Few data exist on predictors of non-insulin-dependent (type II) diabetes mellitus. We examined body mass index (BMI), ratio of subscapular-to-triceps skin fold (centrality index), and fasting glucose and insulin concentrations as predictors of decompensation to type II diabetes in Mexican Americans, a population at high risk for this disorder. Twenty-eight of 474 initially nondiabetic Mexican Americans developed type II diabetes after 8 yr of follow-up. Converters to diabetes were older and had higher BMIs, centrality indices, and fasting glucose and insulin concentrations than nonconverters. Subjects in the highest quartile of the insulin distribution had 6.6 times the risk of developing type II diabetes as subjects in the remaining three quartiles combined (95% confidence interval [CI] = 3.14–13.7). In multivariate analysis, fasting glucose (odds ratio [OR] = 5.80, 95% CI = 2.57–13.1) and insulin (OR = 3.12, 95% CI = 1.36–7.14) remained significantly related to conversion to diabetes. However, BMI and centrality index, which were significantly related to conversion in the univariate analysis, were no longer significant in the multivariate analysis once glucose and insulin concentrations were taken into consideration, suggesting that the effect of these variables may be mediated by insulin resistance. Nearly half of the incident cases developed in a subset of the population who were simultaneously in the highest quartile of both fasting insulin and glucose concentrations (population-attributable risk 44.2%). Our results support the insulin resistance/pancreatic exhaustion theory of type II diabetes.

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