10) Your smarts may suffer. Sleep promotes learning, according to the Harvard Women's Health Watch. It helps the brain commit new information to memory, and researchers have found that people who sleep after learning a task do better on later tests. In 2011, University of London scientists said that getting less than six to eight hours of sleep a night can age your brain by four to seven years—increasing the speed of cognitive decline, and worsening vocabulary and reasoning abilities.
11) Kids may suffer more behavior problems. Research from a 2008 issue of the Archives of Pediatric and Adolescent Medicine found that children who are plagued by insomnia, short duration of sleeping, or disordered breathing with obesity, for example, are more likely to have behavioral issues like attention deficit hyperactivity disorder.
12) You'll look better. Beauty sleep is no myth: People are perceived as being less attractive and more unhealthy when they're sleep-deprived than when they're well-rested, according to research published in 2012 in the British Medical Journal. Swedish researchers photographed 23 volunteers on two occasions: Once, after getting eight hours of sleep, and again after being kept awake for 31 hours following five hours of sleep. None of the participants wore makeup and all were equally clean-shaven. More than 60 untrained observers rated the photos. Participants were judged to be 4 percent less attractive, 6 percent less healthy, and 19 percent more tired when they were sleep-deprived.
13) Death's doorstep may be nearer. Those who get five hours or less per night have approximately 15 percent greater risk of dying—regardless of the cause—according to three large population-based studies published in the journals Sleep and the Archives of General Psychiatry.
Updated on 3/5/12: This story was originally published on Oct. 16, 2008. It has been updated.