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Insulin resistance and excess risk of diabetes in Mexican-Americans: the San Antonio Heart Study.

CONTEXT
Mexican-Americans have more diabetes than non-Hispanic whites, but the extent to which insulin resistance and insulin secretion explain the ethnic difference is unknown.


OBJECTIVE
We analyzed selected indices of insulin resistance and secretion for both the ethnic difference and predictive discrimination.


DESIGN AND SETTING
The San Antonio Heart Study is a longitudinal population-based study with a follow-up period of 7.5 yr.


PARTICIPANTS
A total of 1540 nondiabetic individuals aged 25-64 yr were enrolled from January 1984 to December 1988.


INTERVENTIONS
Homeostasis model assessment (HOMA) of insulin resistance and secretion were estimated by available formulas (HOMA-IR and HOMA β-cell) and computer program (HOMA2S and HOMA2B). Matsuda index and insulinogenic index from 0 to 30 and 0 to 120 min (ΔI0-30/ΔG0-30 and ΔI0-120/ΔG0-120) were also calculated.


MAIN OUTCOME MEASURE
Incident diabetes was defined by the 2003 American Diabetes Association criteria.


RESULTS
Incident diabetes was in excess in Mexican-Americans [odds ratio 2.26 (95% confidence interval, 1.53-3.34)]. Matsuda index explained a larger proportion of the ethnic difference than did HOMA-IR (49.2 vs. 31.0%; P<0.001). The ethnic difference was not explained by measures of insulin secretion. Matsuda index and ΔI0-30/ΔG0-30 had a better predictive discrimination than their HOMA equivalents and ΔI0-120/ΔG0-120. HOMA estimates by the computer program offered no advantage over simple formulas for HOMA.


CONCLUSIONS
Insulin resistance accounts for a large and significant proportion of the excess risk of diabetes in Mexican-Americans. Matsuda index is better than HOMA-IR for both explaining the ethnic difference and predicting diabetes.