Children and teenagers who spend lots of time in front of screens - especially TVs - tend to gain more weight as they age, according to a new study.

The findings are consistent with research suggesting all that idle sitting and exposure to advertisements may fuel poor eating habits (see Reuters Health story of May 9, 2012, here:).

Many parents believe their children are getting a reasonable amount of recreational screen time, Mark Tremblay said. But most U.S. and Canadian kids exceed the recommended two-hour maximum per day.

“We don’t pay attention to the fact that it’s half an hour here, half an hour there, an hour here, an hour there,” Tremblay told Reuters Health. He is the director of Healthy Active Living and Obesity Research at the Children’s Hospital of Eastern Ontario Research Institute in Ottawa, Canada, and wasn’t involved in the new study.

Researchers used data from a long-term study of kids who took surveys every other year. The surveys included questions about their height and weight as well as how much time they spent watching TV and DVDs and playing computer and video games.

Kids were between ages nine and 16 when the study started.

Out of about 4,300 girls in the study, 17 percent were overweight or obese. Twenty-four percent of the 3,500 boys were also above a healthy weight.

From one survey to the next, each one-hour increase in children’s daily TV watching was tied to an increase of about 0.1 points on a body mass index (BMI) scale, which measures weight in relation to height. That’s a difference of approximately half a pound per extra hour of TV.

Increases in total screen time between survey periods were linked with similar but smaller changes in BMI.

“The weight of the evidence is pretty strong that television viewing is related to unhealthy changes in weight among youth,” Jennifer Falbe said.

But, she told Reuters Health, “It’s important for parents to be aware of all the potentially obesogenic screens that they should really be limiting in their children’s lives.” Increases in DVD and video watching were tied to weight gain among girls, in particular.

Falbe led the study while at the Harvard School of Public Health in Boston. She is now at the University of California, Berkeley School of Public Health.

When kids watch TV, “There is more purposeful, deliberate exposure to eating options, commercials that come on that might cue you to go off to the pantry and grab a cookie or a soft drink,” Tremblay said.

“Typically your hands are free when you’re watching TV, so should that temptation capture you, you’re able to sit there and munch on whether it’s a healthy or an unhealthy snack.”

What’s more, he said, “You can get into a pretty much hibernative state on the couch.” Even if kids are sitting down while playing a computer game, for instance, they might be a bit more active, Tremblay said.

The study didn’t include many non-white or poor children, the researchers noted. So the findings may not apply to all U.S. youth.

Another study of factors affecting childrens’ weight published today in Pediatrics found that kids whose mothers and fathers reported consistent parenting - setting age-appropriate rules and expectations and following through on them - had a lower BMI than their peers. But those differences were small, Pauline Jansen from Murdoch Childrens Research Institute in Melbourne, Australia, and colleagues wrote.

In a third report in the same journal issue, researchers from the Centers for Disease Control and Prevention tracked 1.2 million children from low-income families in the U.S. to see how their weight changed over time.

They found 11 percent of kids who were not obese before age two became obese over the next two to three years. Close to two-thirds of children who were initially obese as babies and toddlers were no longer obese a couple of years later. Hispanic and American Indian/Alaska Native children were more likely than white kids to become obese and less likely to stop being obese.

The study “underscores the importance of early life obesity prevention in multiple settings for low-income children and their families,” according to researchers led by Dr. Liping Pan.

SOURCE: Pediatrics, online November 25, 2013.