Sci. Aging Knowl. Environ., 27 November 2002
Lean, Yes--But Mean?
Growth hormone thins and strengthens the elderly, but at a cost
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/abstract/sageke;2002/47/nw158
Key Words: IGF-1 lean body mass VO2 max
Abstract: Growth hormone (GH) rewinds the years, countless supplement-peddling Web sites proclaim. But scientific evidence of the molecule's benefits remains scant, and the risks of long-term GH therapy are unknown. According to a new study, GH reduces fat and increases muscle in older people, and it might make them stronger and more fit. Frequent side effects, however, indicate that GH therapy still faces considerable growing pains.
As people age, they produce less GH, a compound that stimulates bone and muscle growth and regulates metabolism. The deficit might spur some age-related health problems, such as reduced muscle mass and increased fat deposition. However, mice with genetic defects that cripple the GH pathway live longer than normal, and a disorder of excess GH, called acromegaly, makes people die young (see Bartke Viewpoint). GH's contribution to life-span and infirmity in the elderly is unclear, but some studies suggest that supplementing GH might be helpful: Elderly men trim down and gain bone density when given GH.
Production of sex steroids--testosterone in men and estrogen in women--also diminishes with age. (The wisdom of hormone replacement remains controversial; see "More Than a Hot Flash" and Web Links: "Sorting Through the Confusion Over Estrogen" and "The Search for Alternatives to Hormone Replacement Therapy"). These hormones collaborate with GH to spur growth during puberty, so Blackman and colleagues wondered whether they could enhance the positive effects of GH in the elderly.
The researchers treated 131 men and women aged 65 to 88 with either GH and sex steroids together, GH alone, sex steroids alone, or placebos. During the 26-week study, the researchers measured body composition, muscle strength, cardiovascular endurance, and overall health. As in previous studies, individuals who received GH gained muscle mass and lost fat. Men who received testosterone in addition to GH improved more than those on GH alone did, whereas women did not derive additional benefit from estrogen. The added muscle mass didn't necessarily bestow extra strength, however: GH did not fortify muscular prowess in women, regardless of whether they received estrogen; men gained marginal strength only if they took both GH and testosterone. Aerobic capacity increased in individuals receiving GH; men showed even greater benefit when they also took testosterone. The improvements came with costs, however: A significant percentage of GH-treated subjects suffered from joint pain or carpal tunnel syndrome, and half of the GH-treated men developed glucose intolerance or diabetes, compared with only 3 out of 17 controls.
This is the first study to test the combination of GH and sex steroids, says endocrinologist Anne Cappola of the University of Maryland School of Medicine in Baltimore: "The results suggest that, at least in men, it may be useful to have both." GH imparts significant changes, says Cappola, although it's still unclear whether those changes would markedly improve elderly people's health. The results warrant further study, but the high probability of side effects means that GH "is definitely not for public use yet," she says. GH might hold promise for the future, but for now the claims that sound too good to be true are just that.
--R. John Davenport; suggested by Arlan Richardson
Citation: R. J. Davenport, Lean, Yes--But Mean? Science's SAGE KE (27 November 2002), http://sageke.sciencemag.org/cgi/content/abstract/sageke;2002/47/nw158
Science of Aging Knowledge Environment. ISSN 1539-6150