Higher fasting insulin but lower fasting C-peptide levels in African Americans in the US population

Diabetes Metab Res Rev. Mar-Apr 2002;18(2):149-55. doi: 10.1002/dmrr.273.

Abstract

Background: Fasting serum insulin and fasting serum C-peptide are risk factors for developing type 2 diabetes. Because of the higher incidence of type 2 diabetes in African Americans and Hispanic Americans, it is likely that these groups may differ from non-Hispanic whites in their levels of insulin and C-peptide.

Methods: We analyzed data from a nationally representative sample of adults in the US population for whom sociodemographic, clinical, and laboratory information were obtained. The data were used to describe distributions of fasting insulin and fasting C-peptide in non-Hispanic white, non-Hispanic black, and Mexican American men and women aged >or=20 years without a medical history of diabetes.

Results: Among men, Mexican Americans had higher insulin values than non-Hispanic whites and blacks. Among women, both Mexican Americans and blacks had higher insulin values than whites. For C-peptide, differences by sex and race-ethnicity paralleled those seen for fasting insulin with the exception that black men had significantly lower C-peptide values than whites and Mexican Americans. After adjustment for age, fasting plasma glucose (FPG), body mass index (BMI), and waist-to-hip ratio (WHR), the higher levels for insulin in blacks and Mexican Americans remained; both black men and women had significantly lower C-peptide values than whites and Mexican Americans. The molar ratio of fasting C-peptide to fasting insulin was similar for men and women in each race-ethnic group. However, blacks had substantially lower ratios than whites and Mexican Americans.

Conclusions: We found wide variations in fasting insulin and fasting C-peptide levels by race and ethnicity in US adults that were not explained by confounding factors, primarily measures of obesity. Most notably, the higher fasting insulin and lower fasting C-peptide levels in blacks implies that there is a derangement in insulin clearance and an impairment in beta-cell function in blacks compared with whites and Mexican Americans.

MeSH terms

  • Adult
  • African Americans*
  • Age Factors
  • Aged
  • C-Peptide / blood*
  • Diabetes Mellitus, Type 2 / epidemiology
  • Fasting / physiology*
  • Female
  • Humans
  • Incidence
  • Insulin / blood*
  • Male
  • Middle Aged
  • Risk Factors
  • Sex Characteristics
  • United States / epidemiology

Substances

  • C-Peptide
  • Insulin