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Exercise improves thinking, reduces diabetes risk in overweight children

October 23, 2007

Just three months of daily, vigorous physical activity in overweight children improves their thinking and reduces their diabetes risk, researchers say.

Studies of about 200 overweight, inactive children ages 7-11 also showed that a regular exercise program reduces body fat and improves bone density.

"Is exercise a magic wand that turns them into lean, healthy kids? No. They are still overweight but less so, with less fat, a healthier metabolism and an improved ability to handle life," says Dr. Catherine Davis, clinical health psychologist at the Medical College of Georgia and lead investigator.

All study participants learned about healthy nutrition and the benefits of physical activity; one-third also exercised 20 minutes after school and another third exercised for 40 minutes. Children played hard, with running games, hula hoops and jump ropes, raising their heart rates to 79 percent of maximum, which is considered vigorous.

"Aerobic exercise training showed dose-response benefits on executive function (decision-making) and possibly math achievement, in overweight children," researchers write in an abstract being presented during The Obesity Society's Annual Scientific Meeting Oct. 20-24 in New Orleans. "Regular exercise may be a simple, important method of enhancing children's cognitive and academic development. These results may persuade educators to implement vigorous physical activity curricula during a childhood obesity epidemic."

Functional magnetic resonance imaging studies, which show the brain at work, were performed on a percentage of children in each group and found those who exercised had different patterns of brain activity during an executive function task.

"Look what good it does when they exercise," says Dr. Davis. "This is an important public health issue we need to look at as a nation to help our children learn and keep them well."

Unprecedented obesity and inactivity rates in America's children are impacting health, including dramatic increases in the incidence of type 2 diabetes, a disease formerly known as adult-onset diabetes. Overweight children also have slightly lower school achievement, on average.

"We hope these findings will help persuade policymakers, schools and communities that time spent being physically active enhances, rather than detracts, from learning," says Dr. Davis.

"There have been several studies that have shown that exercise produces kind of a selective effect, particularly with older adults, in cognitive tasks that require regulation of behaviors," says Dr. Phillip D. Tomporowski, experimental psychologist at the University of Georgia and a key collaborator.

For this study, researchers gave the children tests that look at their decision-making processes. In the first such studies in children, the researchers found small to moderate improvements in children who exercised as well as a hint of increased math achievement.

"We have a number of studies conducted with animals that examined what influence physical activity has on blood flow, metabolic activity, brain function, glucose regulation, and they all demonstrate the same theme: that physical activity done on a regular basis has a protective effect," says Dr. Tomporowski. "It doesn't take too much to make the leap that it might influence developing children as well."

Looking at the children's insulin resistance, a precursor of type 2 diabetes in which it takes more insulin to convert glucose into energy, researchers found levels dropped 15 percent in the 20-minute exercise group and 21 percent in the 40-minute group. The control group stayed about the same.

"Increasing volume of regular aerobic exercise shows increased benefits on insulin resistance in overweight children, indicating reduced risk of type 2 diabetes, regardless of sex or race," they write.

"We also know that if you stop exercising, you lose all the benefits," adds Dr. Davis. "Exercise works if you do it."

Adult studies have yielded comparable findings regarding exercise's impact on insulin resistance and cognition.

The researchers tested oral glucose tolerance, measuring insulin response after children drank a small amount of glucose, before and after the studies. "Once your glucose levels start to rise, it's called impaired glucose tolerance and that is a precursor of diabetes. It's called pre-diabetes now," says Dr. Davis, noting that overweight children typically have higher insulin resistance than their leaner peers. Insulin resistance is an early sign of diabetes risk that appears before glucose levels start to rise. Growth associated with puberty can temporarily increase insulin resistance, Dr. Davis notes, so because some of the children were beginning puberty, they made adjustments for the level of sex hormones.

DEXA scanning, which uses a small amount of radiation to quantify bone, tissue and fat, was used to accurately assess body composition. Executive function was measured using the Cognitive Assessment System and math skills using the Woodcock Johnson Test of Achievement III.

"If physical education were ideal, which it's not - it's not daily and it's not active - then children could achieve this within the school day," Dr. Davis says, pointing to benefits derived by children exercising just 20 minutes a day. "We are not there. To achieve maximum benefit, we were able to show it will take more than PE."

The researchers are submitting grants that will enable further studies.

The studies were funded by the National Institute of Health.

Medical College of Georgia