One of the greatest things about growing older is that you get to stay up later. And it's not just your parents who make that decision. Your body gives you permission to enjoy the darker hours too.
Recent research has shown that brain changes during teen years make it easier for kids to stay up late (see "Teen Brains, Under Construction").
But just because you can stay up late, doesn't mean you should, scientists say. Young people who don't get enough sleep are often late for school, or they miss it completely, says a recent study by the National Sleep Foundation (NSF). Sleepy kids tend to be cranky and unhappy. And their grades suffer.
Just because you can stay up late doesn't mean that you should.
"If you're sleeping in school, you're not learning," says Mary Carskadon. She's a sleep researcher at Brown Medical School in Providence, R.I.
Lack of sleep is a growing problem in the United States, Carskadon says. Schools have been starting earlier in recent decades. And with TV, computers, and video games to distract them, people of all ages are sleeping less than their parents or grandparents did a few generations ago.
Sleep is important because it gives our bodies time to recover from the stress of living.
Studies show that adults who sleep less than 6 hours a night, night after night, have more heart problems and die sooner than do adults who sleep 7 to 8 hours a night.
How much sleep do you need? It depends in part on your age. Babies often snooze for most of the day. By the time they're 10 years old, kids need an average of 10 hours a night, says Carskadon.
Teenagers need to get plenty of sleep.
As they get older, kids tend to sleep less, Carskadon says. But given the chance in an experiment to sleep as long as they wanted to, young teenagers averaged about 10 hours of sleep. There's even some indication that teenagers may need more sleep than younger kids, she adds.
Our sleep-wake schedules may seem to be ruled by the need to get to school or work on time, but they're really under the control of our body's internal clock.
Every mammal has a "master clock" in its brain that tells its body what time it is and when it needs to sleep. Scientists recently discovered cells in the clock that collect information about light directly from the eyes, Carskadon says. When light comes in, the clock thinks that it's daytime.
Then, as darkness arrives, the body secretes a chemical called melatonin, which tells the clock that it's nighttime. By measuring levels of melatonin in saliva, scientists can see what time the master clock thinks it is.
"As kids start passing into middle school, melatonin secretion comes at a later time," Carskadon says. "That's why children who usually go to bed at 8:30 or 9 p.m. all of sudden start having trouble falling asleep" when they approach their teen years.
Reading or watching TV when you can't sleep only makes the situation worse. The extra light input pushes your master clock's sense of night ever later. If you find it easy to stay up until 1 a.m. and then sleep until noon, that's probably what has happened to you.
In a recent poll, more than one-quarter of the kids who took part in the survey said that they fell asleep at school at least once a week.
For our ancestors, this natural change in sleep patterns during the teen years was probably helpful for survival, Carskadon says. In those days, 15- and 16-year-olds were often responsible for staying awake to protect the tribe.
But these days, society doesn't make it easy for night owls. Some schools start as early as 7 a.m. Many kids get up and eat breakfast in darkness, then dash to catch the bus. This kind of schedule doesn't jibe with what's going on inside kids' brains.
The NSF's 2006 "Sleep in America" poll collected information about the sleep patterns of more than 1,500 U.S. kids, ages 11 to 17. The study found that only 20 percent of kids get the recommended 9 hours of sleep a night. On school nights, 45 percent get less than 8 hours.
So, it's probably not surprising that more than one-quarter of kids polled said that they fell asleep at school at least once a week. Roughly the same number reported being too tired to exercise.
That's a shame, says Phyllis Zee, director of the Sleep Disorder Center at Northwest Memorial Hospital in Chicago. Studies show that people who exercise regularly sleep best. That helps them keep fit. On the other hand, people who don't get enough sleep are more likely to gain weight and develop health problems.
Drinks that contain caffeine, along with TVs and other electronic devices, can make it hard to get enough sleep.
Some schools have pushed back their hours to accommodate the biological needs of their students. Minneapolis Public Schools, for example, switched school start times from 7:15 a.m. to 8:40 a.m. several years ago. Now, their students average an hour more of sleep a night. They show up at school more regularly, and their grades have improved.
Even if you can't change your school's schedule, you can get more sleep if you make it a priority, Zee says. Go to bed just 30 minutes earlier each school night, and you'll gain 2 1/2 hours of sleep a week.
Cutting out caffeine also helps. The NSF poll found that two-thirds of kids drink at least one caffeinated drink a day. Soda and coffee give your brain a jolt, but they can make it harder to fall asleep. Likewise, having more than four electronic devices in your bedroom is a sure way to lose sleep.
So, turn off the TV and computer, and switch off the lights. Your dreams are waiting!