Suppression of growth hormone and insulin-like growth factor (IGF-1) also may decrease cancer risk in those individuals at high risk for disease, and perhaps could be a preventive measure, said William E. Sonntag. Ph.D., the lead investigator, who based his findings on research in rats.
He said IGF-1 is an important blood-borne factor that increases cell growth and prevents cell death and has been proposed to be a factor in the initiation of cancer.
"Elevated IGF-1 levels in pre-menopausal women have been demonstrated to be a risk factor for breast cancer as well as numerous other cancers," said Sonntag, professor of physiology and pharmacology at the School of Medicine, a part of Wake Forest University Baptist Medical Center.
IGF-1 in the blood also may act as a tumor promoter during the early development of cancer, he said.
Although additional research is needed, he said, drugs in the somatostatin class are currently available to suppress growth hormone and IGF-1 in people, so somatostatin analogs could be given as preventative measures to lower plasma IGF-1 before the onset of disease, especially in high-risk people.
In a previous study, rats with high levels of growth hormone (a circulating factor that increases IGF-1 levels) exhibit an increase in spontaneous mammary tumors. Dwarf animals with 50 percent lower IGF-1 levels do not develop tumors in response to a chemical carcinogen. But Sonntag said that if these dwarf rats are given growth hormone to increase IGF-1 in the blood, tumors develop at the same rate as in the normal animals.
Suppression of IGF-1 activity inhibits the proliferation of numerous cell types and cancers. "IGF-1 levels in the blood can be reduced by low-calorie diets, which could be a mechanism for the diet-cancer relationship," said Sonntag, whose work explores the neurobiology of aging.
Previous studies in some animals indicate that a reduction in IGF-1 activity increases lifespan. To date, there are no studies of a specific suppression of IGF-1 on aging or age-related diseases.
In the current study, Sonntag found that a life-long deficiency of IGF-1 decreased cancer risk by approximately 45 percent and decreased cancer deaths by 12-15 percent.
"Besides reducing the incidence of cancer in these rats, we found that a modest suppression of plasma IGF-1 beginning shortly after puberty and continued throughout life reduces the incidence of kidney disease and increases lifespan," Sonntag said.