This study examined insulin sensitivity at each Tanner (T) stage of puberty in normal children to determine the natural history of insulin resistance in this age group. Participants were randomly selected from a cohort of 12,024 5th-8th grade public school students. Data represent cross-sectional evaluation of the first 318 participants (172 boys, 146 girls). Insulin sensitivity (M, mg/kg/min) was determined by the euglycemic insulin clamp method in which insulin was infused at a rate of 1mU/kg/min for 3h. A variable infusion of 20% dextrose maintained the serum glucose level at 100 mg/dl. At all T stages, M was lower in girls than boys. Insulin sensitivity decreased through the early stages of puberty in both sexes and improved after T3 in girls while remaining relatively constant after T3 in boys. BMI was inversely proportional to M, and was the strongest predictor of M at all T stages in both sexes. For a given BMI, however, M was greater in T5 than T1 in both girls and boys, probably reflecting increased muscle mass with maturity.

These data confirm the inverse relationship between BMI and M in children, and in addition, show that: 1) M is lower in girls than in boys at all Tanner stages, and 2), while M is related to BMI at all T stages, this relationship is exaggerated in the early stages of puberty in girls and in late puberty in boys. This suggests that adiposity is not the only factor influencing insulin resistance during puberty. Table

Table 1 No caption available.
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