CHICAGO – Six months of growth hormone therapy significantly increased bone formation, vitamin D, and thigh muscle mass while decreasing abdominal fat in a study of women with abdominal obesity.
The randomized, double-blind, placebo-controlled trial was the first to explore the relationship between growth hormone levels and bone density in obese but otherwise healthy premenopausal women, Dr. Miriam A. Bredella of Massachusetts General Hospital and Harvard Medical School, Boston, said in a press briefing at the annual meeting of the Radiological Society of North America.
Dr. Miriam A. Bredella
The study builds on work presented by Dr. Bredella at last year’s RSNA meeting showing an association between abdominal obesity and low bone mineral density in women. That study was the first to implicate abdominal fat as a risk factor for osteoporosis.
The study challenged previous research findings suggesting that increased weight protects against osteoporosis. Those previous studies focused primarily on body mass index (BMI), which incorporates measures of muscle and bone mass and subcutaneous fat as well as visceral fat. Dr. Bredella’s work zeroed in on visceral fat.
In the present study, 79 women (mean age, 36 years; mean BMI, 35 kg/m2) with low growth hormone levels were randomized to receive low-dose growth hormone replacement therapy or placebo for 6 months. Subjects received MR spectroscopy to measure bone marrow fat and computed tomography to measure subcutaneous and visceral abdominal fat and thigh muscle mass at baseline and 6 months. Subjects were instructed not to change exercise regimens during the study and were monitored for changes in blood glucose.
One of the most surprising and important findings, according to Dr. Bredella, was that 32% of these obese but otherwise healthy young women were already osteopenic (T-score between –2.5 and –1) at baseline and that one had developed osteoporosis (T-score below –2.5). "It’s important that people become aware that obesity doesn’t protect against bone loss," she said.
Growth hormone was associated with increased P1NP (procollagen type 1 amino-terminal propeptide, a marker of bone formation) and CTX (carboxy-terminal collagen crosslinks, a marker of bone resorption), as well as increased vitamin D, thigh muscle mass, and decreased visceral and subcutaneous abdominal fat, compared with placebo, Dr. Bredella said.
Patients with the greatest abdominal fat loss had the greatest increases in bone formation. Patients with the greatest increases in vitamin D also had the greatest increases in bone formation.
No significant differences were found between the two groups in the more common side effects of growth hormone therapy, including edema of the hands and carpal tunnel syndrome.
"Overall, our patients didn’t lose weight, but they had a redistribution of their body fat and muscle mass," Dr. Bredella noted. "They lost belly fat but increased their muscle mass, and because muscle is heavier than fat, their overall weight didn’t change."
Although the high cost of growth hormone replacement therapy would likely prohibit its widespread use as a treatment for obesity-related bone loss, the results of this study suggest new treatment possibilities. "It’s not going to be the magic therapy for obesity and bone loss, but it could help maybe someone who was unable to lose weight to lower their risk profile for diabetes and cardiovascular disease, and it could be used in the aging population because we know as we get older our growth hormone levels go down," she said.
Dr. Bredella had no disclosures related to this study.