What is human growth hormone (HGH)?
HGH is a hormone that is produced in the pituitary gland of the brain. Once released, it induces the liver to produce insulin-like growth factor 1 (IGF-1) and this hormone then triggers the growth of bones and body tissues. We know that the production of HGH is influenced by stress, sleep, exercise, food intake, and sugar levels. Growth hormone and IGF-1 levels peak during puberty, then gradually decline after the age of thirty. But even though levels decrease, the normal pituitary never completely stops its production of HGH.

Most of our knowledge of HGH comes from studying individuals who lack these hormones. In children HGH deficiency causes stunted growth and development. In adults, significant deficiency may result from disease, tumors, surgery or radiation that destroys critical areas in the pituitary. This then leads to weight gain, lipid (cholesterol) abnormalities, coronary vascular disease, fatigue, decreased immune response, loss of muscle, and osteoporosis. These individuals are also prone to depression and problems with sexual function. When they are injected with corrective amounts of HGH, many of these problems resolve.

HGH declines with age. Does replacement prevent weight gain, loss of muscle and bone mass, and in general keep us in better shape and health?
The answer is that we're not sure. The types of studies we should be using to resolve this question are few, small and have rarely included women. Here are some of the more notable ones: HGH case studies.