Late nights spent in front of a screen are not good for anyone, but they are especially bad for children and teenagers. Their eyes, brain and sleep patterns develop throughout childhood and adolescence, so screen time at bedtime has a big impact, as a recent study of the mechanisms behind the sleep-disrupting effects of screen time shows.

Kids and teens who log more screen time are more likely to experience sleep disruption, Monique LeBourgeois, lead author of the study, told TheDoctor. “With this paper, we wanted to go one step further by reviewing the studies that point to the reasons why digital media adversely affects sleep.”

The larger pupils and more transparent lenses in the eyes of children and teens make exposure to digital screens a problem for the body's clock.

The researchers reviewed the findings of 67 studies of media use at night among kids and teens, ages five to 17 years old. In 90 percent of the studies, more screen time was associated with delayed bed time, fewer hours of sleep and poorer sleep quality.

The sleep problems are the result of a combination of biological, environmental and neurological influences. Light is the primary timekeeper for our body's internal clock, and because children’s eyes are not fully developed, they are more sensitive to the effects of light on that clock than adults' eyes are.

“We know younger individuals have larger pupils, and their lenses are more transparent, so their exposure and sensitivity to the light of a digital screen is even greater compared to older individuals,” LeBourgeois, an associate professor at the University of Colorado in Boulder, explained.

When light hits the retina in the eye during evening hours, it triggers the suppression of melatonin, a hormone that promotes sleep. All digital screens emit blue light, a particularly strong suppressor of melatonin.

The sleep-disrupting effects are made worse, according to the authors, by the “psychological stimulation” digital media delivers — whether a young person is viewing violent content or texting with friends. The increased cognitive arousal also disrupts sleep.

What Parents Can Do

“Digital media is not going away!” LeBourgeois said in an email, and added that it is not without some benefits. Parents can take a few easy steps to protect their children's sleep. LeBourgeois recommends they begin by talking with their children and teens about how important sleep is.

Limit your own digital media use, particularly at night, and keep a consistent sleep schedule.

They can use that conversation to encourage a bedtime routine without electronics. That means putting digital media away one to two hours before bedtime, and removing electronics from kids’ and teens’ bedrooms. If a child has to use a digital screen to complete an assignment, LeBourgeois recommends parents limit the intensity of the light or use an app that extracts the blue spectrum of light from the screen.

Parents' own digital media use matters, too, she adds. Set an example for your kids. Charge cell phones in a central location outside your bedroom and make sure kids do the same. Make a point of limiting your own digital media use, particularly at night, and keep a consistent sleep schedule.

LeBourgeois and her team recently began a study funded by the National Institute of Child Health and Human Development. Researchers visit the homes of volunteer families, expose children to different intensities of light and then collect saliva samples to measure changes in melatonin levels and the timing of the biological clock. The goal is to determine how little light it takes to affect sleep and circadian rhythms. The researchers then hope to develop evidence-based guidelines for parents and digital device makers.

The study is published in Pediatrics.