By Maria Cheng,AP Medical Writer

LONDON – Doctors may soon have a prescription for health that even kids will like: more playtime.

European and international health experts say a new study makes the most convincing case yet for the benefits of children being active. They say the research may lead to new guidelines saying youngsters between ages 5 and 16 need to be active up to 11/2 hours a day.

For some parents, that might be accomplished simply by showing their children the door.

“Just making sure children play outside will double the amount of physical activity they get,” said Dr. Lars Bo Andersen, lead author of the research published Friday in the medical journal Lancet.

Experts said the study doesn’t mean children need to be on treadmills or in soccer leagues – they just need to be able to run around and play physically, even for short bursts of time.

Concerned by flaws in previous studies, Andersen and his colleagues set out to examine the connection between children’s physical activity and risk factors for heart disease and diabetes.

The study looked at 1,732 9-year-olds and 15-year-olds from Denmark, Estonia and Portugal. Physical activity was monitored for four consecutive days by strapping little machines to the youngsters’ hips, which monitored accelerations in body movements.

Despite differences among the three countries where children were monitored, the benefits of physical activity were consistent. The more active children had healthier numbers for blood pressure, cholesterol and insulin.

“This effect is not dependent on one country or one ethnic group, and it is probably applicable in almost any population,” said Dr. Ram Weiss, a pediatrician at the Hebrew University Medical School, and author of a commentary in Lancet on Andersen’s study.

Because it measures activity objectively, without relying on questionnaires, Andersen’s research may lead to a reconsideration of physical activity guidelines by countries and global health organizations.

“This is much stronger evidence than we’ve ever had before,” said Nick Cavill, a research associate in the public health department at Oxford University, who wasn’t involved in the study.

About 40 percent of those monitored were reasonably active, while the rest were sedentary, researchers said. The study found that the benefits of physical activity applied to all children – not just to obese children, normally thought to be at higher risk.

While much attention has been paid to children’s bad eating habits, Andersen’s study calls for equal weight to be placed on activity levels.

“It would be a mistake only to look at this as an obesity problem,” he said. “A lot of children have metabolic problems without being fat. … It’s a question of getting them to be more active and less sedentary.”

However, parents shouldn’t take that to mean that a radical change in their children’s routine is necessary.

“We don’t need to be getting kids running in the gym on treadmills,” said Cavill. “We need to encourage kids to play.” One of the study’s key findings, he explained, is that it proves the utility of short bursts of activity, rather than a need for continuous exercise.

The researchers said physical activity does not demand intense exercise, such as playing soccer or tennis. “There is a value to five- and 10-minute bouts of activity, where kids will run for a little while and then stop,” said Cavill.

Pushing more physical activity for kids requires government policy changes, which Andersen said have already started to happen in some countries. For instance, schools in Denmark and Norway now include more physical education classes.

Designing schools and neighborhoods to be child and exercise-friendly would also help.

“Urban planners need to put more focus on things like road safety and the design of a neighborhood, so that children will be safe when they’re playing outside,” said Roar Blom, a physical activity expert with the World Health Organization.

But perhaps the greatest factor in children’s physical activity will be the parents themselves.

“It’s not just that children should be more active, it’s the whole family,” said Weiss. “Parents should be role models.”