Youth Fitness Linked To Diabetes Risk

Now, Medical College of Georgia researchers have found decreasing body fat and increasing cardiovascular fitness also play a major role in reducing the risks for children.

In the December issue of the Journal of Pediatrics, researchers at MCG’s Georgia Prevention Institute report that youths who are cardiovascularly fit and lean have lower fasting insulin concentrations than youths with high body fat and low cardiovascular fitness levels.

“High levels of fasting insulin implies a higher risk for type 2 diabetes and cardiovascular disease,” said Dr. Bernard Gutin, exercise physiologist and lead author of the study. “Having high insulin means the pancreas is still able to maintain control over the glucose, but it’s working harder to do so. If this process continues, the pancreas may be unable to keep up and the person gets diabetes.”

In addition to studying insulin levels, the two-year epidemiology study looked at body fat percentages and fitness levels of 278 black and white 14- to 18-year-olds. The researchers measured body fat with dual-energy X-ray absorptiometry, or DXA-scan, a more precise measure than a commonly used risk indicator called a body mass index. Where BMI calculates risk for chronic disease based on weight and height, a DXA-scan measures percentages of the body comprised of fat.

“Measuring only BMI ignores the proportion of the body made up of muscle,” said Dr. Gutin. “A person with high BMI who has large muscles is not at as much risk for diabetes as a person with the same high BMI with poorly developed muscles.”

To assess cardiovascular health, the researchers administered a treadmill test where walking became progressively more difficult as the treadmill grade increased. Those whose heart rates did not increase drastically as the grade increased were categorized as the most fit.

“We’ve known for some time that obese kids have higher insulin levels, what hasn’t been known is the relationship to cardiovascular fitness,” said Dr. Gutin. “When we study obese kids or adults, we say the high insulin might be due to obesity, but it might also be due to the lack of fitness that goes with the obesity. With this study, we’ve shown that poor fitness and high fat are related to high insulin levels.”

Study participants with the highest insulin levels had the highest percentages of body fat and the lowest levels of cardiovascular fitness, increasing their risk for type 2 diabetes and heart disease. Overall, black girls had the highest fasting insulin concentrations and white girls had the lowest. The study also showed that the harmful effects of low cardiovascular fitness and high blood pressure are greater in boys than girls.

“These data may point to one of the reasons why women prior to menopause have a lower risk of heart disease. Estrogen may have a protective effect against the deleterious effects of poor fitness and high fatness,” said Dr. Gutin.

The research, he said, is an early step in discovering how disease processes, such as type 2 diabetes, which were previously thought to be adult problems, begin in childhood.

“We are operating under the assumption that the pathophysiologic processes that lead to these diseases begin in childhood,” he said. “We want to clarify how these processes develop early in life, which will help us develop interventions to prevent the processes from continuing.

“The bottom line is both a reduction in fat and an improvement in fitness are important for reducing risk,” said Dr. Gutin. “Before this study, we knew this for adults, but not for youths. The earlier you intervene and keep the disease process from progressing, the better.”

Dr. Gutin’s collaborators include MCG exercise physiologists Zenong Yin and Paule Barbeau; pediatric endocrinologist William Hoffman; nutrition scientist Barbara Gower at the University of Alabama at Birmingham; and Matt Humphries, project coordinator.

The research was supported by the National Institutes of Health and the University of Alabama at Birmingham Clinical Nutrition Research Unit Core Laboratory.