The researchers conducted an experiment involving 48 people aged 21-38 years, which broke into four groups, according to Russian newspaper. During the first two weeks was sleeping eight hours a day, the second six and the third for four hours. The fourth group had to spend without sleep for three days.

During the experiments, the researchers regularly checked the level of cognitive functioning of participants and the speed of their response.

It was found that those who slept for eight hours a day, showed the best results, while those who slept only four hours a night, coped worse with tests for all days.

However, the biggest surprise for researchers was the group's results, sleeping six hours. It turned out that it is well kept, but only about 10 days of testing. In the last days of the experiment, she experienced the same decrease in the level of productivity, as people who were not allowed to sleep. Six hours sleep was comparable in effect to a forced "insomnia", which lasted for two days in a row. And although representatives of this group did not feel particularly drowsy, however, "lack of sleep" obviously affected the test results.

The results of the study appeared in the journal Sleep.