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Is it time for new indications for GH?
Growth hormone is advertised as ‘anti-aging,’ although no clinical evidence supports that claim.
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When it was approved for use in August 1996, growth hormone was indicated for adults with pituitary failure including those with pituitary tumors, pituitary surgical damage, hypothalamic disease, trauma or confirmed childhood-onset growth hormone deficiency. Since then, growth hormone has received a lot of public attention and interest for uses such as the enhancement of athletic performance and as an anti-aging agent.
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In an interview with Endocrine Today, Shlomo Melmed, MD, senior vice president and chief academic officer of Cedar Sinai Medical Center spoke about the current status of growth hormone treatment in adults, some controversies involving GH and where the field is headed.
Melmed said that, currently, a hot topic in the field of GH is the acceptance of the requirement of GH replacement in adults with true pituitary deficiency.
“Replacement of GH is clinically beneficial to patients who have pituitary hormone failure,” Melmed said. “Until very recently patients with pituitary deficiency were only replaced with thyroid hormone, adrenal steroids or gonadal hormones.”
At that time, GH was not readily available, he said. Furthermore, the condition was not easily recognized. “Adults with GH deficiency will often be obese, hypertensive and sometimes complain of feeling lethargic. These symptoms are very common and it took time to clearly define the clinical features of GH deficiency,” Melmed said.
GH is required to maintain body composition, heart function, overall well being, energy levels and bone metabolism in adults with GH deficiency. “We never previously utilized GH as a required replacement for GH-deficient adults,” he said.
Off-label use
Treating adults with GH deficiency has been somewhat controversial because it is not always clear who will benefit from the treatment, Melmed said. Additionally, GH has garnered a bad reputation due to the abuse of GH by athletes in competitive sports and the illicit use of GH to counter the effects of aging.
Melmed explained that tests to detect illegal use of GH are extremely difficult to develop.
“When you inject GH it can be picked up in a regular clinical assay as being a naturally occurring GH. It is virtually impossible for standard tests to accurately distinguish bottle-derived GH from pituitary-derived GH,” he said. “GH levels are extremely low, even in people with normal levels. Plus, if you inject GH, it will disappear in your system within minutes. Even if someone is abusing GH and injecting it in the morning if they were tested that afternoon, their levels would be measured as normal. Sophisticated tests are required to detect exogenous GH.”
Melmed said that you could also test for GH abuse by measuring the levels of circulating insulin-like growth factor-I. However, the range of IGF-I levels in the body can be wide and are also age and sex-dependent. “If the normal range is from 100 ng/L to 300 ng/L and your levels are around 200 ng/L, and increase to 280 ng/L after injecting GH, it would still appear to be within the normal range,” he said.
GH has been advertised an “elixir of youth,” Melmed said. “The anti-aging industry is very big and is touting GH as a serum for the reversal of frailty and aging. These people are not endocrinologists,” Melmed said. He cited a recent study published in the Journal of the American Medical Association, which suggested that more than 100,000 illegal prescriptions of GH are prescribed annually in the United States.
Any anti-aging effect?
Melmed said that there is little evidence for effect of GH on the aging process. In fact, whether or not to conduct prospective trials to test an effect of GH on aging is a current controversy within the field, he said. “We don’t really know if GH would work better than a good exercise and diet regime,” he said. “A big question is: If you exercise regularly and diet appropriately, will you be better off, as a geriatric patient, with or without GH? We don’t know the answer to that question.”
The concern lies in what effects GH will have in people who have no GH deficiency. “We don’t know if giving GH unnecessarily, when your body is not naturally deficient, may, for example, trigger an underlying cancer,” Melmed said. “If you have an underlying slow-growing cancer and we stimulate that with GH injections, will we or won’t we enhance the likelihood of that cancer becoming manifest? If you already have cancer, will GH make it grow faster?”
Melmed said that research has shown that in patients with true GH deficiency, GH replacement has not increased the incidence of cancer.
The use of GH as an anti-aging drug could also lead to metabolic complications. “GH is a powerful antagonist of insulin action. Too much GH in the elderly may cause the patient to develop diabetes. Other common side effects include fluid retention and severe muscle aches and pains,” Melmed said. “It is the possible side effects that concern us.”
Moving forward, the effect of GH on the aging process needs to be tested. “We need long-term prospective well-controlled trials to answer the question of whether or not GH improves the frailty of aging and to find out whether or not GH improves the quality of life as we age, or in fact prolongs life,” Melmed said. – by Leah Lawrence
Dr. Melmed is a consultant for Eli Lilly’s HypoCCs Program.