Continuation of growth hormone therapy versus placebo in transition-phase patients with growth hormone deficiency: impact on body composition, insulin sensitivity, and thyroid function.

In a placebo-controlled, parallel study of 18 patients with a mean age of 20 years who had confirmed growth hormone (GH) deficiency, we evaluated body composition, insulin sensitivity, and glucose turnover at baseline (when all were receiving GH replacement); after 12 months of continued GH therapy or placebo; and after a 12-month open phase of GH therapy. In the placebo group, insulin sensitivity and fat mass increased and lipid oxidation decreased, whereas glucose oxidation increased (p <0.05). During the open phase, insulin sensitivity decreased in the former placebo group although body fat decreased and fat-free mass increased. Throughout the study, most hormonal and metabolic parameters remained unchanged in those receiving continued GH therapy. These results indicate that: 1-year discontinuation of GH therapy induces fat accumulation in GH-deficient adolescents without compromising insulin sensitivity; the beneficial effects of continued GH treatment on body composition do not fully counterbalance its direct insulin antagonistic effects; and GH replacement has favorable effects on iodothyronine metabolism and quality of life.