Four out of five teenagers with mobile devices keep them in their rooms overnight - and nearly a third of those bring them into their beds while sleeping - according a study Wednesday that offered new evidence that mobile devices undermine the rest necessary for peak health.
The study, based on a poll of 1,000 children and parents by consumer advocacy group Common Sense, offered the most comprehensive picture yet of the impact of mobile devices on teen sleep patterns, which researchers long have warned can undermine cognitive functioning and mental health while increasing obesity rates. The poll also found smartphones caused conflict within homes as many parents fear the devices are causing their teens to become "addicted."
But the most striking findings, according to researchers, concerned the round-the-clock nature of how teens use mobile devices. Many reported using their phones moments before bedtime, almost immediately upon rising and at least occasionally during the night; the main activities included checking social media, playing games and watching videos.
Many parents of teenagers reported similar - and equally worrying - habits about their own smartphone use.
"People are using their mobile devices all the time," said sleep researcher Lauren Hale, a professor of public health at Stony Brook University, who reviewed the study by Common Sense. "I'm not surprised by these numbers, but they certainly are high."
Common Sense, based in San Francisco, often criticizes Silicon Valley while advocating on behalf of parents struggling to manage teen technology use, but chief executive James P. Steyer said the new research should be a wake-up call, especially to mothers and fathers.
"It's a parent's responsibility to understand this in terms of their own sleep and in terms of their kids' sleep," Steyer said.
He also called on the technology industry, which over the past year has given parents new tools to limit their children's use of mobile devices, to mount public information campaigns publicizing the importance of restful sleep. Researchers consistently point to sleep as crucial to the mental and physical health of people, including teenagers.
"It's incumbent upon the industry to take a role in changing this behavior," Steyer said.
Psychologist Jean Twenge, who warned in her 2017 book "iGen" of the ill effects of social media and smartphone use by teens, called the Common Sense findings about devices in bedrooms "stunning and horrifying."
"I knew the problem was bad, but I didn't know it was this bad," Twenge said. "There's lots and lots and lots of studies in medical journals showing that people who keep their devices next to them when they sleep don't sleep as well, and they also don't sleep as long."
The blue light emitted by the screens of mobile devices has been associated with poor sleep, researchers say, but mobile devices also can cause emotional stimulation - through violent games or engaging forms of social media - that also can impair sleep or simply delay the moment when people fall asleep.
The Common Sense study, called "The New Normal: Parents, Teens, Screens, and Sleep in the United States," found that 68 percent of parents believe their teenage children spend "too much time" on their mobile devices, and 61 percent believe their teenagers are "addicted" - about the same as the group found in a similar study in 2016.
But teens themselves are feeling better about their use of mobile devices than in that study, when 50 percent reported feeling "addicted" to smartphones, compared with 39 percent in the study released Wednesday.
The concerns about the overuse of mobile devices are not limited to teens. Nearly half of parents surveyed reported feeling personally "addicted" to their devices, and 83 percent keep them in their bedrooms at night, with 12 percent keeping the devices in bed with them.
Teens also complained about how much their parents are using smartphones, with 38 percent of teens reporting that their parents are "addicted" to their mobile devices.
The overall margin of error for the poll was 4.4 percentage points.