With their brains, sleep patterns, and eyes still developing, children and adolescents are particularly vulnerable to the sleep-disrupting effects of screen time, according to a new and sweeping review of the literature.
“The vast majority of studies find that kids and teens who consume more screen-based media are more likely to experience sleep disruption,” says first author Monique LeBourgeois, an associate professor at the University of Colorado Boulder. “With this paper, we wanted to go one step further by reviewing the studies that also point to the reasons why digital media adversely affects sleep.”
Of more than five dozen studies looking at youths ages 5 to 17 from around the world, 90 percent have found that more screen time is associated with delayed bedtimes, fewer hours of sleep and poorer sleep quality, the authors report. Biological, neurological and environmental factors all play a role:
Because their eyes are not fully developed, children are more sensitive than adults to the impact of light on the internal body clock, the paper notes.
“Light is our brain clock’s primary timekeeper,” LeBourgeois says, explaining that when light hits the retina in the eye in the evening hours it signals the circadian system to suppress 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.”
The authors point to one study that found that when adults and school-age children were exposed to the same amount and intensity of light, the children’s melatonin levels fell twice as much. 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 says.
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, the authors note.
A recent report from Commonsense Media showed mobile media device use has tripled among young children since 2011, with kids under 8 using them 48 minutes per day and many parents incorporating digital media into the bedtime routine.