The National Sleep Foundation recommends that we avoid looking at our screens for at least a full hour before tucking in for the night. That’s because the screen emits a blue light which interferes with melatonin, a hormone that regulates our sleep.

There's another reason to avoid late night screen-watching. A new Penn State University study reports that interactive screen use — such as texting or playing video games close to bed time — makes it take longer to fall asleep, especially for adolescents.

The study found that 15-year-old kids who used screens to communicate with their buddies, or to play video games before their bedtime, took up to a full 30 minutes longer to fall asleep than if they had gone to bed without engaging in interactive screen time.

“These tools are really important to everyone nowadays, so it’s hard to put a limit on them, but if you’re really looking out for an adolescent’s health, then you might consider limiting the more interactive activities, especially an hour before bed.”

The researchers also found that for each hour during the day that the teens extended the amount of time they played video games beyond their usual amount — for example, if they got a new game and bumped up their usual game-playing time — it took them an additional ten minutes to nod off.

Using daily surveys looking at the screen-centered activities of 475 teens for three or more days, the team asked the teen participants:

  • How many hours that day they spent communicating with their friends either by email, instant messaging, texting on their phones or through social media sites
  • How many hours they spent playing video games, surfing the internet and watching television videos
  • If they had participated in any of these activities in the hour before bed.

The researchers also used accelerometers for a week to find out how long the participants slept each night. During sleep research, an accelerometer records patterns of motion and non-motion, which differs between sleep and wake time.

Their findings showed that the teens spent:

  • An average of two hours a day communicating with friends via email, instant messaging, texting on their phones or through social media
  • Slightly less time about (1.3 hours) per day playing video games
  • Less than an hour a day surfing the internet
  • About 1.7 hours a day watching television or videos

In the hour before going to sleep, the teens said they communicated or played video games on their phone, computer or tablet 77 percent of the time and watched television or movies 69 percent of the time.

Overall, the accelerometer data showed that adolescents slept for an average of 7.8 hours a night, but for every hour during their days that they used screens to communicate, they fell asleep on average around 11 minutes later.

So, what’s the bottom line? “It’s a tricky situation,” Anne-Marie Chang, an associate professor of biobehavioral health and the study’s co-author, said in a press statement. “These tools are really important to everyone nowadays, so it’s hard to put a limit on them, but if you’re really looking out for an adolescent’s health, then you might consider limiting the more interactive activities, especially an hour before bed.”

The study is published in the Journal of Adolescent Health.