Is sleep that important?

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?

Studies show that 60 percent of adults claim to have problems sleeping a few nights a week or more [source: APA]. The sales figures for sleeping pills support this claim -- they topped $3.7 billion in 2007 [source: Slate]. Studies also show that 40 percent of adults experience daytime sleepiness that interferes with their productivity at least a few days each month and 20 percent are sleepy a few days a week or more [source: APA]. Are you getting drowsy yet?

Some of the less dangerous effects of going without sleep include irritability, moodiness, a lack of inhibition and difficulty with focus and concentration. This is if you only miss out on a couple of hours of sleep. If you miss more than that, your friends are going to start to wonder what's going on -- you may experience slowed speech, apathy, impaired memory, deflated emotional response and an inability to multitask. If you stay awake past this point, you'll get extremely drowsy and actually fall into microsleeps -- nodding off for five to 10 seconds at a time. Not a big deal in a movie theater, but potentially fatal if you're behind the wheel of a car. In fact, there are 100,000 car crashes every year due to falling asleep while driving [source: sleepfoundation.org]. If you push it further without sleep, you'll begin to hallucinate.

Aside from these bothersome side effects, scientists are just now learning that getting too little sleep may also lead to some serious health problems. Researchers still don't have conclusive data, but chronic sleep deprivation has been linked to high blood pressure, cancer, heart disease, obesity and diabetes. And then there's a statistic that will have parents forcing their 5-year-olds to bed while it's still daylight -- teenagers who didn't get enough sleep as preschoolers are twice as likely to use alcohol, tobacco and drugs [source: APA].

The impact on high blood pressure, heart disease and diabetes stems from the theory that our bodies may get stuck in a state of alertness without enough sleep. This leads to an increase in the production of stress hormones, which increases blood pressure. Sleep deprivation also affects the functioning of the lining inside the blood vessels and can cause some low-grade inflammation that could lead to heart disease. The diabetes risk comes from the lack of insulin produced in sleep-deprived adults.

The link to obesity may be the most confounding. You'd think that sleeping all day like a hibernating grizzly bear would turn you into a lump of goo. It turns out that when you don't catch enough Z's, the two hormones that help keep your appetite in check get thrown out of whack -- leptin and ghrelin. (See "Is lack of sleep making me fat?" for more.)

For more information on sleep and the brain, please get out of your jammies and into some real clothes and check out the links on the next page.