A new study is the latest to link blue-light emitting devices, like laptops, phones and game consoles, to shorter sleep in adolescents.
"There are probably many possible pathways between screen time and sleep, some of which are direct," said lead author Mari Hysing of Uni Research Health in Bergen, Norway. "The light from the screens may directly affect our circadian rhythms, and teenagers may be especially sensitive."
As reported in the journal BMJ Open, she and her co-authors analyzed survey responses from almost 10,000 teens, ages 16 to 19, in Western Norway.
More than 90 percent of girls and 80 percent of boys reported using a cell phone in the hour before bed, and laptops were almost as common.
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Throughout the day, girls reported an average of 5.5 hours of screen time with any device – a personal computer, cell phone, MP3 player, tablet, game console or TV – and boys averaged almost seven hours per day. A large proportion of those hours were spent chatting online. Boys and girls spent an average of half an hour each day on emails.
Boys averaged almost an hour on console video games and more than an hour on PC games.
Using any device in the hour before bed was associated with a 13 to 52 percent increase in the likelihood of needing more than 60 minutes to fall asleep, the researchers found.
More than four daytime hours of screen time was associated with a similar increase in risk of "sleep latency", or taking a long time to fall asleep.
Sleep deficit link
Screen time was also linked to an increased risk of a sleep deficit of at least two hours, meaning the kids said they needed two more hours of sleep than they were actually getting.
The teens tended to use many devices at once, so it was hard to compare them and see if certain devices were more strongly linked to sleep quality, Hysing said.
Several studies recently have showed that the more frequently young people use these media devices, the greater the chance their sleep will be disturbed, said Michael Gradisar, a clinical psychologist and sleep researcher at Flinders University in Adelaide, South Australia.
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"This study by Hysing and colleagues was eye-opening because they showed that screen use above the recommended two hours per day was associated with sleep durations well below the norm, and in the range we see linked with poor school performance, emotional disturbances, and in some cases suicidal ideation," Gradisar, who was not part of the new study, told Reuters Health by email.
"There is now much evidence, including this study, to suggest that screen time has a direct effect on sleep," Hysing told Reuters Health by email.
But, Hysing said, it could also be that "some families who do not have fixed bedtimes for their teenagers are the same who do not limit screen time."
Also, she said. "We know that depressed teenagers often sleep less, and this might also be related to screen time use."
This study only included data from one point in time, so there is no way to prove that using screens caused a change in sleep patterns, said Emma Adam, a developmental psychologist at North-western University in Chicago.
"We can't rule out the possibility that they use screens more because they can't sleep, but certainly there is other evidence that screen time right before bed affects sleep," Adam told Reuters Health by phone.
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The National Sleep Foundation recommends that teens avoid eating, drinking, or exercising within a few hours of their bedtime and try to avoid the TV, computer and telephone in the hour before going to bed.
"While there has been a focus on media use in younger children, we know that many teenagers do not have parental-set bedtimes nor restrictions on media use," Hysing said. "The most important thing we can do is to keep the night screen free."
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Image: Students looking at their phones and tablet pc from Shutterstock