They found that animals with a deficiency in growth hormone initiated after adolescence had up to a 14.6 percent increase in lifespan. All animals in the study lived until they died of natural causes.
The researchers used several tests to measure memory and learning. They found that growth-hormone-deficient rats had impaired learning ability compared to normal animals of the same age. A similar pattern occurred in memory tests.
"The presence of growth hormone and IGF-1 are required for optimal performance on tests of learning and memory throughout life," they said. "Growth hormone/IGF-1 replacement in older animals reverses the age-related decline in cognitive function."
The group also found that "cartilage degeneration that normally accompanies aging is accelerated by the absence of growth hormone."
The researchers concluded that cancer risk as well as other age-related pathologies could be substantially decreased in these animals by inducing a modest deficiency of growth hormone and IGF-1 early in life. However, there is a tradeoff and deficiency of growth hormone and IGF-1 may impair learning and memory and accelerate some degenerative diseases.