(MayoClinic.com) Teens are notorious for staying up late and being hard to awaken in the morning. If your teen is no exception, it's not necessarily because he or she is pushing the limits or fighting the rules. This behavior pattern actually has a physical cause — and can be modified to improve your teen's sleep schedule.

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 factors such as part-time jobs, early-morning classes, homework, extracurricular activities, social demands, and use of computers and other electronic gadgets. More than 90 percent of teens in a recent study published in the Journal of School Health 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.

Although this might seem like no big deal, sleep deprivation can have serious consequences. Tired teens can find it difficult to concentrate and learn, or even stay awake in class. Too little sleep also might contribute to mood swings and behavioral problems. Another major concern is drowsy driving, which can lead to serious — even deadly — accidents.

The good news is that your teen doesn't have to be at the mercy of his or her internal clock. To help your teen develop better sleep habits:

• Adjust the lighting. As bedtime approaches, dim the lights. Then turn off the lights 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 might be refreshing. Be cautious, though. Too much daytime shut-eye might only make it harder to fall asleep at night.
• Curb the caffeine. A jolt of caffeine might 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. Discourage stimulating activities — including vigorous exercise, loud music, video games, television, computer use and text messaging — an hour or two before bedtime.
• Know when to unplug. Take the TV out of your teen's room, or keep it off at night. The same goes for your teen's cellphone, computer and other electronic gadgets.

Sleeping pills and other medications generally aren't recommended. For many teens, lifestyle changes can effectively improve sleep.

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 disrupt 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. You might notice loud snoring or intermittent pauses in breathing, often followed by snorting and more snoring.
• 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 his or her doctor. If your teen is depressed or has a sleep disorder, proper treatment can be the key to a good night's sleep.

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