New evidence shows how sleep balances hormones and boost immunity, among other things, reports Scientific American in its October cover story.

“Do I really need to sleep?” As I travel around the world talking about sleep, I am asked this question over and over. The answer has always been clear—yes, everyone needs to do it. Just like hunger, thirst and sexual desire, the urge to sleep is a physiological drive. Exactly what spending a third of our lives unconscious gets us, however, has long mystified scientists.