Electronic media devices are useful. They may be an inevitable part of modern life.
But whatever their virtues, these devices can also cause trouble.
The blue light emitted by electronic screens can reprogram the brain to delay the onset of sleep.
The exciting (and sometimes distressing) content of electronic media may do the same, prompting children to fall asleep later, and perhaps even awaken during the night.
And in countries throughout the world, the use of electronic media has been linked with sleep problems in children -- including delayed sleep onset, shorter sleep times, and daytime drowsiness.
How serious is this? What can we do about it?
Allowing children to use blue-light emitting devices before bedtime may be comparable to serving them a dose of caffeine, and studies suggest that most kids are at risk.
But if we take the time to understand why and how the electronic media undermine sleep, we can learn ways to protect sleep. By monitoring content, imposing an electronic "black out" period before bedtime, and using blue light filters, we can help kids sleep better.
Here is a guide to the evidence, and some tips for ensuring your children get the sleep they need.
A global change in the way kids experience nighttime
From North America to Europe to East Asia, studies reveal
that anywhere from 68 to 95% of children -- even toddlers under the age of 3 --
use electronic screens on a daily basis (Carson and Janssen 2012; Duch et al
2013; Jago et al 2013; Brindova et al 2015; Goh et al 2016).
When researchers have asked, the majority of both parents and kids confirm that children are using electronic screens in the hour leading up to bedtime. Some kids are even using these devices after bedtime.
For example, in a study of more than two thousand Italian youngsters, researchers found that 40% of children between the age of 1 and 3 use some sort of electronic screen within 30 minutes of bedtime. For kids under the age of 14, the number was 65% (Brambilla et al 2017).
In a large Canadian survey, 70% of 5th graders said they use an electronic device -- like a television, computer, or mobile phone -- within an hour of bedtime (Dube et al 2017).
Studies conducted in Norway and the United States suggest more than 70% of teens are using mobile phones or computers in the hour before bedtime (Hysing et al 2015; Grandisar et al 2013). And many adolescents continue to use electronic media throughout the night.
In a large Australian study, nearly half the teens said they used their mobile phones after bedtime, when they were supposed to be sleeping (Gamble et al 2014).
In two U.S. studies, almost 20% of teens said their technology habits awaken them during the night -- either because their phone rings (Grandisar et al 2014) or because they feel compelled to check their social media accounts (Power et al 2017).
So the use of electronic screens around bedtime has become a normal part of growing up, and many sleep researchers are concerned. Why?
To answer this, we need to look at several lines of evidence. Let's take them in turn.
For a long time, scientists have known that exposure to bright light before bedtime can delay the brain's production of melatonin, the hormone of drowsiness.
But in recent years, experiments have provided us with crucial details. Certain components of white light -- wavelengths in the range of 460-480nm -- may be particularly good at disrupting sleep.
This is the range of light that appears blue to our eyes, and it's the range that can trigger alertness even when lighting levels are dim.
Neurons in our retinas are tuned to respond maximally to blue light. They send a message to the brain: Wake up, be alert. It's daytime.
In experiments, the effects rival those of caffeine. For example, drivers can operate cars more safely in the middle of the night when their vehicles are lit with a dim, blue light (Taillard et al 2012; Beaven and Ekström 2013).
That's potentially useful for people who work night shifts. But it's bad news for people who want to sleep after watching videos, playing video games, using computers, or checking the messages on their mobile phones. Electronic screens emit blue light.
What's even worse is that children may be especially sensitive to the sleep-disruptive effects of artificial light.
In experiments on adults, researchers have found that youth matters. Given the same exposure to blue light, younger individuals tend to experience more sleep disruption (Gabel et al 2017).
As I write this in early 2018, nobody yet has published a similar experiment regarding children and blue light. But in a study using white light, Shigekazu Higuchi and his colleagues found that everyday levels of indoor lighting suppressed melatonin production in children -- even thought these same lighting levels had no discernible impact on adults (Higuchi et al 2014).
Commenting on this study, Monique LeBourgeois and her colleagues note "the magnitude of melatonin suppression in children was almost twice that of adults" (LeBourgeois et al 2017).
So while researchers are still putting together the pieces, the emerging picture isn't good. Would you pour your kid a cup of coffee an hour before bedtime?
Letting kids gaze into screens -- even dimly-lit screens in an otherwise dark room -- may seriously undermine their ability to sleep. And that doesn't take into account another factor. What about the content of electronic media?
Violent or scary media content is a common trigger of bedtime problems, and it plays an important role in children's nightmares, too.
For example, when Jan Van den Bulck questioned thousands of school children, he found that "TV content showed up frequently in nightmares for 33% of the children, and computer games were associated with nightmares in about 10% of boys and 5% of girls" (Van den Bulck 2004).
In another study, Michelle Garrison and her colleagues tracked more than 600 preschoolers, and found a clear link between electronic media use and sleep problems in children.
The more time preschoolers spent using electronic media in the evening, the greater their chances of having trouble falling asleep. Kids were also more likely to have nightmares, and to experience daytime tiredness (Garrison et al 2011).
Could this link be explained by reverse causation? Maybe preschoolers suffering from sleep troubles -- including nightmares -- are more likely to develop bedtime rituals that include nighttime media use. Their parents might be trying to soothe them to sleep with television.
That's possible. But it's interesting to note that researchers were able to reduce sleep problems in preschoolers by changing the content of the media that children consume.
Garrison and Dimitri Christakis randomly assigned hundreds of parents to replace their children's usual, violent TV content with nonviolent alternatives (like episodes of Sesame Street). Six months later, these kids were less likely than preschoolers in a control group to suffer from any sleep problems (Garrison and Christakis 2012).
Such results shouldn't surprise us, even if we've forgotten what it's like to be a child. In a study by Jan Van den Bulck and his colleagues (2016), adults who watched violent media content before bedtime were 13 times more likely to report having violent dreams afterward. You're probably very familiar with the power of media to affect sleep.
But it's important to remember that disturbing content is in the eye of the beholder. Something that doesn't strike you as frightening or particularly violent may bother your child.
It's also important to realize that kids don't have to be actively watching in order to suffer ill effects. Research suggests that passive television exposure can cause sleep problems in children -- as when a 5-year-old overhears a distressing story on the evening news (Paavonen et al 2006).
Finally, it isn't just threatening content that can cause sleep troubles. Sheer engagement -- including happy engagement -- can make it hard for children to wind down. For instance, research suggests that kids are more likely to stay up late playing a video game when it possess the quality of "flow" -- the experience of being sucked in, unaware of the external world (Smith et al 2017).
So electronic media content, like blue light, has the potential to disrupt sleep. And as we've seen, many kids are routinely using technological devices before bedtime.
In theory, this could be the perfect recipe for an epidemic of sleep problems in children. The question is: Do we see any evidence that this is happening? Is there reason to believe that electronic screens are having serious effects in the real world?
The study on preschooler media use is suggestive. But there are many more.
When Lauren Hale and Stanford Guan reviewed 67 studies
published between 1999 and 2014, they found that 90% of those studies linked
screen time with problematic sleep patterns -- mostly shorter sleep bouts and
delayed bedtimes (Hale and Guan 2015).
Research published since 2014 similar results (e.g., Carter et al 2015; Cheung et al 2017; Dube et al 2017; Falbe et al 2015; Harbard et al 2016).
For example, in one study researchers asked parents to report the sleep times of 715 infants and toddlers. They also asked parents whether or not these young children ever used touch screen devices.
When the researchers analyzed the results, they found that use of touch screens predicted fewer hours of nighttime sleep. Electronic media use also predicted longer delays between a child's bedtime and the time he or she actually fell asleep each night (Cheung et al 2017).
In another study, researchers asked more than 2000 older children (in the 4th through 7th grades) what time they fell asleep each night, and what time they woke up in the morning. They also asked kids about devices in their bedrooms (Falbe et al 2015).
As it turned out, both televisions and smaller electronic devices were independently associated with sleep loss.
Kids who slept near a small screen (like a tablet or mobile phone) reported sleeping an average of 21 minutes less than did kids who never slept near such a device. Kids with televisions in their bedrooms slept an average of 18 minutes less than kids without a bedroom TV.
For kids with multiple devices, the risk was additive. Children with both a television and one or more hand-held media devices in the bedroom averaged about 40 minutes less sleep than did kids without any tech in their rooms.
Such findings are consistent with the results of a recent parent-based survey. Researchers asked the parents of more than 200 kids (aged 8-17) what the youngsters usually did before bedtime, and how long they usually slept.
Compared to kids who didn't use devices before bedtime, kids who watched television or played video games slept, on average, 30 minutes less. Kids who used a mobile phone or computer before bedtime slept an hour less (Fuller et al 2015).
Taken together, these studies suggest that children are sleeping less because of electronic media. But the research mentioned here may represent the tip of the iceberg, because health is determined by more than the sheer number of hours a child sleeps.
What may be more important is sleep quality, and there's reason to think that electronic media use can undermine sleep quality in children. Nighttime exposure to electronic screens may interfere with deep sleep, increase night wakings, and make sleep feel less restorative. Across studies, bedtime access to electronic devices is consistently linked with daytime sleepiness -- a key indicator of poor sleep quality (Carter et al 2015).
Whenever we talk about correlations, we have to remember: Correlations don't prove causation. Sleep difficulties could be the cause of electronic media use as well as the effect. Some kids may use electronic screens more because they are night owls, and have more time at night to use media. Other kids may seek out electronic media to help them fall asleep.
So we shouldn't jump to the conclusion that electronic screens are to blame for every problem, or that every individual is similarly affected by exposure to electronic media.
Nevertheless, there is compelling experimental evidence regarding the disruptive effects of blue light. And the experimental intervention on preschooler media use confirms the idea that violent content matters. Replace it with friendly, reassuring content, and kids sleep better.
So I think it would be foolish to ignore the power of electronic media and electronic screens. What can we do? Here are some tips.
It's common sense to avoid potentially threatening content in the hours leading up to bedtime. But don't forget that daytime matters too. In the preschool studies, violent media content interfered with sleep even when children had viewed this content during the daytime only.
It's actually unclear if an hour is enough, especially for young children. But most studies looking for links with sleep trouble have focused on this time interval, and found that it made a difference.
A blackout rule can be hard to follow -- especially if you have a child who needs to do homework on a computer.
But whether you're concerned about a mobile phone, tablet, or PC, you should be able to find a blue light filter for it. In many cases, filters are applications that reset the color spectrum emitted by your screen. But some vendors also sell physical films that you can place on top of a screen. Unfortunately, there is no certification to ensure that a commercial filter is effective, so your best bet is to try one out and see how it makes you feel.
In laboratory experiments, volunteers who wore blue light shield eyewear for two hours before bedtime experienced higher melatonin secretion, greater drowsiness, shorter delays when trying to fall asleep (Ayaki et al 2016).
It's one of the ironies of the sleep industry -- night lights explicitly marketed to reduce anxieties and help children sleep often use blue light.
For more evidence-based information about improving your child's sleep, see this Parenting Science guide to solving sleep problems in children.
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Image of girl with blue light emitting device by Donnie Rae Jones / flickr