Objective: First-degree relatives (FDR) of type 2 diabetic patients are often insulin resistant. Visceral obesity is closely linked to both insulin resistance and type 2 diabetes. We therefore hypothesized that the inheritance of an increased tendency to store fat in visceral fat depots may be a characteristic phenotypic feature in FDR contributing to their insulin resistance. Design and methods: We measured fat distribution in 20 FDR and 14 age-, gender- and body mass index (BMI)-matched controls employing dual energy X-ray absorbtiometry (DEXA)- and computed tomography (CT)-scanning. Insulin-stimulated glucose uptake (ISGU) was determined by a hyperinsulinemic clamp and maximal aerobic work capacity (VO2 max) by a bicycle ergometer test. Baseline lipolysis was measured using [3H]palmitate. The activity level of the hypothalamic-pituitary-adrenal axis was assessed as the 24 h urinary (u -cortisol/creatinine ratio. Results: All subjects had a normal oral glucose tolerance test (OGTT), but FDR were insulin resistant (ISGU: 6.64±0.48 vs 9.12±0.98 mg/kg ffm/min, P = 0.01). Despite similar BMI (25.2±0.5 vs 24.8±0.7 kg/m2, P = 0.61) and overall fat mass (26.4±1.6 vs 24.2±2.1%, P = 0.41) in FDR vs controls, the amount of visceral adipose tissue was substantially increased (65.9±-10.0 vs 40.1±11.3 cm2, P < 0.05) and VO2 max was reduced (52.2±3.1 vs 63.3±3.9 ml/kg ffm/min, P < 0.05) in FDR. Visceral adiposity was inversely correlated with ISGU (FDR: r = -0.52, P < 0.05; controls: r = -0.65, P < 0.01) and in multiple regression analysis visceral adiposity (P < 0.01), VO2 max (P < 0.001) and a family history of type 2 diabetes (P < 0.05) (r2 = 0.64) all significantly and independently contributed to the level of ISGU. Baseline palmitate appearance (145±10 vs 139±15 μmol/min, P = 0.74) and the 24 h u-cortisol/creatinine ratio ((24.9±1.3 vs 27.4±2.0)·10-6, P = 0.28) were both comparable in the two groups. Conclusion: Healthy but insulin-resistant FDR have enhanced visceral obesity and reduced VO2 max compared with people without a family history of diabetes, despite similar BMI and overall fat mass. Both the visceral adiposity and reduced aerobic fitness are strongly associated with and may contribute to their insulin resistance.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism