The longer a teen spends on screen time throughout the day before going to bed, the worse quality sleep s/he is likely to have, suggests a large study published in the online journal BMJ Open.
The teens were asked how much screen time they spent outside of school hours, and on what activities, for any of the following electronic devices: computer; smartphone; tablet; games console; and TV, the study said
They were also asked questions about their sleep routine on weekdays and at weekends: when they normally went to bed and got up; how much sleep they needed to feel rested; and how long it took them get to sleep (sleep onset latency).
Gender differences emerged in activities and preferred devices. Games console use was more popular among the boys, whereas girls were more likely to use smartphones and tablets.
In particular, use of a computer, smartphone, or tablet in the hour before bedtime was significantly associated with taking longer to fall asleep. A period of more than half an hour is normally defined as long sleep latency in adults, say the researchers.
Total daytime screen use of more than 4 hours was linked to a 49 percent greater risk of taking longer than 60 minutes to fall asleep.
Studies show on average the teens said they needed 8-9 hours of sleep to feel rested. But those who spent more than 2 hours emailing or chatting online were more than three times as likely to sleep for less than 5 hours. While those who spent more than 4 hours in front of any screen were more than 3.5 times as likely to sleep for less than 5 hours.
When the analysis looked at individual devices, the strongest association for shortened sleep and less sleep than deemed necessary was found for computers, although this technology was one of the most commonly used of all the electronic platforms.
Multi-taskers were also more likely to take longer to get to sleep and to sleep for less—than those who used only one device.
Teens who used two to three devices were 50 percent more likely to sleep for less than 5 hours than those who used just one device; teens who used four or more devices were 75 percent more likely to do so, the study concluded.