Updated: Oct 25
Undoubtedly, you have heard that screen time too close to your child's bedtime is bad for sleep.
But to what extent is this true?
Is screen time bad only if your child is watching a show as they fall asleep?
What if they just like to watch a lot of TV during the day, but don't watch it in the evening?
Or, how about if watching a YouTube video on the iPad is the one thing that relaxes your child and seems to actually help him fall asleep?
Instead of speculating, or calling all screen time bad, I dove into the research on how screen time affects children's sleep.
Check out these 4 ways screen time can affect your child's sleep, according to science.
1. Light exposure before sleep alters sleep wake cycles
Many studies have shown that exposure to a bright light on a screen alters sleep-wake cycles and biological rhythms in people. Although most of these studies have been conducted in adults, it is thought that the same effects apply to children. Let's dive into the details.
It is not a new finding that nighttime melatonin can be suppressed by exposure to bright light. The first study showing this was conducted in 1980 and demonstrated that exposure to very bright light (about 2x the brightness of a typical office lighting) suppressed nighttime melatonin secretion. Many more recent studies, however, have shown these same effects at much lower light intensities (more like lighting in a typical well lit home).
A study (1) in 2003 by Higuchi et al., however, demonstrated suppressed nighttime melatonin at an even lower level of light intensity. During this study, the lighting of the room was very dim, but the display screen was bright. At this level of lighting, melatonin was found to be lower only when the activity on the screen was exciting (playing a game) as compared to boring (completing simple math problems). Melatonin levels were not affected if the activity on the screen was boring, even if the screen was bright. Nor were they affected if the screen was dim.
Researchers believe that because those performing the exciting activity maintained their gaze at the screen as compared to those performing a boring activity, the prolonged gaze impacted the decrease in melatonin. Additionally, the more exciting activity seemed to activate the subject's sympathetic nervous system, causing their pupils to be wider, thus letting in more light. The more light that is let in, the greater the effect on melatonin.
Without replicating this study on children viewing a show or playing a game, we don't know to what extent their typical activities on the screen would affect their melatonin levels. However, after seeing how my kids glue their eyes to the screens they are watching, I would suspect that a child watching a show would be closer to an exciting activity than a boring activity.
During the same 2003 study mentioned above, where the subjects were exposed to a bright or dim screen in a dimly lit room, participating in either exciting and boring activities, body temperature was measured as a marker of circadian rhythm. It was found that body temperature was higher, thus delaying circadian rhythm, in those viewing a bright screen performing an exciting activity. Researchers believe that body temperature is regulated by melatonin. Therefore, the delayed secretion of melatonin has been shown to actually delay the onset of the circadian rhythm.
Finally, in the same 2003 study mentioned above, sleepiness was not affected, despite melatonin levels being lower and circadian rhythm being altered. Thus, one may feel sleepy but be unable to fall asleep if the processes in their body are not lined up for sleep.
What Does This Mean?
With suppression of the nighttime melatonin, light exposure at night has the potential to substantially alter physiology and behavior. How?
Melatonin secretion can shorten, leading to less sleep.
Altered circadian rhythms impact hormone regulation including glucocorticoids. This can impact behavior, mental health, hormones, and the immune system. (4)
Avoid bright screens and exciting screen time activities in the evening
2. TV in the Evening Leads to More Sleep Disturbances
A study (3) by Garrison et al. in 2011 sought to find out if timing, content (see #4), co-use by an adult (see #4), or screen use in the bedroom (see #3) affected sleep in preschoolers. The researchers in this study found that preschool aged children who watched TV in the evening (after 7PM) reported more challenges related to sleep compared to those who did not watch TV after 7PM. They also found that for every additional hour of media use in the evening, sleep challenges worsened. Sleep challenges most commonly noted by parents included longer time to fall asleep (>20 minutes) and overnight waking.
Children who watched TV in the evenings (after 7PM) were also more likely to watch shows with ratings for older children or adults, although most of the content (80%) was the same as their daytime child-appropriate shows. Finally, this study found that while total daily screen time did negatively impact sleep, evening viewing had a greater impact than daytime viewing.
Additionally, a study (2) by Paavonen in 2006 found that children who watched TV in the evenings had a greater risk for Sleep-Wake Transition Disorder (see definition in #4).