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Is Growth Hormone a Fitness Pill for Elderly?

Capromorelin - an investigational drug that stimulates cells to secrete growth hormone - may offer a source of physical improvement among elderly people, according to new research.

In a recent trial, capromorelin improved physical function by 10% in men and women aged 65 or older, after 12 months of treatment, said George Merriam, MD, of the University of Washington in Seattle, and colleagues.

According to Dr Merriam and colleagues, study participants who took capromorelin for six months showed a significant improvement in tandem-walking (walking one foot in front of the other), and after 12 months, they had significantly improved in stair-walking (a standard test of physical function and one of several measures used to evaluate the ability to live independently.

"These improvements were small, but real, not just statistical flukes," Dr Merriam reportedly said. She added that participants on active treatment also reported feeling "more vim and vigor when taking the drug. They regretted stopping the drug at the end of the study."

However, despite the promising results, Dr Merriam notes that they are "preliminary and really more a proof of concept that could perhaps-with a larger study over a longer period-translate into a meaningful clinical benefit."

This "clinical benefit" would translate not into longer survival, but into a more extended period of fitness during aging, permitting people to live independently for longer.

Clinical Trial

The study by Dr Merriam and colleagues included 395 men and women (aged 65-84 years), who were living independently but with mild functional impairment, such as reduced walking-speed or reduced grip-strength.

Participants were randomized to receive capromorelin in four dosing-groups, or placebo, for up to 12 months.

Among a predetermined portion of participants in both the treatment and the placebo groups, researchers serially measured growth hormone and insulin-like growth factor I (IGF-I) from 8 PM- 8 AM at baseline and at two months.

All active doses of capromorelin "prompted acute growth hormone peak and an increase in overnight growth hormone secretion." The highest peak occurred in participants receiving 10mg three times weekly and the lowest in participants who received 10mg twice daily.

A direct relationship was observed between dose and IGF-I levels, with the highest IGF-I level observed among participants taking 10mg twice daily and the lowest level observed in the placebo group.

"All doses of growth hormone secretagogue were associated with an increase in lean body mass," Dr Merriam reportedly said. One average, the increase was 1.4 kg (approximately 3.3 pounds).

Growth Hormone Secretagogues

Growth hormone production slows to almost nil in elderly people. The lack of growth hormone is believed to contribute to lean muscle-mass loss, which in turn reduces muscle function, according to Dr Merriman.

Studies using growth hormone injections to slow or reverse the aging process have shown that, while such injections may increase growth hormone levels and improve lean muscle mass, their ability to improve function was unclear.

Dr Merriman and other researchers believe that administration of growth hormone "secretagogues" - i.e., supplements of naturally occurring substances in the body that cause growth hormone secretion - offers a more natural approach to raising growth hormone levels, as the secretagogues increase production of growth hormone in "brief pulses which better mimic the body's own production of growth hormone."

Two groups of secretagogues are available: growth hormone releasing hormone GnRH, which requires injection; and ghrelin-mimetics, usually orally administered compounds that are similar to ghrelin, a hormone that also stimulates production of IGF-I.

The study by Dr Merriam and colleagues was supported by Pfizer, which is developing capromorelin. Dr Merriam reported that Merck has a similar compound in development.

Dr Merriam added that, because aging is not considered a "disease or medical condition that requires treatment," the US Food and Drug Administration is setting very high standards to approval of any so-called anti-aging drugs. Although encouraging, he said that the data from this study would not meet such standards.

Posted: June 2006