Insulin resistance drives excess diabetes risk in Mexican Americans
MedWire News: The excess risk for diabetes faced by Mexican Americans is largely driven by insulin resistance, an analysis of the San Antonio Heart Study indicates.
The San Antonio Heart Study is a longitudinal, epidemiologic study designed to evaluate Type 2 diabetes and cardiovascular disease among Mexican Americans and non-Hispanic White individuals living in an urban area in Texas, USA.
In this analysis, Carlos Lorenzo (University of Texas Health Science Center, San Antonio) and team hypothesized that differences in insulin handling - either insulin secretion, resistance, or both - might account for the greater burden of diabetes in Mexican Americans as opposed to non-Hispanic Whites.
They obtained information on 1540 study participants who were free of diabetes and aged between 25 and 64 years at enrolment. At the 7.5-year follow-up examination, 144 (14.0%) of 1030 Mexican Americans and 35 (6.9%) of 510 non-Hispanic Whites had developed diabetes.
Among participants with newly diagnosed diabetes, clinical and metabolic characteristics were similar between the two racial/ethnic groups. However, in both groups, baseline indices of insulin resistance and sensitivity predicted the development of diabetes.
Specifically, odds ratios per 1-standard deviation increase were 2.79, 0.38, and 0.34 for insulin resistance measured by homeostasis model assessment (HOMA-IR), 0.38 for insulin resistance estimated with a computer program (HOMA2S), and 0.34 for a surrogate of insulin sensitivity directly measured by euglycemic-hyperinsulinemic clamp (Matsuda index).
Analysis of receiver operating characteristic curves showed that the Matsuda index was a strong predictor for incident diabetes, with an area under the curve (AUC) of 0.766.
Neither HOMA-IR nor computer estimates outperformed Matsuda index. However, in models with Matsuda index as a covariate, the best predictor for incident diabetes was the insulogenic index, with an AUC of 0.850.
The Matsuda index also explained a greater proportion of the ethnic difference in diabetes incidence than did HOMA-IR, at 49.2 versus 31.0%. By contrast, differences in insulin secretion did not contribute to the greater burden of diabetes in Mexican Americans.
Finally, the use of computer programs to estimate insulin resistance and secretion offered no advantages over simple formulas for HOMA, Carlos and co-authors remark.
They conclude: "Insulin resistance may account for a large part of the excess risk of Type 2 diabetes in Mexican Americans, whereas insulin secretion… explains little of the ethnic difference.
"Further studies are needed to conduct similar analyses in other high-risk racial and ethnic groups such as South Asians and subjects of African descent."
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By Joanna Lyford