While physical activity is known to improve children's physical fitness and lower their risk of obesity, new research suggests it may also help them perform better in school.

Dutch researchers reviewed 14 previous studies from different parts of the world that looked at the relationship between physical activity and academic performance. Their review is published in the journal Archives of Pediatrics and Adolescent Medicine.

The data from the studies "suggests there is a significant positive relationship between physical activity and academic performance," wrote the authors, led by Amika Singh of the Vrije Universiteit University Medical Center's EMGO Institute for Health and Care Research in Amsterdam.

While they didn't examine the reasons why the relationship may exist, the authors, citing previous research, said regular physical activity seems to be linked to better brain function. The effect on the brain could be the results of a number of factors, including increased flow of blood and oxygen to the brain as well as higher levels of chemicals that help improve mood.

This latest report comes at a time when schools across the country debate cutting physical education from their curriculum or have already eliminated it because of budget constraints, the desire to stress academics or a combination of both. There is also concern that physical activity in schools can be detrimental to academic performance.

But in addition to the latest research review, a 2010 literature review done by the Centers for Disease Control and Prevention found that out of 50 studies, more than half showed a positive association between school-based physical activity -- such as physical education, recess and extracurricular sports -- and academic performance and about half found no effect. Only a few showed a negative relationship that could be attributable to chance.

Some of the research reported that concentration, memory, self-esteem and verbal skills were among the improvements noted in students who participated in school-based physical activity.

"School boards, school administrators and principals can feel confident that maintaining or increasing time dedicated for physical activity during the school day will not have a negative impact on academic performance, and it may positively impact students' academic performance," the CDC's authors wrote.

One of the reasons the Dutch authors decided to conduct their research review was concern over schools' emphasis on test scores.

"There is a focus on test scores and academic accomplishments, and there's a belief that schools need to cram all available time into academics," said Dr. David Geier, director of sports medicine at the Medical University of South Carolina in Charleston.

Geier was not involved in the Dutch research.

"The other problem," Geier said, "is that it becomes a funding issue for many schools."

If intellectual activities are incorporated with physical activities, Geier said, children will benefit both ways.

Geier's colleagues at the Medical University of South Carolina and a group of educators recently tried that combination at an elementary school. They incorporated 40 minutes of physical education every day that included a learning component for different grade levels. As an example, young children rode scooters while tracing shapes at the same time.

When the students took their spring standardized tests, more children achieved their score goal after the new physical education program than before it was implemented.

But even if there are no academic gains, physical activity in schools is still very important.

"There are cardiovascular benefits as well as decreased obesity and a decline in juvenile diabetes," said Geier.

"There's an even greater need for physical education now, because the vast majority of children's leisure activities are sedentary and involve technology," said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in the Bronx, N.Y. "The problem is our bodies were not designed with technology in mind. They were designed for physical activity, and both children and adults should use this ability or we risk losing it."

While they reported an overall positive association between activity and academics, the Dutch authors stressed their conclusion was "cautious" because very few studies they analyzed were scientifically strong.

"Only 2 of 14 studies were rated as being of high methodological quality, which is the minimum number of studies needed for 'strong evidence,'" they wrote.

The studies also measured physical activity and academic achievement differently, and physical activity information often relied on self-reporting, which can be unreliable.

Because of the limitations of the prior research, the authors said more "high-quality" research is needed to accurately measure the relationship between physical activity and school performance.

"To gain insight into the dose-response relationship between physical activity and academic performance, we need more high-quality studies using objective measures of physical activity," they wrote.