How much sleep do I really need to stay healthy long-term?

What we can tell you today: how thoroughly this has been studied.

Thoroughly studied

4 studies, of which 3 bring together the results of several trials in people. This is as strong as evidence gets.

This says how thoroughly something has been studied — not whether it works for you. What each study actually found is in the study itself, and in the plain-language write-ups we are adding.