An extra hour of exercise a week could significantly cut obesity among overweight girls, according to a study that researchers say could lead to major changes in the way schools fight obesity.
The study, the largest look yet at obesity among young children, did not show the same results for boys, possibly because they generally get more exercise than girls.
Still, Dr. Rebecca Unger, a pediatrician at Children's Memorial Hospital in Chicago, said the findings show the important role schools can play in preventing obesity.
Unger said the study highlights the importance of funding daily physical education in schools, where about 15 percent of children and adolescents are overweight, according to government figures.
"This is incredibly serious if you consider the medical and emotional consequences of obesity. The further along these problems progress the more at risk these children are," Unger said.
In the study of 11,000 children, researchers compared changes in the body mass index _ a measure of weight relative to height _ of obese and overweight girls in kindergarten and first grade.
They found the prevalence of obesity and being overweight among the girls fell 10 percent in schools that gave first-graders one hour more of exercise time per week than kindergarteners.
Based on that, the researchers think that giving kindergarteners at least five hours of physical education time per week _ the amount recommended by the government _ could potentially reduce the prevalence of obesity and overweight among girls by 43 percent.
"This has the ability to affect tens of thousands, if not hundreds of thousands, of children. The implications are so big because this is something we can do as a society," said Nancy Chockley, president of the National Institute for Health Care Management Foundation.
The Washington, D.C., nonprofit group recently released a research brief on the study, and two other studies of childhood obesity.
The analyses were done by the Rand Corp., a think tank that used data collected by the Department of Education as part of a long-term study of 11,192 children from about 1,000 schools who entered kindergarten in 1998.
The results released so far are only for those youngsters' kindergarten and first-grade years. Data on their third-grade and fifth-grade years will be released later.
Yale University obesity researcher Kelly Brownell said the findings are significant because they demonstrate the importance of making sure children get adequate physical activity.
But he said exercise must be tied with better eating habits _ including rethinking school lunch programs and the presence of school vending machines laden with high-calorie snacks _ to fully address the nation's growing epidemic of childhood obesity.
"This is probably the strongest statement yet that physical activity may help prevent obesity. But we have to remember that it's not going to compensate for the unhealthy diets kids are eating," Brownell said.
In the past decade, many schools have scaled back recess time or physical education classes to provide more time to prepare students for testing programs that are a key part of school funding formulas, said Dr. Vincent Ferrandino, executive director of the National Association of Elementary School Principals.
"Many of those schools that made those choices to cut back on PE classes now realize that was not a good decision in regards to their students' health," Ferrandino said.