Higher fasting insulin but lower fasting C-peptide levels in African Americans in the US population.
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.
Harris
Maureen I
MI
National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892-5460, USA.
Cowie
Catherine C
CC
Gu
Ken
K
Francis
Mildred E
ME
Flegal
Katherine
K
Eberhardt
Mark S
MS
D000328:Adult; D001741:Black or African American; D000367:Age Factors; D000368:Aged; D002096:C-Peptide / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology; D005215:Fasting / Q000502:physiology*; D005260:Female; D006801:Humans; D015994:Incidence; D007328:Insulin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012727:Sex Characteristics; D014481:United States / Q000453:epidemiology
D002096:C-Peptide; D007328:Insulin