How many hours of sleep a day do you think people need to stay healthy?

It all depends on the person. I've known some who do great on just four hours a night every night while others need closer to ten. Each body is different and it's very difficult to work in absolutes for it. For most though around six to eight seems to work. For myself I get about 4 hours at night and then maybe another two to four during the day. Mine gets broken up due to sleep issues.