Studies show that people who sleep between 6.5 hours and 7.5 hours a night, as they report, live the longest. And people who sleep 8 hours or more, or less than 6.5 hours, they don't live quite as long. There is just as much risk associated with sleeping too long as with sleeping too short. The big surprise is that long sleep seems to start at 8 hours. Sleeping 8.5 hours might really be a little worse than sleeping five.