Sleeping like a baby

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How much sleep do we need?

Everyone needs different amounts of sleep, but the general consensus is that adults require between six and eight hours of sleep per night [source: APA]. Nobody passed this information along to Leonardo da Vinci. He practiced something called polyphasic sleep -- taking 20- to 30-minute naps every few hours throughout the day and night. Some people are big on "Da Vinci sleep," but it's not generally endorsed by mainstream science.

The amount of sleep you need also changes as you age. Newborn babies have it made -- they sleep 16 to 18 hours every day. So if you're sleeping like a baby, you probably aren't getting much done. At the three-month mark, babies start to recognize day as day and night as night. This is called the circadian rhythm. By the time they hit one year, most of which is spent sleeping, babies slumber for 10 to 12 hours each night and nap another three to five hours. Pretty nice lifestyle. By preschool, those long naps aren't happening.

Once kids hit puberty, they'll need more sleep than in their prepubescent period. Their body clocks shift, making it tougher to fall asleep and harder to wake up in the morning. In fact, teenagers don't start producing their sleep hormones until 1 a.m., compared to 10 p.m. in adults [source: The New York Times]. So lay off, Mom and Dad -- the teenager who won't go to sleep and can't wake up is really pretty normal. Researchers performed tests on teenagers and found that taking away just one hour of sleep led to poorer test scores, reaction time, recall and responsiveness.

College is when things get really messy. Out from under the thumb of their parents, college students typically don't police the amount of sleep they need. One study reveals that one quarter of all college students are chronically sleep deprived [source: The New York Times]. Of course, they can always catch some Z's during that Botany 101 lab. But this sleepy state leads to more than bad grades and dozing in class -- 55 percent of all drowsy-driving fatalities occur under the age of 25 [source: Dement].

There's also such a thing as too much sleep, so the key is to get the right amount. A six-year study of one million adults showed that the highest mortality rates occurred in those who either slept less than four hours per night or more than eight hours [source: The New York Times]. More than eight hours on a regular basis can also lead to depression, high blood pressure and heart disease. So the incentive to get out of bed is more serious than "I'm hungry" or "I have to pee." If that's not enough, this next statistic should encourage you to set that alarm clock -- those who average more than nine hours of sleep per night are twice as likely to develop Parkinson's disease as those who get six hours or less [source: The New York Times].

­So now you know how much sleep you're supposed to be getting -- but what happens if you don't?