NEW YORK (Reuters Health) - For the first time, researchers have found that one in four extremely obese children under the age of 10 and one in five obese adolescents under the age of 18 in the US have a condition known as impaired glucose tolerance--a precursor to type 2 diabetes.

The disease--formerly known as adult-onset diabetes--increases the risk of heart disease, kidney failure, blindness and limb amputations. The longer people live with type 2 diabetes, the more likely they are to have devastating medical complications.

The increase in obesity is probably the culprit behind the childhood cases. People who are overweight are more likely to lose their sensitivity to the effects of insulin, the blood glucose (sugar)-regulating hormone. When the body ignores the hormone, blood glucose rises and, over time, can cause serious medical complications.

The good news is that changes in diet and increased exercise often can reverse impaired glucose tolerance, which, in turn, can prevent or delay the development of type 2 diabetes.

Since many studies have shown a correlation between obesity and type 2 diabetes, Dr. Ranjana Sinha of Yale University in New Haven, Connecticut, and colleagues set out to determine if there was a similar association between obesity and impaired glucose tolerance.

To investigate, the researchers measured blood glucose levels in 55 children aged 4 to 10 years and 112 adolescents aged 11 to 18. All of the participants were obese and were white, black or Hispanic, according to the report published in the March 14th issue of The New England Journal of Medicine. The youngsters had all been referred to a weight-loss clinic, and were heavier than 95% of children in their age group.

The investigators identified impaired glucose tolerance in 25% of the children and 21% of the adolescents. Silent type 2 diabetes was found in 4% of the obese adolescents--meaning that the patients were not aware they had diabetes.

"Impaired glucose tolerance is highly prevalent among children and adolescents with severe obesity, irrespective of ethnic group," Sinha and colleagues write.

Children most at risk of being diagnosed with impaired glucose tolerance had insulin resistance and high levels of insulin in their blood, the report indicates.

"The degree of obesity was not found to be a significant risk factor (for impaired glucose tolerance), possibly because the majority of our subjects were severely obese," they add. "The effects of obesity on the deterioration of glucose tolerance are most likely mediated by its metabolic complications--particularly insulin resistance and hyperinsulinemia (the presence of excess insulin in the blood)."

"Although it is possible to treat obesity, it is extremely difficult and requires both extensive resources and a very highly motivated child and family," writes Dr. Albert P. Rocchini of the University of Michigan in Ann Arbor, in an accompanying editorial. "Even with successful weight loss, the rate of relapse is high.

"I believe that a more effective strategy is to identify those obese children who are at high risk for diabetes and to target them for intensive weight-loss treatment," he added. Glucose tolerance testing may be an "excellent" way to identify those children most at risk for diabetes, Rocchini said.

SOURCE: The New England Journal of Medicine 2002;346:802-810, 854-855.

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