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 I30:delta G30) during the first 30 min after oral glucose ingestion (as a marker of abnormal whites from the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Fasting insulin and delta I30:delta G30 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 I30:delta G30 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.