Sleep, brain power and all the things that your gadget may be stealing from you.
Illustration: Dominic Xavier/Rediff.com
Adolescents today are increasingly depriving themselves of sleep, and instead spending more time on their smartphones or other devices, say scientists who found that teens sleep fewer hours per night than older generations.
Most sleep experts agree that adolescents need nine hours of sleep each night to be engaged and productive students; less than seven hours is considered to be insufficient sleep.
Researchers from San Diego State University and Iowa State University in the United States examined data of more than 360,000 US school students who took part in a survey.
The study, published in the journal Sleep Medicine, found that about 40 per cent of adolescents in 2015 slept less than seven hours a night, which is 58 per cent more than in 1991 and 17 per cent more than in 2009.
Delving further into the data, researchers 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 per cent more likely to not sleep enough than their peers who only spent an hour online each day.
Beginning around 2009, smartphone use skyrocketed, which researchers believe may be responsible for the 17 per cent bump between 2009 and 2015 in the number of students sleeping seven hours or less.
Not only might teens be using their phones when they would otherwise be sleeping, but research suggests the light wavelengths emitted by smartphones and tablets can interfere with the body's natural sleep-wake rhythm.
"Teens' sleep began to shorten just as the majority started using smartphones," said Jean Twenge, from San Diego State University in the US.0
Of more than five dozen studies looking at youths aged five to 17 from around the world, 90 per cent have found that more screen time is associated with delayed bedtimes, fewer hours of sleep and poorer sleep quality.
According to another study, this is because children and teenagers are more vulnerable to the blue light emitted by smartphone screens disrupting sleep. Since their eyes are not fully developed, children are more sensitive than adults to the impact of light on the internal body clock, they said.
"The vast majority of studies find that kids and teens who consume more screen-based media are more likely to experience sleep disruption," said Monique LeBourgeois, associate professor at the University of Colorado Boulder in the US. "We wanted to go one step further by reviewing the studies that also point to the reasons why digital media adversely affects sleep."
When light hits the retina in the eye in the evening hours it suppresses the sleep-promoting hormone melatonin, delaying sleepiness and pushing back the timing of the body clock.
"We know younger individuals have larger pupils, and their lenses are more transparent, so their exposure and sensitivity to that light is even greater than in older individuals," he said.
Studies have also shown that short-wavelength 'blue light' -- ubiquitous in hand-held electronics -- is particularly potent at suppressing melatonin. "Through the young eyes of a child, exposure to a bright blue screen in the hours before bedtime is the perfect storm for both sleep and circadian disruption," LeBourgeois said.
The "psychological stimulation" of digital media -- whether it's exposure to violent media or texting with friends -- can also sabotage sleep by boosting cognitive arousal.
LeBourgeois's study also noted that children and adolescents who leave a phone or computer on overnight in their bedroom are significantly more likely to have trouble sleeping.
More than 75 per cent of youths have screen-based media in their bedrooms, 60 per cent interact with them in the hour before bedtime, and 45 per cent use their phones as an alarm.
Students might compensate for that lack of sleep by dozing off during daytime hours, said Zlatan Krizan from Iowa State University.
"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. Teens may catch up with naps on the weekend or they may start falling asleep at school."
For many, smartphones and tablets are an indispensable part of everyday life, so they key is moderation, Twenge said.
Limiting usage to two hours a day should leave enough time for proper sleep, she said.
"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 said. "It's particularly important not to use screen devices right before bed, as they might interfere with falling asleep."