LOS ANGELES -- Anyone seeking the fountain of youth should think twice before turning to growth hormone, a fast-growing trend in anti-aging fringe medicine. If conclusions from an obscure population living in Ecuador prove true, less growth hormone -- not more -- may prevent cancer and diabetes in old age.
The discovery, published Wednesday in the journal Science Translational Medicine, backs up earlier research showing that yeast, flies and rodents live longer -- in some species, as much as 10 times longer -- when they grow slowly.
"There are a lot of people giving human growth hormone to fight aging," said Dr. Nir Barzilai, a researcher at the Albert Einstein College of Medicine in New York, who was not involved in the research. "The question is, will you live longer and healthier? I think these studies suggest, maybe not."
The discovery hinged on a group of extended relatives living in the Andes in Ecuador, many of whom share a genetic mutation that shuts off receptors to human growth hormone. The hormone helps regulate metabolism throughout the body as well as the way that cells change as they age.
The mutation, called E180, is one of several that cause Laron Syndrome, a disorder that stunts growth after birth by about 50 percent.
The most obvious effects of the disorder are negative, said study co-author Dr. Jaime Guevara-Aguirre of the Institute of Endocrinology, Metabolism and Reproduction in Quito, Ecuador. These include short stature -- people with Laron grow to be about 3 to 4 feet tall -- and high infant mortality.
But Guevara-Aguirre, who treats the Laron patients, saw a positive side, too: Virtually none of them got cancer or diabetes.
He eventually joined forces with study co-author Valter Longo, a University of Southern California cell biologist who researches aging. Longo's team had been looking at yeast and mice that also lacked growth genes. Both organisms were about half the normal size; the yeast lived three times longer than normal and the mice lived 40 percent longer.
Longo's team had found that cells from the mutant yeast and mice were protected against DNA damage. The Laron patients provided an opportunity to see if the same held true in humans.
The researchers collected health histories of 99 patients over age 10 as well as death statistics of 53 other Ecuadorans with Laron who died before Guevara-Aguirre began his work in the 1980s. They also collected data on more than 1,600 unaffected relatives of the Laron patients.
There were 30 deaths in the Laron group: eight from heart disease, one from stroke, and 21 from non-age-related causes, including an unusual number from convulsive disorders, accidents or alcohol-related issues.
Only one person got cancer. She did not die from it. Cancer accounted for about 20 percent of deaths of relatives without Laron.
None of those with Laron had diabetes, even though 21 percent of the Laron patients were obese. Diabetes caused 5 percent of relatives' deaths.
The team took serum taken from patients and unaffected relatives and added them to human cells. They found that the serum from Laron patients protected DNA from breakage that can contribute to cancer. Serum from unaffected relatives did not.
The Laron serum also promoted a kind of suicide among damaged cells. This, Longo said, might protect against cancer by killing off cells that are about to turn rogue.
"The results are about as clear as you can get," said Andrzej Bartke of the Southern Illinois University School of Medicine in Springfield, Ill., who has seen similar results in his work on aging in mice.
Experts said the study casts doubt on the use of human growth hormone injections to combat aging. Though the treatment has been shown to improve muscle mass, doctors have worried that it may raise the risk for diabetes and cancer.
Dr. Thomas Perls, a professor of medicine and geriatrics at Boston University and a critic of the growth hormone industry, said the research provides "yet more dramatic evidence that growth hormone does the opposite of what the hucksters and the anti-aging industry promote." He was not involved with the study.
In 2009, Americans spent $1.35 billion on growth hormone treatments, filling 431,000 prescriptions, according to the health care information and consulting company IMS Health.
Longo said the research might lead to drugs that suppress growth hormone to prevent multiple diseases of aging -- much the way statin drugs are used to lower cholesterol and prevent cardiac disease.
The goal of such prevention wouldn't be to live longer, but to live disease-free for as long as possible, he said.
"These mice and the Laron patients don't seem to have chronic conditions," he added. "They live long lives, and then they drop dead."