The recommended eight hours’ shut-eye may not be enough, say researchers, as most people sleep for 90% of their time in bed, reports The Guardian.

Penn State University researchers claim we need 8.5 hours for sleep. Their reason? Most people only sleep 90% of their time in bed, so you need that extra half hour if you want to have eight hours real sleep.

Good sleep is worth the effort – but how long do you need?

0 hours Total sleep deprivation is literally torture. After three days you lose all sense of what is happening, and the body shuts the brain down in “microsleeps”. Eventually, you die. Not recommended.

Two hours No one lives with only two hours’ sleep every night. Yet many of us may end up with just two hours on special occasions. Not recommended, except in emergencies.