Was the historic contribution of Spain to the Mexican gene pool partially responsible for the higher prevalence of type 2 diabetes in Mexican-origin populations? The Spanish Insulin Resistance Study Group, the San Antonio Heart Study, and the Mexico City Diabetes Study

OBJECTIVE - Mexican-American populations in San Antonio, Texas (SA-MA) and Mexico have a higher prevalence of type 2 diabetes than non-Hispanic whites in San Antonio (SA-NHW). However, the higher prevalence of type 2 diabetes in Mexican-origin populations might be related, in part, not to Native Ame rican genetic admixture but to Spanish genetic admixture. RESEARCH DESIGN AND METHODS - Four population-based epidemiological surveys conducted with Mexican-origin and European-origin samples provided data re levant to this question. in all four surveys, type 2 diabetes was defined a s fasting plasma glucose greater than or equal to7.0 mmol/l or 2-h glucose greater than or equal to 11.1 mmol/l or use of antidiabetic agents. RESULTS - A comparison of the two Mexican-origin populations showed that th e age- and sex-adjusted prevalence of type 2 diabetes was lower in Mexico t han in SA-MA (15.1 vs. 17.9%, P = 0.032). Between the two European-origin p opulations, the prevalence of type 2 diabetes was lower in SA-NHW than in S pain (6.2 vs. 9.1%, P < 0.0001), but differences were attenuated by adjustm ent BMI or after stratification by education. In logistic regression analys es, type 2 diabetes was associated with Mexican ethnic origin after adjusti ng for age, education, BMI, and waist-to-hip ratio. CONCLUSIONS - The prevalence of type 2 diabetes in Spain was intermediate b etween that in Mexican-origin populations and SA-NHW. Although the higher d egree of Native American admixture is a major contributor to the higher rat es of type 2 diabetes, we cannot completely rule out a partial contribution of Spanish admixture to diabetes susceptibility among Mexican-origin popul ations.