It’s surprising how we spend our lives. Reach your 78th birthday and according to some back-of-the-envelope calculations, you will have spent nine of those years watching television, four years driving a car, 92 days on the toilet, and 48 days having sex.

But when it comes to time-consuming activities, there’s one that sits head and shoulders above them all. Live to 78, and you may have spent around 25 years asleep. In an effort to claw back some of that time it’s reasonable to ask: how long can we stay awake – and what are the consequences of going without sleep?

Any healthy individual planning to find out through personal experimentation will find it tough going. "The drive to sleep is so strong it will supersede the drive to eat," says Erin Hanlon, an assistant professor at the University of Chicago's Sleep, Metabolism and Health Centre. "Your brain will just go to sleep, despite all of your conscious efforts to keep it at bay."

Why sleep at all?



Exactly why the urge to sleep is so strong remains a mystery. "The exact function of sleep is still to be elucidated," says Hanlon. She adds, however, that there is something about sleep that seems to “reset” systems in our bodies. What’s more, studies have shown that routine, adequate sleep promotes healing, immune function, proper metabolism, and much more – which is maybe why it feels good to arise refreshed after a serious snooze.