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Human Growth Hormone Reverses Effects of Aging
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Treatment with human growth hormone can significantly reverse many effects of aging on the body, a new study has found.
In a clinical trial of 21 healthy men ranging in age from 61 to 81, researchers found that after six months of injections of a genetically engineered version of the natural body hormone, the men emerged with bodies that by many measures were almost 20 years younger than the ones they started with.
But researchers cautioned that the results were highly preliminary and that the long-term side effects of growth hormone remain unknown.
''This is not a fountain of youth,'' said Dr. Daniel Rudman of the Medical College of Wisconsin in Milwaukee, the leading author of the paper, which appears today in The New England Journal of Medicine. ''We need to emphasize that the aging process is very complicated and has many aspects.''
The benefits of human growth hormone observed in his new study, he said, address only one aspect of how the body ages.
Nevertheless, endocrinologists and gerontologists hailed the new study as very promising.
''In my view this is an extremely exciting and positive finding,'' said Dr. John D. Baxter, director of the metabolic research unit at the University of California at San Francisco and a member of the first group to isolate and produce the recombinant version of human growth hormone. ''It's a suggestion that growth hormone can be used much more extensively in old people to promote muscle mass and help get rid of obesity. The net effect of a guarded use of the hormone might be very healthy.''
In the trial, hormonal treatment had its biggest effect on body composition. Although the weight of the men remained the same, they shed nearly 15 percent of body fat and gained almost 9 percent in lean body mass. Diet and exercise were kept constant for those tested. Part of that added bulk occurred in the muscles, while the rest is thought to have helped rebuild vital organs like the heart, kidneys and the gastrointestinal tract, which often shrink with age.
The men's skin regained a youthful thickness, and the level of an important growth-stimulating hormone in the blood returned to that of those under the age of 40. The bones of the spine also gained in mass, although other parts of the skeleton did not.
'Their Physique Changed'
''Their physique changed,'' Dr. Rudman said. ''They had the appearance of being more fit and in better condition.''
The results strongly suggest that a decline in human growth hormone production is one critical factor that causes fat to gather, muscles to wither and organs to atrophy as the body ages.
Dr. Rudman said that while his study involved only men, growth hormone applications were likely to have the same impact on women. But he warned that he and his colleagues still did not know whether the changes in body composition and organ size induced by growth hormone treatment translated into improvements in organ function or even better overall health.
Dr. Rudman and other experts also cautioned that the men in the study were inoculated for only six months, and that long-term or wanton administration of the hormone could have severe side effects.
''Too much growth hormone can cause arthritis, diabetes, enlargement of the face and hands, even heart failure,'' said Dr. Mary Lee Vance, an endocrinologist at the University of Virginia in Charlottesville, who wrote an editorial that accompanies the report. ''This hormone is a double-edged sword.''
Hopes for Helping Elderly
Researchers say that judicious administration of human growth hormone could prove of vast benefit for those elderly people whose muscles are wasting away or who need greater strength to help them recover from a hip fracture, stroke or other debilitating illness.
''The decline in muscle function is a significant thing in aging,'' said Dr. Michael L. Freedman, director of geriatrics at New York University Medical Center. ''Giving the hormone to elderly people may prevent a lot of complications.''
And researchers said that while initial therapeutic use of the growth hormone would probably be confined to frail elderly people, it could eventually be employed more widely to help prevent body changes in the 25 million elderly Americans whose bodies have stopped producing useful amounts of human growth hormone.
Studies of the effects of human growth hormone on the body are relatively new because researchers have only recently had adequate supplies of the substance to perform experiments. Normally the hormone is secreted in very tiny amounts by the pea-sized pituitary gland at the base of the brain.
How Growth Hormone Works
The hormone circulates through the body and stimulates the production of another compound called insulin-like growth factor-1, a powerful protein that spurs tissue growth and helps maintain organ health. In most people, the production of human growth hormone by the brain begins declining at age 30, and after the age of 60 is only a fifth or so of its youthful high.
Children born with a deficiency of human growth hormone never grow much taller than three or four feet unless given hormone injections. Until recently the minute amounts of the hormone that were isolated from the pituitaries of human cadavers were reserved to treat that form of hereditary dwarfism.
But within the last few years genetic engineers have perfected a method for mass-producing a recombinant form of the hormone, allowing researchers to begin experimenting with the hormone for disorders beyond childhood dwarfism.
In two other recent studies, doctors examined the effects of growth hormone on young adults who had diseases that entirely suppressed hormonal secretion by the pituitary. The results of those studies hinted that growth hormone can influence the relative composition of fat and muscle in the body.
The new study is the first investigation of the effects of growth hormone treatment on healthy older people who had small but still measurable levels of the growth hormone. And the findings ''are the most dramatic we've seen so far,'' Dr. Freedman said.
Twelve of the men chosen for the study were given injections of the synthetic hormone three times a week, at a dose calibrated to equal the hormone output of a young man. Nine men in the study who served as controls received no treatment. All were assigned a similar diet of protein, carbohydrates and fats.
After six months, all the men receiving the hormone had dropped body fat while gaining muscle mass and skin thickness. They also exhibited blood levels of insulin-like growth factor-1 equal to that of far younger men. Through X-ray analysis the researchers determined that the muscles and organs had grown, although they have not yet learned exactly how much any organ may have increased.
Dr. Rudman said the changes were extremely significant. He pointed out that after the age of 40 or so, most people start losing lean muscle mass at a rate of about 5 percent a decade, and gaining body fat at more or less the same rate.
When compared with the 9 percent gain in lean body mass seen in the new study, he said, the results mean that six months of hormone treatment essentially cut almost two decades of age-induced changes off the subjects' bodies. Although the researchers are not yet certain how long the beneficial effects of hormone injections last, they suspect that once treatment is discontinued, the body composition will gradually revert to its former state.
Many Unanswered Questions
The scientists must further determine whether the bigger organs and muscles work any better or more youthfully than they did before.
''They don't know if organ function has improved, if the body is better able to metabolize food and handle nutrients, if the overall well-being of the person has benefited,'' Dr. Vance said. ''This is an important first study, but many questions remain to be answered.''
Dr. Rudman agreed that the findings were preliminary. He said that although the participants in the study suffered only mild side effects from the treatment, including a slight rise in blood pressure, the long-term consequences of growth hormone treatment are still in question.
''We have no idea what will happen if we start treating a lot of people with this stuff,'' Dr. Freedman said. ''Even it if makes you have more muscle or makes your skin better, if it ends up increasing something in the kidneys or gastrointestinal tract that leads to cancer, that's no good.''
A version of this article appears in print on , Section A, Page 1 of the National edition with the headline: Human Growth Hormone Reverses Effects of Aging. Order Reprints | Today’s Paper | Subscribe