What's next? More research could give scientists a greater understanding of the brain cancer process, Alvarez-Buylla said.

But, for now, the research has no direct impact on the treatment of glioma patients, said Stiles, who co-wrote a commentary accompanying the study. Indeed, he said, one clinical trial has already shown that inhibiting the growth factor won't help patients with recurrent tumors.

Even so, Stiles said, the "line of attack" suggested in the study should be "reexamined and pursued."

More information

Learn more about brain malignancies at the American Cancer Society.

Kids Need More Exercise to Stave Off Future Heart Trouble

 THURSDAY, July 20 (HealthDay News) -- Kids have energy to burn, and experts currently recommend that children get an hour per day of exercise to help ward off heart trouble as adults.

But a new study suggests more activity may be needed.

"Current guidelines for physical activity in children may underestimate the necessary level for maintaining good health," said lead researcher Lars Bo Andersen, from the Norwegian School of Sports Science, Oslo. "We would suggest 90 minutes per day to prevent clustering of heart disease risk factors," he said.

His team's findings are published in the July 22 issue of The Lancet.

In their study, Andersen's team selected over 1,700 children, aged 9 or 15 years, from schools in Denmark, Estonia, and Portugal. In addition to measuring each child's amount of daily activity, the researchers also measured risk factors for cardiovascular disease, such as blood pressure, weight, waist circumference, insulin resistance (a precursor for diabetes), and blood cholesterol.

While previous studies into childhood activity simply asked kids how much exercise they got per day, Andersen's team equipped children with accelerometers -- devices that measure everyday activities such as moderate-intensity play and walking to school.

Most of the activities picked up by the accelerometer involve everyday activities and not high-intensity sports, Andersen noted. "If you think about the changes in physical activity that have happened over the years [and] which may have contributed substantially to the obesity epidemic, it is very likely that the decrease in activity is in mainly free activities," he said.

After four days of monitoring, Andersen's group found that the combined risk factor score for cardiovascular disease decreased as physical activity increased. The lowest risk factor scores were found in the 9-year-olds who did 116 minutes of moderate to vigorous intensity activity and the 15-year-olds who did about 88 minutes daily.

The researchers also found a dose-response relationship between health and physical activity, meaning that ordinary play activities do seem to be important for kids' health, Andersen said.

He noted that a "clustering of heart disease risk factors occurs even in healthy children, and the risk is more than three times higher among sedentary children compared to the physically active. We should do more to create a society where physical activity is a natural part of everyday living, and we should find effective strategies to increase the physical activity level among children."

Simple changes in children's routine and environment can help, Andersen said.

"We need to make it possible to live an active lifestyle, which means that children should play outside, they should walk or cycle to school, they should train their motor skills in school PE lessons," Andersen said. "Few parents or politicians have been aware of the health consequences of low habitual physical activity, because our children are not ill -- yet."

One expert agreed that physical activity for children needs to be reinforced at school and throughout daily life.

"The message here is clear: Move your body or lose your health," said Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center at Yale University School of Medicine in New Haven, Conn.

Unfortunately, levels of physical activity continue to decline in industrialized countries where technology does more and more of what muscles used to do at both work and play, Katz said. "The trend is especially noteworthy for children, as competing demands squeeze both physical activity and recess out of the typical school day, and [TV/computer] screen time replaces playground or backyard time," he said.

The case for ensuring that kids remain active is compelling, Katz said.

"For example, when schools don't have time for a dedicated hour of physical education, bouts of brief activity could be provided in the classroom during each session of the day. We have developed just such a program at my lab, under the name 'ABC (activity bursts in the classroom) for Fitness,' and are currently evaluating its benefits," he noted.

It seems ever more difficult for adults and children alike to maintain healthful levels of physical activity, Katz said. "We must find ways to put motion into our daily routine, and especially that of our children. Nothing less than their health, quality of life, and perhaps even life expectancy is at stake," he said.

More information

For more on exercise in childhood at the American Heart Association.