MONDAY, June 27 (HealthDay News) -- Sleep problems common to the toddler set are made worse both by violent media content and greater evening use of televisions, computers or video games, a new study suggests.

Reviewing parent surveys and media diaries from 617 preschoolers, Seattle researchers found that each additional hour of evening media use was linked to a significant jump in sleep problems, as was viewing of violent content at any time during the day.

On average, the kids consumed nearly 73 minutes of screen time daily, with 14 minutes occurring after 7 p.m. Children with TVs in their bedrooms logged more screen time and were more likely to have trouble sleeping.

"We definitely thought there would be an effect from violent content and evening content, but we saw that any evening content was a problem -- it didn't really matter for sleep if it was violent," said study author Michelle M. Garrison, a research scientist at Seattle Children's Research Institute. "Also, we had been assuming a lot of them were watching programs really intended for adults and teens, but the bulk of it was children's programs aimed at ages 7 to 12."

The study is published online June 27 and in the July print issue of the journal Pediatrics.

About 21 percent of pre-school children deal with at least two sleep problems, including difficulty falling asleep, nightmares, repeated night waking or daytime tiredness, according to the study authors. Prior research indicates that between 20 percent and 43 percent of American preschoolers also have televisions in their bedroom.

This study used media diaries that recorded all screen time for the children -- 55 percent of whom were boys and 18 percent from low-income families -- across one week, noting the screen title of TV, video game or computer usage and later coding it for ratings, content and pacing.

Researchers also focused on media use after 7 p.m. compared to the rest of the day, since median bedtimes in this age group are between 8 p.m. and 10 p.m.

Garrison said preschool children interpret many kinds of violence similarly, from slapstick cartoon pranks to true-life gunfights on the news, and found all types disturbed their sleep.

"For 3- to 5-year-olds, they're just really different in how they perceive media content compared to older children," she said. "Older kids can grasp what's real and what's not. To preschoolers, animated violence is just as scary as real violence."

Eighteen percent of study participants experienced at least one sleep problem five to seven days per week, the study said, and the most frequent issue was difficulty falling asleep. Kids with a bedroom TV -- who logged an additional 40 minutes of screen time each day -- were eight times more likely to have parent-reported daytime tiredness.

Michael Gilbert, a senior fellow at the Center for the Digital Future at the University of Southern California, said the findings aren't surprising, noting that they confirm prior research and reflect common sense.

But, "it's always valuable to extend our understanding and even just confirm our common sense assumptions," Gilbert said. "We're living in an age of massive data streams invading our worlds and, as always, parents have to shape the flow of information their children consume. The techno revolution we're now living through makes this responsibility ever more difficult to acquit."

Foregoing all media use among children may not be realistic, Garrison said, but curtailing it -- especially in the hour before bedtime -- is probably prudent.

"There are healthy media choices parents can be making," she said. "This gives parents information . . . in terms of preventing problems."

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The non-profit Common Sense Media offers ratings and advice on children's media.