage of people can function on just five to six hours of shut-eye. Take our three-question sleep assessment to learn more.)
It doesn’t matter if you consistently go to bed late and wake up early—your body doesn’t adapt to sleep deprivation. Always aim for seven to 10 hours of shut-eye per night. “You should sleep enough that you don’t need an alarm to wake up,” Klerman says.
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