The Homeostasis Model in the San Antonio Heart Study

OBJECTIVE: Both insulin resistance and decreased insulin secretion have been shown to predict the development of NIDDM. However, methods to assess insulin sensitivity and secretion are complicated and expensive to apply in epidemiological studies. The homeostasis model assessment (HOMA) has been suggested as a method to assess insulin resistance and secretion from the fasting glucose and insulin concentrations. However, this method has not been extensively evaluated, particularly in different ethnic groups. RESEARCH DESIGN AND METHODS: We applied the HOMA model to cross-sectional analyses of the San Antonio Heart Study (n = 2,465). RESULTS: HOMA insulin resistance (IR) was very strongly correlated with fasting insulin (r = 0.98) and HOMA beta-cell function (beta-cell) was moderately correlated with the 30-min increment in insulin concentration over the 30-min increment in glucose concentration (delta I30/delta G30) in an oral glucose tolerance test (OGTT) (r = 0.44). NIDDM was characterized by both high HOMA IR and low HOMA beta-cell function. In Mexican-Americans, HOMA IR in NIDDM subjects was 9.5 compared with 2.7 in normal glucose tolerance (NGT) subjects. In contrast, HOMA beta-cell function showed only small differences in Mexican-Americans (176 NIDDM; 257 NGT). However, the delta I30/delta G30 (pmol/mmol) showed much larger differences (75 NIDDM; 268 NGT). When modeled separately, impaired glucose tolerance (IGT) was characterized by high HOMA IR and high HOMA beta-cell function. However, when analyzed in the same regression model, high HOMA IR and low HOMA beta-cell function characterized subjects with IGT. These results were similar in both ethnic groups. Mexican-Americans had increased insulin resistance (as judged by both HOMA IR and fasting insulin) and insulin secretion (by HOMA beta-cell and delta I30/delta G30) relative to non-Hispanic whites. CONCLUSIONS: We conclude that HOMA provides a useful model to assess insulin resistance and beta-cell function in epidemiological studies in which only fasting samples are available and that, further, it is critical to take into account the degree of insulin resistance in assessing insulin secretion by the HOMA model.