Nondiabetic Mexican-Americans do not have reduced insulin responses relative to nondiabetic non-Hispanic whites

OBJECTIVE - To study why Mexican-Americans have a threefold increase in NIDDM relative to non-Hispanic whites. The etiology of NIDDM is still controversial, with both insulin resistance and decreased insulin secretion proposed as precursors of NIDDM. RESEARCH DESIGN AND METHODS - We examined possible ethnic differences in fasting insulin (as a marker of insulin resistance) and change in insulin-to-change in glucose ratio (Delta I-30:Delta G(30)) during the first 30 min after oral glucose ingestion (as a marker of abnormal insulin secretion) in 1,692 nondiabetic Mexican-Americans and 894 nondiabetic non-Hispanic whites from the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Fasting insulin and Delta I-30:Delta G(30) were evaluated as continuous variables. RESULTS - Mexican-Americans had increased insulin concentrations at fasting and 30, 60, and 120 min after an oral glucose load as well as an increased 0- to 30-min increment in insulin and Delta I-30:Delta G(30) relative to non-Hispanic whites. These results remained unchanged after adjustment for age, sex, obesity, body fat distribution, and glucose tolerance. CONCLUSIONS - These results suggest that increased insulin resistance rather than decreased insulin secretion is characteristic of nondiabetic Mexican-Americans, a high-risk population for NIDDM.