Differences in insulin resistance in Mexican and U.S. Pima Indians with normal glucose tolerance.
BACKGROUND
Insulin resistance is a major risk factor for the development of type 2 diabetes in Pima Indians, a population with the highest prevalence of type 2 diabetes mellitus in the world. Their Mexican counterpart, living a traditional lifestyle in the mountains of Sonora, have at least 5 times less diabetes than the U.S. Pima Indians.


OBJECTIVE
We evaluated whether Mexican Pima Indians had lower insulin resistance than U.S. Pima Indians.


METHODS
We compared fasting insulin and homeostasis model assessment for insulin resistance (HOMA-IR) in 194 Mexican Pima Indians (100 females, 94 males) and 449 U.S. Pima Indians (246 females, 203 males) with normal glucose tolerance from a cross-sectional study. Adjusted differences of log-transformed outcomes (fasting insulin and HOMA-IR) between groups were evaluated using multiple linear regression models and paired t test in a matched subset.


RESULTS
Unadjusted fasting insulin and HOMA-IR were much lower in the Mexican Pima Indians than in their U.S. counterparts. After adjusting by obesity, age, and sex, mean (95% confidence interval) for fasting insulin was 6.22 (5.34-7.24) vs. 13.56 μU/ml (12.27-14.97) and for HOMA-IR 1.40 (1.20-1.64) vs. 3.07 (2.77-3.40), respectively, for Mexican Pima and U.S. Pima Indians. Results were confirmed in subset matched for age, sex, and body fat.


CONCLUSIONS
Our results indicate that Mexican Pima Indians have lower insulin resistance in comparison with their genetically related U.S. counterparts, even after controlling for differences in obesity, age, and sex. This finding underscores the importance of lifestyle factors as protecting factors against insulin resistance in individuals with a high propensity to develop diabetes.
Esparza-Romero
Julian
J
Centro de Investigación en Alimentación y Desarrollo, Hermosillo, México. julian@ciad.mx
Valencia
Mauro E
ME
Martinez
Maria Elena
ME
Ravussin
Eric
E
Schulz
Leslie O
LO
Bennett
Peter H
PH
D000328:Adult; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000208:ethnology*; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007198:Indians, North American; D007333:Insulin Resistance / Q000208:ethnology*; D008019:Life Style; D016014:Linear Models; D008297:Male; D008800:Mexico / Q000208:ethnology; D008875:Middle Aged; D014481:United States / Q000208:ethnology