If you’re only getting six hours of sleep each night, you might be just as sleep deprived as someone who got zero hours of sleep for two days.

A team of researchers at the University of Pennsylvania School of Medicine analyzed 48 individuals who were divided into four groups namely, eight hours, six hours, four hours and no hours of sleep. Their cognitive functions were analyzed every two hours they were awake.
At the end of the 15-day study, they found that participants who got eight hours of sleep regularly performed the best and those who slept for four hours were the worst.
At first, participants who slept for six hours every day were feeling fresh and performed better for some days, but in the long run, their cognitive performance declined and matched to that of persons who did not sleep for two days straight.
The study suggested that sleeping hours depend on each individual but managing to get more than six hours will benefit people and protect against sleep deprivation.
Source-Medindia