Screens at bedtime and teen sleep

Introduction: Researchers tested whether reading on a bright tablet before bed changes how quickly teenagers fall asleep and how alert they feel the next morning.

Participants: Thirty-six students aged 15 to 17 (19 girls and 17 boys) from secondary schools in Zurich, Switzerland, with parental consent. None had a diagnosed sleep disorder or took medication that affects sleep. Race/ethnicity was not reported.

Method: Each student spent two nights in a sleep laboratory, one week apart. On one night, the student read a novel on a tablet set to full brightness for 90 minutes before lights-out at 10:30 p.m. On the other night, the student read the same kind of novel as a printed book under dim light. The order of the two nights was randomly decided for each student. Saliva samples taken every 30 minutes measured melatonin, a hormone that rises in the evening and helps bring on sleep. Electrodes recorded brain waves to show when the student fell asleep. Students were woken at 6:30 a.m. and rated how alert they felt (1 = very sleepy, 7 = very alert).

Results and Discussion: After reading on the tablet, the evening rise in melatonin came a mean of 48 minutes later than after reading the printed book. Students took a mean of 31 minutes to fall asleep after the tablet, compared with 19 minutes after the book. Morning alertness was lower after the tablet night (mean of 3.2 versus 4.1). All differences were statistically significant.

Introduction: Researchers surveyed teenagers to see whether phone use in bed is related to how long they sleep on school nights.

Participants: 4,210 students in grades 9 to 12 at 38 public high schools in Norway, chosen at random from schools across the country (51% girls). Race/ethnicity was not reported.

Method: Students completed an anonymous online questionnaire during class. They estimated how many minutes they usually spend on their phone in bed after turning off the lights on school nights, the time they usually fall asleep and wake up on school nights, how many hours of homework they do each night, and how often they feel too sleepy to concentrate in class.

Results and Discussion: Students reported sleeping a mean of 6 hours 50 minutes on school nights. More minutes of phone use in bed went with less sleep (r = −0.29). Students who reported 60 minutes or more of phone use in bed slept a mean of 58 minutes less than students who reported none, and were more than twice as likely to say they often felt too sleepy to concentrate in class. When the researchers took homework time into account, the relationship between phone use and sleep was weaker but still statistically significant (r = −0.18).

Introduction: Researchers tested whether keeping phones out of the bedroom helps teenagers sleep longer.

Participants: 120 students aged 14 to 17 (64 girls and 56 boys) at two high schools in Melbourne, Australia, with parental consent. Race/ethnicity was not reported.

Method: Students were randomly assigned to one of two groups for three weeks. In the phone-free group, students charged their phones outside the bedroom from 9:30 p.m. until morning. In the usual-routine group, students kept their normal habits. All students wore a wrist activity monitor that estimated when they fell asleep and woke up. Each school day morning, students rated how sleepy they felt in their first class (1 = not at all sleepy, 10 = extremely sleepy).

Results and Discussion: By the third week, the phone-free group fell asleep a mean of 19 minutes earlier and slept 21 minutes longer per school night than the usual-routine group, and they rated themselves less sleepy in their first class (mean of 4.6 versus 5.9). Both differences were statistically significant. Wake-up times did not differ, because both groups had to get up for school. Even in the phone-free group, students fell asleep after 11:00 p.m. on average.