National Geographic

Sleep is seen as inter-rupting life, but thereal scourge is chronicsleeplessness. In Japanabout 40 percent ofthe population sleepsless than six hoursa night. Public dozing,as at this all-nightdiner in Tokyo,is socially accepted.PREVIOUS PHOTOWile, the seven-year-old son of pho-tographer MagnusWennman, watchescartoons on his iPad—a modern bedtimeritual for some. Thestimulation may driveoff sleep, but so doesthe backlit screen: Lightat night inhibits theproduction of mela-tonin, the hormone thathelps regulate our dailybiological rhythms.Americanssleep less thanseven hoursa night, abouttwo hours lessthan a centuryago. In ourrestless floodlitsociety, weoften thinkof sleep as anadversary.