There’s an old stereotype that says teenagers sleep too much.

Today, it appears that many of them aren’t sleeping enough, due to their use of smartphones, video games, computers and similar items.

That’s the conclusion of a study published recently in the journal B-M-J Open, which looked at electronic media use by almost 10,000 Norwegian youths, ages 16 to 19.

In the study, researchers surveyed teens in one Norwegian county in 2012. Participants were asked which of six popular electronic devices they used … and how much time they spent using these devices on weekdays, before and after school.

The researchers also asked what time the teens went to bed on weeknights and when they woke up.

It turned out that teens who spent a lot of time online were more likely to get less than the recommended eight to nine hours of sleep.

The researchers also found that virtually all the participants reported using electronic media during the last hour before they went to bed.

In the U-S, an estimated 97 percent of teenagers have at least one electronic device in their bedrooms. So the possibility of frittering away potential sleeping time is almost universal for U.S. teens.

This could be a serious problem for American youth. Long-term sleep deprivation can contribute to obesity, cardiovascular disease and early death.

Those are serious consequences for something that probably seems like harmless fun.

So perhaps parents should require smartphones, computers and other devices be kept in common areas of the home, where their use can be regulated.

Teenagers may cry foul at having their freedom curtailed. But it may be what’s best for their health.

And, unlike electronic media, teen discontent is something that parents have been dealing with for a very long time.