Racial (black-white) differences in insulin secretion and clearance in adolescents : The Bogalusa Heart Study

Objective. Earlier we found black-white contrast in insulin levels in adolescents. The purpose of this study is to assess whether this difference is attributable to alterations in insulin secretion and/or clearance. Methods. Fasting circulating insulin and C-peptide concentrations were examined in 1157 adolescents aged 11 to 18 years from a biracial community. Fasting plasma C-peptide, C-peptide to insulin ratio, and glucose to insulin ratio were used as indices of insulin secretion, hepatic insulin clearance, and insulin sensitivity, respectively. Results. After adjusting several covariates (age, sexual maturation, and obesity), black adolescents had higher insulin levels (14.99 vs 12.66 μU/mL in girls). However, they had lower C-peptide levels than their white counterparts, indicating lower insulin secretion by pancreatic beta cells in black adolescents. Moreover, black adolescents had lower levels of C-peptide to insulin ratio than white adolescents (0.14 vs 0.17), suggesting reduced hepatic insulin clearance in black adolescents. In addition, significantly lower levels of glucose to insulin ratio in black girls suggest a reduced insulin sensitivity in this group. Further, differences in insulin levels between white and black girls disappeared after adjusting for differences in C-peptide to insulin ratio. Conclusion. These data suggest that elevated insulin levels observed in black adolescents, especially in black girls, may be attributed to their decreased hepatic insulin clearance, not hypersecretion of insulin.