What is Growth Hormone and How Does It Affect Us as We Age?
About Growth Hormone
The pituitary gland is located in the brain directly below the hypothalamus, and is about the size of a small marble. The most abundant of the pituitary hormones is growth hormone (GH) or somatotrophin. As the name implies, GH is important in controlling our body’s growth and development. GH stimulates bone growth, promotes internal organ growth, assists with the development of tissues such as fat (adipose) and muscle. GH also controls the development of the reproductive organs. GH is usually secreted during the early hours of sleep and also in response to stress.
GH levels in the body are at their highest during our early years and puberty, declining once we reach our adult body size and physical and reproductive maturity. This means that GH levels in the elderly are considerably lower than GH levels in young adults.
As we age, the hypothalamus in the brain secretes less GH-releasing hormone (GHRH), which causes a decrease in the amount of GH produced and released by the pituitary gland. This decline in GH levels then causes a reduction of IGF-1, or insulin-like growth factor 1, which mediates GH action. These declining levels are often referred to as the ‘somatopause’.
Growth hormone was first identified in the fifties, although it was only in the sixties that it began to be used as a treatment. Since then, other clinical trials established the capacity of GH as treatment for some health conditions, including a specific syndrome related to growth hormone deficiency in adults, known as adult growth hormone deficiency, or AGHD.
Growth Hormone In Adult Life
After about the age of 30, growth hormone secretion declines, although it still plays an important role in our metabolism. GH helps break down fat for energy, regulate protein into muscle mass and conserve sugars in the body. It also plays a role in cholesterol storage, healthy bone density and heart function.
The reduction in GH levels means that our body composition changes. There is an increase in fat mass and a decrease in lean mass and bone density, leading to an increased risk of obesity, frailty and bone fractures. There are also wasting processes taking place in other parts of the body, such as the kidneys and the spleen. Our skin quality alters, with thinning, dryness and wrinkles appearing. At the same time though, the changes in our hormones and endocrine system may protect us from cancer and age-related conditions.
It is suggested by some that the amount of GH secreted in earlier years may limit our life expectancy. Some studies show that calorie restriction in humans and other species can cause a slower and longer GH release, increasing life expectancy. Unfortunately, individuals that suffer with medical GH deficiencies show that the consequences of suppressing GH can cause other severe health problems.
Although there is extensive debate around whether GH can prevent, or even reverse aging, some studies do show an influence in aging. A number of researchers report improvements in body composition and some animal studies have also shown that an increase in growth hormone can increase lifespan. However, other studies report negative impacts, including one study that demonstrates a higher mortality rate in patients who received GH as part of their treatment regime.
Currently human growth hormone (hGH) is available for a number of conditions, including Prader-Willi syndrome and Turner syndrome and it has yet to be approved as an anti-aging therapy.
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Last reviewed 26/Feb/2014