Smartphones and teens at night: Not a good recipe for sleep, study says

Should teenagers use smartphones at bedtime?

The U.S. surgeon general, the National Sleep Foundation and the scientists behind hundreds of research papers tying screen use to adverse health impacts have answered this question: Definitely not.

Now, a new study by a Stony Brook University sleep expert and colleagues from other institutions has added empirical insight into just how deeply late-evening phone use impacts youngsters’ sleep time and quality.

The study, published online Monday in the journal JAMA Pediatrics, found that on nights when young people used their phones more than their own average, they fell asleep more than an hour later and slept more than 20 minutes less. Phone use shortly before sleep also correlated strongly with more time awake in bed after first falling asleep.

The researchers used data collected from 425 teens participating in the Adolescent Brain Cognitive Development Study, a National Institutes of Health-funded project that is the largest long-term study of brain development and child health in the United States.

Sleep interference

"What we’ve been saying for years, and what the totality of research supports, is that teens should not have phones in their bedrooms, because it interferes with sleep, which is fundamental for optimal functioning," said Lauren Hale, one of the study authors and a professor in the Department of Family, Population, and Preventive Medicine at Stony Brook Medicine.

Yihong Zhao, professor of data sciences at the Columbia University School of Nursing, and Dr. Dimitri Christakis, principal investigator at the Seattle Children’s Research Institute, collaborated with Hale on the study.   

Many earlier studies relied on self-reported data on sleep times and sleep interruptions. The new study used wearable fitness trackers to capture the youngsters’ sleep and heart rate data, along with a scientifically validated smartphone application that automatically tracked their phone use, which in the evening largely consisted of social media like YouTube or TikTok.

Phone use after 10 p.m. pushed back both the teens’ sleep onset and wake times — but the shift in wake times was smaller, cutting total sleep time and narrowing what researchers call the "sleep opportunity window."

Phone use in the 15 minutes before going to sleep was also associated with an increase in time periodically awake in bed over the first 30 minutes after sleep onset. The effect was even more pronounced when they used their phones in the last five minutes before sleep onset. 

Sleeping for memory

Early night sleep is important, among other reasons, because it supports "declarative memory formation" — the recollection of facts or events, for example, which a teen might need for a test or classroom discussion. Conversely, even short-duration sleep disruptions are harmful, the researchers wrote, because sleep "fragmentation" has been shown to impair next-day alertness and mood.

The teens in the study used their phones, on average, almost four hours every day, including about 40 minutes every night after 10 p.m. Girls recorded more screen time overall, but boys slightly more late-night phone use.

Hale said she found the screen time data point haunting.

"It’s taking away from something — sleep, paying attention at school, reading a book, playing soccer with friends, hanging out ... What is the opportunity cost?"

There is some debate over the mechanisms by which screen and smartphone use impair sleep, Hale said. Some scientists emphasize the light emitted by the devices, which suppresses melatonin, the hormone produced by the brain that regulates the body’s sleep cycle and makes you feel ready for sleep. Others, like Hale, focus on the cognitive, emotional and even physical stimulation screens and tablets provide.

"It’s the back and forth, the moving of the finger, hitting things, texting and waiting for a response: All of that is driving a lot of the problems," she said.

Dr. Daniel Bigman, a child and adolescent psychiatrist and sleep medicine physician at Northwell Health who was not affiliated with the study, said it provided "good, objective data to strengthen what we know" about screens, young people and health.

His advice is to "turn phones or any stimulating devices off an hour before bedtime, charge your phone outside the bedroom and use settings like Do Not Disturb, Sleep or Downtime mode. Parents, he said, should take care not to "use this as a punishment. Use it to protect sleep. Make it a routine."

Hale agrees that families should focus on a bedtime routine — something like brushing teeth and reading a hard-copy book, for example, that does not involve screens.

All the better, she said, if parents or caregivers follow that routine too. And if your teen says they need their phone’s alarm function to wake up in the morning, she recommends a device once found in many American bedrooms: "You can buy a very affordable alarm clock."

By Nicholas Spangler

nicholas.spangler@newsday.comspanglernewsday

Nicholas Spangler is a general assignment reporter and has worked at Newsday since 2010.