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 (ΔI_0–30/ΔG_0–30 and ΔI_0–120/ΔG_0–120) 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 ΔI_0–30/ΔG_0–30 had a better predictive discrimination than their HOMA equivalents and ΔI_0–120/ΔG_0–120. 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.