We are used to thinking that every person needs 7-8 hours of sleep daily to feel good and be able to work efficiently. But do we need to sleep that long at one time or can we break our sleep in several shorter intervals? And what about numerous great people sleeping for only 4-5 hours for years? So how much sleep do we actually need?

Well, in fact, there were not so many great people in history who really slept less than 7-8 hours a day, for example, Wolfgang Amadeus Mozart, Thomas Edison or Sigmund Freud. Nowadays scientists admit that some 1-3% of the population can go well with just a few hours of sleep.

It is hard to check, but, for example, Yahoo CEO Marissa Mayer, Fiat CEO Sergio Marchionne, US President Barack Obama and Donald Trump claim to be sleeping 6 hours or less a night, thus they represent a so-called "sleepless elite".

Some of the scientists and artists slept even longer – 9-10 hours. And many of them – like Charles Darwin, Honoré de Balzac, Winston Churchill – divided their sleep in two parts: the major period at night and a short (sometimes not really short) nap during the day.

That is called biphasic sleep in contrast to monophasic (once a day). It is quite hard to imagine a TOP-manager sleeping at daytime. But still a biphasic sleep can be beneficial for those who are not able to sleep long at night because of phone calls, going to the bathroom or, of course, a crying baby.

A 2014 study (first of its kind!) compared the effects of one night of induced infrequent night-wakings (of 15 min, each requiring a purposeful response) and sleep restriction on sustained attention and mood in young adults. The results showed that “induced night wakings and sleep restriction both resulted in more OCPT omission and commission errors, and in increased depression, fatigue and confusion levels and reduced vigor compared to the normal sleep night”.

There are also several schedules of polyphasic sleep when a person sleeps more than two times in a 24-hour period. That is how human infants and some animals (such as cats) sleep.

Recently Matt Mullenweg, one of the most influential people on the web (according to Business Week and PC World), told in his interview to Tim Ferriss about his experience of polyphasic sleep.

He took six naps, each 40 minutes long, during a 24-hour period with 2,5 hours awake. And he said that was one of the most productive periods of his life – the time of creating WordPress.

Uberman Schedule is the most popular polyphasic sleep schedule because of it’s total 2 hours sleep. But it is believed that only about 5% of the population can handle it. More people can go well with an 8 nap schedule getting extra 40 minutes of sleep. The greatest danger of this scheme is deprivation of slow-wave sleep which is often called a deep sleep. Deprivation of sleep results in the build-up of free radicals and superoxides in the brain. That can seriously affect your health by causing depression, confusion, headaches, development of false memory, increased risk of diabetes and high blood pressure - and that's not the end of the list.

There are no documented facts of sustaining Uberman polyphasic sleep schedule for over a year with no serious health issues.

Matt Mullenweg also noted that it was hard to keep to his 6-naps schedule because of the social rules and he had to give this up after he met a girl.