New US research has revealed that teenagers are sleeping fewer hours per night than generations before them, with evidence suggesting that smartphones could be to blame.
Led by San Diego State University along with professors from Iowa State University, the research looked at data from two long-running, nationally representative surveys of more than 360,000 teenagers.
One survey asked students in the 8th, 10th and 12th grades how often they got at least 7 hours of sleep, while the other asked 9th-12th-grade students how many hours of sleep they got on an average school night.
After looking at both sets of data together, the team found that around 40% of adolescents in 2015 slept less than 7 hours a night, which is 58% more than in 1991 and 17% more than in 2009.
The findings also showed that the more teens reported spending online, the less sleep they got, with those who reported spending 5 hours a day online 50% more likely to not get enough sleep compared to those who only spent an hour online each day.
Most sleep experts agree that adolescents need 9 hours of sleep each night to be productive and perform their best at school. Less than 7 hours a night is considered to be insufficient sleep.
As figures show that smartphone use increased dramatically from 2009, lead author Jean Twenge believes that this could be to blame for the 17% increase between 2009 and 2015 in the number of students sleeping 7 hours or less, with Twenge commenting that "Teens' sleep began to shorten just as the majority started using smartphones. It's a very suspicious pattern."
Previous research suggests that smartphones can have a negative effect on sleep not only because teens stay up later using them, but also because blue light emitted by smartphones and devices such as tablets can interfere with the body's natural sleep-wake rhythm, also reducing the quality of sleep.
This can lead to teens feeling exhausted the next day and even dropping off during daytime hours when they should be alert and engaged students.
"Our body is going to try to meet its sleep needs, which means sleep is going to interfere or shove its nose in other spheres of our lives," explained co-author Zlatan Krizan. "Teens may catch up with naps on the weekend or they may start falling asleep at school."
As smartphones have become such an essential part of life, Twenge recognizes that a solution may be moderation rather than giving them up completely, stressing that limiting usage to 2 hours a day will give more time for quality sleep, adding that it is useful advice for both teens and adults.
"Given the importance of sleep for both physical and mental health, both teens and adults should consider whether their smartphone use is interfering with their sleep," she added, "It's particularly important not to use screen devices right before bed, as they might interfere with falling asleep."
The findings can be found published online in the journal Sleep Medicine.