How much sleep do we really need? A long asked question that has - after a very long study - been answered... we think.
David Dinges, from the University of Pennsylvania, is a sleep and chronobiology researched. He has been testing large groups of people in the lab to find out what happens to people when they have specific amounts of sleep each night.
Three groups were set up where some slept for 4 hours, 6 hours of 8 hours. And over two weeks the groups had to complete certain tasks designed to measure alertness, mental aptitude etc.