Smartphones disrupt teenagers’ sleep

The study analyzed data from 425 children with an average age of about 15 years — participants in a long‑term project studying adolescent brain development. The researchers collected nearly 7,600 nights of observations.

The results showed that on nights when teenagers used their phones after 10:00 p.m. for longer than their personal average, they slept on average 20 minutes less and fell asleep almost an hour later — on average 64 minutes later. Those who didn’t put their phones down were more likely to wake up within half an hour after falling asleep. Every additional minute of smartphone use after ten p.m., beyond one’s personal norm, increased the time it took to fall asleep and reduced the total duration of sleep.

“In short, the study showed that the phone seems to shift the time of going to bed and makes it harder to transition into stable sleep,” says Daniel Bigman, a child psychiatrist and sleep medicine specialist at the Northwell Health network in New York. First, any activity before bedtime eats into sleep time: with a phone, a teenager simply goes to bed later. Secondly, the phone excites the brain: social media, videos, messages, notifications, and light are signals that, through the eyes and ears, tell the brain to stay alert when it’s time to calm down. “We know that light is one of the main sensory regulators of the sleep–wake cycle. On its own, it can shift our sleep cycle.”

According to the authors, this is one of the first studies to define a “smart” time to stop using the phone: research has shown that using it after 10:00 p.m. is associated with difficulty falling asleep and shorter sleep duration. Even a short session 5–15 minutes before falling asleep was linked to more frequent nighttime awakenings.

Fragmented sleep, Bigman explains, leads to impaired attention and concentration, irritability, and emotional reactivity in adolescents. It can increase stress levels and anxiety, contribute to a depressed mood, and also cause daytime drowsiness, reduced motivation, and even difficulties with self‑control and decision‑making.