Many of the body's functions are regulated by hormones. Hormones are released into the blood stream from glands or organs. Hormones bind to the surface of cells and exert an effect on the cell's function. Most hormones decline with advancing age. In particular, levels of growth hormone and insulin-like growth factor (IGF-1) in the blood decline substantially with age. IGF-1 is released by the pituitary gland into the bloodstream. The hormone binds to cells all over the body, including the brain, exerting a growth effect. A decline in this hormone is thought to result in a reduction of activity of cells.

William Sonntag and his colleagues at Wake Forest University School of Medicine are investigating the role of growth hormone and IGF-1 in aging, and their possible use as biomarkers of aging.

They've shown that the levels of these hormones decrease with age and, in an animal model, when IGF-1 is injected back into animals that are deficient in the hormone, age-related changes are reversed. This suggests that a diminishment of these hormones contributes to the aging process.

The age-related effects of growth hormone and IGF-1 on bone and muscle mass have been studied extensively. Dr. Sonntag is looking at the effects of reduced IGF-1 in the brain. One brain region that suffers the most from aging is the hippocampus. This area, which plays a major role in memory and other cognitive functions, tends to shrink with age, and fewer new brain cells are formed.

In a study by Dr. Sonntag and colleagues on rats, they found that IGF-1 appeared to regulate the formation of new brain cells in the hippocampus. Theoretically, therefore, a decline in IGF-1 with age could be partly responsible for memory difficulties and other cognitive difficulties some people experience in older age.

If these findings are shown to be true for humans as well as rodents, levels of growth hormone and IGF-1 could be a biomarker of aging.