Researchers found that about 40 percent of adolescents in 2015 slept less than seven hours a night, which is 58 percent more than in 1991 and 17 percent more than in 2009. They further learned that the more time young people reported spending online, the less sleep they got. Teens who spent five hours a day online were 50 percent more likely to not sleep enough than their peers who only spent an hour online each day. If you are a young person who cannot seem to get enough sleep, you are not alone. A new study led by San Diego State University Professor of Psychology Jean Twenge finds that adolescents today are sleeping fewer hours per night than older generations. One possible reason? Young people are trading their sleep for smartphone time. Most sleep experts agree that adolescents need nine hours of sleep each night to be engaged and productive students; less than 7 hours is considered to be insufficient sleep. A peek into any bleary-eyed classroom in the country will tell you that many youths are sleep-deprived, but it’s unclear whether young people today are in fact sleeping less.

The Monitoring the Future survey asked U.S. students in the 8th, 10th and 12th grades how frequently they got at least 7 hours of sleep, while the Youth Risk Behavior Surveillance System survey asked 9th-12th-grade students how many hours of sleep they got on an average school night. Combining and analyzing data from both surveys, the researchers found that about 40 percent of adolescents in 2015 slept less than 7 hours a night, which is 58 percent more than in 1991 and 17 percent more than in 2009. Delving further into the data, the researchers learned that the more time young people reported spending online, the less sleep they got. Teens who spent 5 hours a day online were 50 percent more likely to not sleep enough than their peers who only spent an hour online each day. For many, smartphones and tablets are an indispensable part of everyday life, so they key is moderation, Twenge stresses. Limiting usage to 2 hours a day should leave enough time for proper sleep, she says. And that’s valuable advice for young and old alike.