RELATION OF OBESITY TO INSULIN-SECRETION AND CLEARANCE IN ADOLESCENTS- THE BOGALUSA HEART-STUDY

OBJECTIVE: Earlier we found elevated insulin levels in obese children and adolescents. The present study examines whether alterations in ins ulin secretion and/or clearance contribute to hyperinsulinemia in obes e adolescents. METHODS: Easting circulating insulin and C-peptide conc entrations were examined in 1157 adolescents, aged 11-18 y, from a bir acial (black/white) community. In this epidemiologic study, plasma C-p eptide was used as a noninvasive measure of insulin secretion by beta cells, C-peptide to insulin ratio as an indicator of hepatic insulin e xtraction, and insulin to glucose ratio as a measure of insulin sensit ivity. Body mass index (BMI) was used as an index of obesity, since it is strongly associated with insulin levels and the C-peptide to insul in ratio more so than with measures of skinfolds and percent body fatn ess. RESULTS: Obese individuals (BMI > 90th P) had higher levels of pl asma insulin (23.7 mu/ml vs 11.7 mu/ml), C-peptide (2.7 ng/ml vs 1.7 n g/ml), and insulin to glucose ratio (0.29 vs 0.15), and lower C-peptid e to insulin ratio (0.13 vs 0.16) than non-obese adolescents (all P < 0.001). Elevated C-peptide and decreased C-peptide to insulin ratio we re noted in subjects with both obesity and hyperinsulinemia (insulin > 90th P) versus those without these conditions (P < 0.001). Individual s with obesity and low insulin clearance (C-peptide/insulin < 10th P) had 18-fold higher prevalence of hyperinsulinemia versus those without these conditions. Although black adolescents, despite their lower per cent body fat, had higher insulin and lower C-peptide and C-peptide to insulin ratio than their white counterparts, BMI related positively t o insulin and C-peptide, and inversely with C-peptide to insulin ratio in both races. CONCLUSION: These data suggest that both increased ins ulin secretion and decreased insulin clearance contribute to hyperinsu linema in obese adolescents.