New submitter wrackspurt writes "Sleep deprivation has long been thought to be prevalent in the industrialized world. A new study (abstract) explains one very good reason why at least seven hours of sleep a night is necessary. Quoting the BBC: 'Sleep ramps up the production of cells that go on to make an insulating material known as myelin which protects our brain's circuitry. ... The increase was most marked during the type of sleep that is associated with dreaming - REM or rapid eye movement sleep — and was driven by genes. In contrast, the genes involved in cell death and stress responses were turned on when the mice were forced to stay awake.'"