(MayoClinic.com) Teens are notorious for staying up late at night and being hard to awaken in the morning. Your teen is probably no exception, but it's not necessarily because he or she is lazy or contrary. This behavior pattern actually has a physical cause — and there are ways to help mesh your teen's sleep schedule with that of the rest of the world.

Everyone has an internal clock that influences body temperature, sleep cycles, appetite and hormonal changes. The biological and psychological processes that follow the cycle of this 24-hour internal clock are called circadian rhythms. Before adolescence, these circadian rhythms direct most children to naturally fall asleep around 8 or 9 p.m. But puberty changes a teen's internal clock, delaying the time he or she starts feeling sleepy — often until 11 p.m. or later. Staying up late to study or socialize can disrupt a teen's internal clock even more.

Most teens need about nine hours of sleep a night — and sometimes more — to maintain optimal daytime alertness. But few teens actually get that much sleep regularly, thanks to part-time jobs, homework, extracurricular activities, social demands and early-morning classes. More than 90 percent of teens in a recent study reported sleeping less than the recommended nine hours a night. In the same study, 10 percent of teens reported sleeping less than six hours a night.

Big deal? Yes. Irritability aside, sleep deprivation can have serious consequences. Daytime sleepiness makes it difficult to concentrate and learn, or even stay awake in class. Too little sleep may contribute to mood swings and behavioral problems. And sleepy teens who get behind the wheel may cause serious — even deadly — accidents.

Catching up on sleep during the weekends seems like a logical solution to teen sleep problems, but it doesn't help much. In fact, sleeping in can confuse your teen's internal clock even more. A forced early bedtime may backfire, too. If your teen goes to bed too early, he or she may only lie awake for hours.

So what can you do? Don't assume that your teen is at the mercy of his or her internal clock. Take action tonight!

• Adjust the lighting. As bedtime approaches, dim the lights. Turn the lights off during sleep. In the morning, expose your teen to bright light. These simple cues can help signal when it's time to sleep and when it's time to wake up.
• Stick to a schedule. Tough as it may be, encourage your teen to go to bed and get up at the same time every day — even on weekends. Prioritize extracurricular activities and curb late-night social time as needed. If your teen has a job, limit working hours to no more than 16 to 20 hours a week.
• Nix long naps. If your teen is drowsy during the day, a 30-minute nap after school may be refreshing. But too much daytime shut-eye may only make it harder to fall asleep at night.
• Curb the caffeine. A jolt of caffeine may help your teen stay awake during class, but the effects are fleeting. And too much caffeine can interfere with a good night's sleep.
• Keep it calm. Encourage your teen to wind down at night with a warm shower, a book or other relaxing activities — and avoid vigorous exercise, loud music, video games, text messaging, Web surfing and other stimulating activities shortly before bedtime. Take the TV out of your teen's room, or keep it off at night. The same goes for your teen's cell phone and computer.

Sleeping pills and other medications generally aren't recommended for teens.

In some cases, excessive daytime sleepiness can be a sign of something more than a problem with your teen's internal clock. Other problems can include:

• Medication side effects. Many medications — including over-the-counter cold and allergy medications and prescription medications to treat depression and attention-deficit/hyperactivity disorder — can affect sleep.
• Insomnia or biological clock disturbance. If your teen has trouble falling asleep or staying asleep, he or she is likely to struggle with daytime sleepiness.
• Depression. Sleeping too much or too little is a common sign of depression.
• Obstructive sleep apnea. When throat muscles fall slack during sleep, they stop air from moving freely through the nose and windpipe. This can interfere with breathing and disrupt sleep.
• Restless legs syndrome. This condition causes a "creepy" sensation in the legs and an irresistible urge to move the legs, usually shortly after going to bed. The discomfort and movement can interrupt sleep.
• Narcolepsy. Sudden daytime sleep, usually for only short periods of time, can be a sign of narcolepsy. Narcoleptic episodes can occur at any time — even in the middle of a conversation. Sudden attacks of muscle weakness in response to emotions such as laughter, anger or surprise are possible, too.

If you're concerned about your teen's daytime sleepiness or sleep habits, contact your teen's doctor. If your teen is depressed or has a sleep disorder, proper treatment may be the key to a good night's sleep.

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