BACKGROUND: Patients with adult-onset growth hormone deficiency have reduced bone density and increased fat mass. Growth hormone at high doses may decrease body fat in these patients, but the effects of growth hormone at more physiologic doses on bone density and body composition have not been convincingly shown.

OBJECTIVE: To determine whether long-term growth hormone at a dose adjusted to maintain normal insulin-like growth factor 1 (IGF-1) levels has clinical effects in patients with adult-onset growth hormone deficiency.

DESIGN: Randomized, placebo-controlled study.

SETTING: Tertiary referral center.

PATIENTS: 32 men with adult-onset growth hormone deficiency.

INTERVENTION: Growth hormone (initial daily dose, 10 micrograms/kg of body weight) or placebo for 18 months. The growth hormone dose was reduced by 25% if IGF-1 levels were elevated.

MEASUREMENTS: Body composition and bone mineral density of the lumbar spine, femoral neck, and proximal radius were measured by dual energy x-ray absorptiometry at 6-month intervals. Markers of bone turnover were also measured during the first 12 months of the study.

RESULTS: Growth hormone increased bone mineral density in the lumbar spine by a mean (+/- SD) of 5.1% +/- 4.1% and bone mineral density in the femoral neck by 2.4% +/- 3.5%. In the growth hormone group, significant increases were seen in the following markers of bone turnover: osteocalcin (4.4 +/- 3.6 mg/L to 7.2 +/- 4.6 mg/L) and urinary pyridinoline (39.0 +/- 19.8 nmol/mmol of creatinine to 55.7 +/- 25.5 nmol/mmol of creatinine) and deoxypyridinoline (8.4 +/- 7.1 nmol/mmol of creatinine to 14.9 +/- 9.4 nmol/mmol of creatinine). Percentage of body fat in the growth hormone group decreased (from 31.9% +/- 6.5% to 28.3% +/- 7.0%), and lean body mass increased (from 59.0 +/- 8.5 kg to 61.5 +/- 6.9 kg). These changes were significant compared with corresponding changes in the placebo group (P < 0.01 for all comparisons).

CONCLUSIONS: Growth hormone administered to men with adult-onset growth hormone deficiency at a dose adjusted according to serum IGF-1 levels increases bone density and stimulates bone turnover, decreases body fat and increases lean mass, and is associated with a low incidence of side effects.