DEAR DOCTOR K:

My teenage son likes to sleep in on weekends, often until noon. Is it OK to let him do this?

DEAR READER:

I've been asked this question by nearly every parent of teenagers I know. I checked with my Harvard Medical School colleague, pediatrician Dennis Rosen, who confirmed what I've been saying: Letting your son sleep in on weekends isn't doing him any favors.

Teenagers should get nine hours of sleep per night. Most teens don't, especially during the school week. Instead, they stay up late to finish school work, take part in extracurricular activities and spend time with friends. As a result, they struggle to wake up on time for school. A few days of this, and they've built up a significant sleep deficit.

Sleeping late on Saturday and Sunday may fill that deficit, but it creates a bigger problem: It shifts your teen's inner clock further away from the external clock. That "inner clock" is kept in your brain. Your brain recognizes sunrise and sends signals throughout your body that prepares it to awaken and start functioning. Sunset does the opposite: A few hours after sunset, your body's inner clock starts to power down.

In teenagers, the body clock is somewhat different from what it will be when they become adults. The clock starts to power down the body at a later hour, and it also starts to power up the body at a later hour. That's why so many teens have trouble waking up in the morning.

So your son's body clock naturally causes him to fall asleep later and to get up later. When your son stays up even later than his body clock wants him to, to finish homework or to chat with his friends on Facebook, he is exaggerating the natural time shift of his body clock.

On top of that, by sleeping late on weekends, your son is exaggerating that time shift even further. He is experiencing the equivalent of a five-hour jet lag when it's time to get up on Monday morning. The alarm clock may be saying 6 a.m., but his inner clock is reading 1 a.m.. This will make it much harder for your teen to wake up, and to concentrate during the first hours at school. Over time, it can also significantly affect his mood.

As far as possible on weekends, try not to let your son sleep in more than an hour beyond his usual wake-up time. Here are some things you can do to get your teen out of bed:

-- Turn on all the lights in the bedroom and open the shades and curtains. Nothing says "wake up" more than bright light.
-- Set an alarm clock across the room and out of reach from your son's bed. -- Plan a morning outing with him.
In addition, don't let him nap during the day. Napping will make it harder for him to fall asleep at night, which will make it harder to wake up the next morning.

(Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.)

** ** **

COPYRIGHT 2013 THE PRESIDENT AND FELLOWS OF HARVARD COLLEGE
DISTRIBUTED BY UNIVERSAL UCLICK FOR UFS