Visceral adiposity and the risk of impaired glucose tolerance: a prospective study among Japanese Americans

OBJECTIVE: Greater visceral adiposity, higher insulin resistance, and impaired insulin secretion increase the risk of type 2 diabetes. Whether visceral adiposity increases risk of impaired glucose tolerance (IGT) independent of other adipose depots, insulin resistance, and insulin secretion is not known. RESEARCH DESIGN AND METHODS: Study subjects included 128 Japanese Americans with normal glucose tolerance at entry. Baseline variables included plasma glucose and insulin measured after an overnight fast and during a 75-g oral glucose tolerance test, fat areas by computed tomography, insulin secretion (incremental insulin response [IIR] [30 min insulin - fasting insulin]/30 min glucose), and insulin resistance index (homeostasis model assessment for insulin resistance [HOMA-IR]). RESULTS: During the 10- to 11-year follow-up period, we confirmed 57 cases of IGT. Significant predictors of IGT included intra-abdominal fat area (IAFA) (odds ratio [OR] for a 1 SD increase 3.82, 95% CI 1.63-8.94 at a fasting plasma glucose [FPG] level of 4.5 mmol/l), HOMA-IR (2.41, 1.15-5.04), IIR (0.30, 0.13-0.69 at an FPG level of 4.5 mmol/l), the interactions of IAFA by FPG (P = 0.003), and IIR by FPG (P = 0.030) after adjusting for age, sex, FPG, and BMI. The multiple-adjusted OR of IAFA increased and that of IIR decreased as FPG level decreased because of these interactions. Even after adjustment for total fat area, total subcutaneous fat area, or abdominal subcutaneous fat area, all of these associations remained a significant predictor of IGT incidence. CONCLUSIONS: Greater visceral adiposity increases the risk of IGT independent of insulin resistance, insulin secretion, and other adipose depots in Japanese Americans.