A study of 18,000 Japanese middle school and high school students showed that the use of cell phones at bedtime adversely affected sleep, which, as a result, impacted mental health.  Rachael Rettner says:

Looking at a bright display and performing tasks that excite the brain may change the production of melatonin, a hormone produced during sleep, and hurt the quality of a night’s rest, the researchers said.

One more reason to recommend keeping all electronics out of our kids’ bedrooms at night.

Read article:

Journal of Pediatric Psychology abstract here: