Limited value of the homeostasis model assessment to predict insulin resistance in older men with impaired glucose tolerance

OBJECTIVE- Insulin resistance (IR) in older individuals is associated with risk factors for coronary artery disease. The glucose clamp measures IR dir ectly but the homeostasis model assessment (HOMA) of IR, referred to here a s HOMA-IR, is based on fasting glucose and insulin and is less invasive and labor intensive. This method requires validation in the elderly. RESEARCH DESIGN AND METHODS- We assessed the validity of HOMA-IR as an inde x of IR by comparing it to glucose infusion rates (GIRs) measured by a gluc ose clamp (600 pmol . m(-2) . min(-1)) in 45 obese men (61 +/- 8 years of a ge, mean +/- SD) with normal glucose tolerance (NGT) (n = 21) or impaired g lucose tolerance (IGT) (n = 24). We also evaluated relationships between bo dy composition, exercise capacity, and IR. RESULTS- Subjects with NGT had lower BMI (28 +/- 3 vs. 31 +/- 3 kg/m(2)), w aist circumference (97 +/- 9 vs. 105 +/- 9 cm), waist-to-hip ratio (WHR) (0 .93 +/- 0.06 vs. 0.97 +/- 0.05), and percent body fat (25 +/- 6 vs. 30 +/- 6) than subjects with IGT. Subjects with NGT also had lower areas above bas al during the 2-h oral glucose tolerance lest for glucose (274 +/- 95 vs. 4 19 +/- 124 mmol . min/l) and insulin (38,142 +/- 18,206 vs. 58,383 +/- 34,4 08 pmol . min/l) and lower HOMA-IR values (2.2 +/- 0.8 vs. 4.2 +/- 2.6) tha n subjects with IGT. GIR (mu mol . kg(-1) FFM . min(-1)) was higher in subj ects with NGT than in subjects with IGT (53 +/- 11 vs. 43 +/- 14). HOMA-IR correlated with GIR in subjects with NGT (r = -0.59), but not in subjects w ith IGT (r = -0.13). GIR correlated with Vo(2max) in subjects with NGT (r = 0.58) and IGT (r = 0.42), but with WHR only in subjects with NGT (r = -0.5 3). HOMA-IR correlated with Vo(2max) (r = -0.57) and waist circumference (r = 0.54) in subjects with NGT, but with percent body fat in subjects with I GT (r = 0.54). CONCLUSIONS- These findings indicate that HOMA-IR should not be used as an index of IR in older individuals who may be at risk for IGT, and suggest th at lifestyle changes that increase Vo(2max) and decrease body fat may reduc e IR in older people.