title: Insulin resistance, beta-cell dysfunction, and conversion to type 2 diabetes in a multiethnic population: the Insulin Resistance Atherosclerosis Study.
abstract: OBJECTIVE
  Insulin resistance and beta-cell function are major predictors of type 2 diabetes, but studies using direct methods of insulin resistance and secretion are few and relatively small. Furthermore, the strength of these associations has not been tested in different ethnic groups and various states of glucose tolerance, family history of diabetes, and obesity.
  
  
  METHODS
  Predictors of incident diabetes were evaluated in Hispanic, non-Hispanic white, and African American participants in the Insulin Resistance Atherosclerosis Study (aged 40-69 years). In 557 participants with normal glucose tolerance and 269 with impaired glucose tolerance (IGT), insulin sensitivity (insulin sensitivity index [S(I)]) and first-phase insulin secretion (acute insulin response [AIR]) were directly measured using the frequently sampled intravenous glucose tolerance test.
  
  
  RESULTS
  At the 5-year follow-up examination, 128 (15.5%) individuals had developed diabetes. Both S(I) (odds ratio x 1 SD 0.50 [95% CI 0.37-0.68]) and AIR (0.51 [0.40-0.65]) were independent predictors of incident diabetes even after adjustment for age, sex, ethnicity, center, IGT, family history of diabetes, and BMI. The strength of the relation of S(I) and AIR to incident diabetes was not significantly affected by potential interactions of age, sex, ethnicity, glucose tolerance, BMI, or family history of diabetes (P > or = 0.15).
  
  
  CONCLUSIONS
  Both insulin sensitivity and beta-cell function predict conversion to diabetes in different ethnic groups and various states of glucose tolerance, family history of diabetes, and obesity. The prevention of type 2 diabetes should focus on interventions that improve both insulin resistance and insulin secretion.
authors.affiliation: Division of Clinical Epidemiology, University of TexasHealth Science Center, San Antonio, Texas, USA. lorenzo@uthscsa.edu
authors.forename: Carlos
authors.initials: C
authors.lastname: Lorenzo
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Wagenknecht
authors.forename: Ralph B
authors.initials: RB
authors.lastname: D'Agostino
authors.forename: Marian J
authors.initials: MJ
authors.lastname: Rewers
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Karter
authors.forename: Steven M
authors.initials: SM
authors.lastname: Haffner
mesh_terms: D000328:Adult; D001741:Black or African American; D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology* / Q000208:ethnology / Q000209:etiology* / Q000517:prevention & control; D005260:Female; D018149:Glucose Intolerance / Q000503:physiopathology; D006630:Hispanic or Latino; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000473:pathology*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D044465:White People