Visceral obesity, impaired glucose tolerance, metabolic syndrome, and growth hormone therapy

Overweight adults with impaired glucose tolerance have a 5-10% risk of developing diabetes per year, and insulin resistance is an important cause of progression to diabetes in these individuals. Weight loss has been shown to improve insulin sensitivity and prevent or delay progression to diabetes. According to recent studies, the improvement in insulin sensitivity that occurs with weight loss is closely linked to the reduction of visceral adipose tissue (VAT), the collection of intra-abdominal adipose depots that includes omental and intrahepatic fat. After controlling for BMI, whole body fat, and subcutaneous fat, only VAT is an independent predictor of endogenous insulin sensitivity and glucose tolerance before or after weight loss. This, in turn, suggests that reducing VAT is crucial to improving insulin sensitivity and preventing diabetes in high-risk individuals. Recombinant human growth hormone (GH) is a lipolytic drug that reduces total body, abdominal, and visceral fat in growth hormone-deficient (GHD) adults. Several studies have reported substantial reductions in VAT following GH treatment in this population. Like GHD adults, abdominally obese individuals have increased VAT, insulin resistance, and growth hormone levels that are below normal during continuous 24-h monitoring. These similarities have prompted a number of recent investigations in abdominally obese adults that reported significant reductions in truncal and visceral fat and an improvement in insulin sensitivity following prolonged GH administration. However, other studies have shown that insulin resistance and glucose concentrations transiently worsen during the first few weeks of GH treatment and that these deleterious effects can persist even after VAT reduction has occurred. Prior studies involving GH treatment were generally limited to adults who were normoglycemic at baseline. Less is known about the effects of GH in adults with impaired glucose tolerance or diabetes. The effects of GH used in conjunction with insulin sensitizers on glycemic control and VAT in patients with impaired glucose tolerance will be reviewed. (c) 2006 Elsevier Ltd. All rights reserved.