(HealthDay News) – Obese teenagers in the upper range of normal glucose tolerance exhibit impairments in insulin sensitivity and secretion associated with development of impaired glucose tolerance, according to a study published online Feb. 7 in Diabetes.

Cosimo Giannini, MD, from the Yale University School of Medicine in New Haven, CT, and colleagues examined insulin secretion and sensitivity in 60 obese adolescents whose two-hour post-oral glucose tolerances were within the normal range (divided into three groups: <100, 100 to 119, and 120–139 mg/dL) and in 21 obese adolescents with impaired glucose tolerance. Glucose tolerance was re-examined after two years.

The researchers found that insulin sensitivity, first-phase insulin secretion, and the disposition index decreased significantly in all three groups in the normal range, but were similar in the highest normal glucose tolerance group and the impaired glucose tolerance group. Second-phase insulin secretion was similar in all groups. The best predictors of two-hour glucose tolerance after two years were age and the disposition index.

“In obese youth classified as normal glucose tolerance but with two-hour glucose levels in the higher range, reduced β-cell function relative to insulin sensitivity has already developed, increasing the future risk of impaired glucose tolerance,” Giannini and colleagues write.

One author is an employee of Eli Lilly and Company.

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