title: Abdominal obesity predicts declining insulin sensitivity in non-obese normoglycaemics: the Insulin Resistance Atherosclerosis Study (IRAS).
abstract: OBJECTIVE
  Cross-sectional studies have demonstrated a relationship between obesity and insulin sensitivity (S(I)); however, there is a lack of evidence from longitudinal studies.
  
  
  METHODS
  The Insulin Resistance Atherosclerosis Study (IRAS) estimated S(I) (x10(-4)/min.microU/ml) directly using a frequently sampled intravenous glucose tolerance test with minimal model analysis in 504 normoglycaemic subjects. Partial correlation coefficients (r) were calculated to compare the relationship of change in S(I) from baseline to 5 years later (DeltaS(I)) with baseline waist circumference (waist) as a measure of abdominal obesity and body mass index (BMI) as a measure of overall obesity. Mean DeltaS(I) was -1.06 (SD = 1.85).
  
  
  RESULTS
  Higher baseline waist (r = -0.16; p = 0.0005), but not BMI (r = -0.005; p = 0.91), was associated with (-) DeltaS(I) in models including sex, ethnicity, clinical centre and baseline S(I), BMI, waist, age and physical activity. The waist-DeltaS(I) relationship differed across the levels of baseline BMI, being significant only in normal weight (r = -0.21) and overweight subjects (r = -0.16), but not in obese subjects. DeltaS(I) was correlated with a 5-year change in either obesity measure (Deltawaist: r = -0.22 and DeltaBMI: r = -0.20; p = 0.0001).
  
  
  CONCLUSIONS
  Among non-diabetics, waist circumference was a strong predictor of declining S(I) among lean subjects, a modest predictor among overweight subjects, but was not predictive among obese individuals. Waist circumference should be considered, in addition to BMI, when identifying individuals at high risk of diabetes or the insulin resistance syndrome.
authors.affiliation: Kaiser Permanente, Division of Research, Northern California Region, Oakland, CA, USA. andy.j.karter@kp.org
authors.forename: A J
authors.initials: AJ
authors.lastname: Karter
authors.forename: R B
authors.initials: RB
authors.lastname: D'Agostino
authors.forename: E J
authors.initials: EJ
authors.lastname: Mayer-Davis
authors.forename: L E
authors.initials: LE
authors.lastname: Wagenknecht
authors.forename: A J G
authors.initials: AJ
authors.lastname: Hanley
authors.forename: R F
authors.initials: RF
authors.lastname: Hamman
authors.forename: R
authors.initials: R
authors.lastname: Bergman
authors.forename: M F
authors.initials: MF
authors.lastname: Saad
authors.forename: S M
authors.initials: SM
authors.lastname: Haffner
mesh_terms: D000005:Abdomen; D000328:Adult; D001741:Black or African American; D000368:Aged; D000375:Aging; D001161:Arteriosclerosis / Q000208:ethnology / Q000378:metabolism*; D001824:Body Constitution; D015992:Body Mass Index; D005260:Female; D005500:Follow-Up Studies; D006630:Hispanic or Latino; D006801:Humans; D007333:Insulin Resistance; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000208:ethnology / Q000378:metabolism*; D011446:Prospective Studies; D044465:White People