It's important to look at how much time children spend being physically active and away from screens. (Toby Talbot/Associated Press)

The time spent in front of a TV or computer screen appears to be the main difference between Canadian teenagers who are overweight and their non-overweight peers, according to a new report.

The Canadian Institute for Health Information compared screen time — leisure time spent watching TV, playing video games and using a computer — among Canadians aged six to 11 and 12 to 17.

Researchers found 75 per cent of overweight teenage boys spent two hours or more in front of a screen, compared with 67 per cent among their non-overweight peers, according to the report released Thursday.

Among overweight children age six to 11, 48 per cent reported spending at least two hours a day in front of a TV or computer, compared to 31 per cent of their non-overweight peers.

'Stark difference' between female, male teens

"When we change the lens and we look at youth, we see a stark difference all of sudden between girls and boys," said the study's lead author, Lisa Corscadden, a senior analyst with the institute.

"Girls are way less active than they were even when they were children, and boys are still kind of active but not quite as much. The boys are spending a lot of time in front of the TV or computer, particularly [playing] video games."

It's not surprising that boys are spending so much time playing video games, she acknowledged. But the report's findings suggest that parents may want to limit screen time, not only for obesity but also for other benefits, such as improving reading scores, she said.

The findings show the importance of not only getting children to be physically active but also limiting their screen time, said Mark Tremblay, chief scientific officer for Active Healthy Kids Canada.

1 hour hockey game not enough

Going out for a bike ride or hockey practice helps, Tremblay said. "But it doesn't really justify then the next eight hours sitting idle in front of the screen, which a lot of us have almost been trained to believe.

"Especially as the inclement weather approaches, you don't necessarily have to be outside, you don't necessarily have to be joining a gym, but try to condition yourself to minimize the continuous minutes sitting idle."

Signing children up for swimming lessons or taking a dog for a walk can help, but parents should also promote spending time doing light physical activity like washing dishes, Tremblay said.

The researchers measured heights and weights. But a drawback of the study was that activity levels were self-reported, which could miss children who simply stood on the sidelines instead of running for a soccer ball, for example.

The report also looked at differences in fruit and vegetable consumption.

But other factors that make a difference to fruit and vegetable consumption, such as income, were not taken into account. The activity list in the survey also left out ones that girls might be more inclined to do, like socializing on the telephone or at the mall, Corscadden acknowledged.

Researchers used data from the 2004 Canadian Community Health Survey, that suggested more than a quarter of Canadian children age two to 17 are either overweight or obese.

Obesity levels among Canadians continued to rise until 2007 and then started to plateau, Corscadden said, noting the Public Health Agency of Canada is expected to issue an updated report on child obesity next summer.