SAN DIEGO — Stimulating the production of growth hormone in healthy older men and women can return hormone levels to those found in younger adults and reduce body fat, according to research being conducted at the University of Washington and the Veterans Affairs Puget Sound Health Care System in Seattle. Preliminary results of the study are presented June 12 in San Diego at the annual meeting of the Endocrine Society.
Principal investigator Dr. Michael Vitiello of the UW Department of Psychiatry and Behavioral Sciences, along with Drs. George Merriam and Robert Schwartz of the UW Department of Medicine and the VA, are studying the use of GH-releasing hormone (GHRH), a growth hormone stimulator, to increase production of growth hormone in 60 healthy men and women over age 65. GHRH is normally produced in the brain by the hypothalamus and stimulates production of growth hormone by the pituitary.
Although growth hormone is known best for promoting growth in childhood, it has important actions in adults. It regulates body fat, increases muscle mass and capacity for aerobic exercise, and may support normal mood and cognition. Some effects are carried out by stimulating increased production of insulin-like growth factor-I (IGF-I) in the liver and other tissues.
Secretion of growth hormone decreases with age, and many changes of aging resemble abnormalities seen in younger people with growth hormone deficiency: reduced strength and energy, increased body fat (especially around the abdomen) and psychological changes. Some studies suggest that age-associated changes in sleep and cognition may also be related to this decline in growth hormone.
Loss of muscle mass and strength are major problems for the elderly, leading to more falls and increased difficulty coping with tasks of independent daily living. Hormones or other agents that promote muscle strength and energy could help seniors remain independent longer.
In this blinded study, participants gave themselves injections of synthetic GHRH or a placebo (inactive substance) each evening for five months. Before and after treatment, subjects were tested at the UW Clinical Research Center for hormone levels, body composition, physical performance and psychological function. Overnight measurements assessed sleep quality and changes in growth hormone levels.
Compared to placebo, GHRH boosted the nighttime secretion of growth hormone by approximately 35 percent, which in turn led to an increase of 50 percent in blood IGF-I levels in men, and 20 percent in women. There was a moderate but significant reduction in body fat (about 5 percent) in both men and women. The hormone effects occurred in both men and women, but there were suggestions that estrogen replacement in women may partially block some of GH’s effects. Effects on sleep and physical capacity are still being evaluated in this ongoing study.
The investigators noted that the effect of the injections seemed to last only two to three hours. They speculated that a longer-acting GHRH preparation might have even stronger effects.
Side effects of the GHRH injections were generally mild, although a few patients noted fluid retention or local reactions at the injection site.
The investigators caution that these early results do not mean that growth hormone or GHRH should now be recommended as routine treatment or as preventive medicine. Much more work, including completion of this study and a companion UW/National Institute on Aging study being led by Schwartz that examines the combination of GHRH and exercise, is needed to determine the benefits, risks and most appropriate context for boosting growth hormone in older adults.
The study is supported by the National Institute of Mental Health and Veterans Affairs. The GHRH is provided by Serono Laboratories.