Nearly 400 adults from 65 to 84 years old were enrolled in the study, and were divided into groups receiving a placebo or one of four different levels of an oral growth hormone secretagogue (GHS), which stimulates the secretion of human growth hormone. Researchers measured the participants' fat and lean body (muscle) mass, as well as their performance in physical tests like stair climbing and a heel-to-toe walk. The participants also received blood tests for levels of growth hormone and a compound called IGF-1, a hormone which responds to growth hormone and mediates some of its effects.
Participants receiving the GHS treatment saw a significant increase in lean body mass – about 1.5 kilograms, or 3.3 pounds. The GHS treatment led to improved physical function over the six- to 12-month study period. Participants also had higher levels of growth hormone and IGF-1 in their bloodstreams. Patients receiving the GHS treatment had minor side effects, including increased fatigue, insomnia, and fasting glucose levels.
Growth hormone is vital in childhood growth, and production of the hormone peaks during puberty. However, it continues to affect physical function throughout our lives, and it regulates metabolism and body composition. As adults move into middle age, growth hormone production begins to taper off. Many of the effects of aging – increased abdominal fat, reduced muscle mass, and decreased physical function – look very similar to the symptoms of growth hormone deficiency in younger people. As those aging effects set in, many older adults find it difficult to care for themselves, and they lose quality of life and often turn to long-term care.
"If we had something that could reduce that drop-off in physical function, we could improve the quality of life for older adults, and help cut the cost burden of long-term care," explained Merriam. "What we'd like to do is take the steep curve of physical function decreasing with age, and make that a much shallower decline or even a plateau, so people will retain more physical mobility and strength as they age instead of deteriorating."
Researchers studying the aging process believe that growth hormone and IGF-1 may be two of the key compounds that regulate the effects of aging, and that stimulating production of the hormones could help stave off those effects. Other studies have shown that treatments can increase the levels of growth hormone and IGF-1, and can help improve a patient's body composition. However, this study is the first to show not just a stabilization of physical function, but an improvement.
"This is a proof of concept that GHS can help with body composition and physical function," Merriam said. "These are very encouraging results, and we should examine further whether GHS can help in the long term to mitigate some of the negative effects of aging." He added, however, that many steps remain to determine whether this concept could be turned into an effective and safe treatment. The GHS used in the study was discovered and developed by Pfizer Global Research and Development, and is only available for research purposes, not as a prescription or over-the-counter drug.
In addition to the University of Washington and Duke University sites, this study included researchers at Stanford University, the University of Arkansas, Johns Hopkins University, and the Veterans Affairs health care system. The research was supported by Pfizer, Inc.
Note: This research will be featured in a press briefing on Wednesday, June 21, at the International Congress of Neuroendocrinology. Reporters may also participate in the briefing via conference call. For more information about the ICN meeting or press briefing, visit: http://newsbureau.upmc.com/ICN2006/
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