Somatotropin; GH; human growth hormone; HGH
Growth hormone is released into the bloodstream from the anterior pituitary gland. The pituitary gland also produces other hormones that have different functions from growth hormone.
Growth hormone acts on many parts of the body to promote growth in children. In adults, it does not cause growth but it helps to maintain normal body structure and metabolism, including helping to keep blood glucose levels within set levels.
Growth hormone release is not continuous; it is released in a number of ‘bursts’ or pulses every three to five hours. Growth hormone release is caused by another hormone (growth hormone-releasing hormone), which is released from a point higher up in the brain (the hypothalamus) and it causes the pituitary gland to release the growth hormone.
Growth hormone levels are increased by sleep, stress, exercise and low glucose levels in the blood. They also increase around the time of puberty. Growth hormone release is lowered in pregnancy and if the brain senses high levels of growth hormone or insulin-like growth factors already in the blood. This reduction in growth hormone levels is affected by another hormone called somatostatin.
Not surprisingly, too much growth hormone causes too much growth.
In adults, excessive growth hormone for a long period of time produces a condition known as acromegaly, in which patients have swelling of the hands and feet and altered facial features. These patients also have organ enlargement and serious functional disorders such as high blood pressure, diabetes and heart disease. Over 99% of cases are due to benign tumours of the pituitary gland, which produce growth hormone. This condition is more common after middle-age when growth is complete so affected individuals do not get any taller.
Very rarely, increased growth hormone levels can occur in children before they reach their final height, which can lead to excessive growth of long bones, resulting in the child being abnormally tall. This is commonly known as gigantism (a very large increase in height).
Overproduction of growth hormone is diagnosed by giving a sugary drink and measuring the growth hormone level over the next few hours. The sugar should cause growth hormone production to reduce. However, this does not happen in acromegaly.
Too little growth hormone (deficiency) results in poor growth in children. In adults, it causes a reduced sense of wellbeing, increased fat, increased risk of heart disease and weak heart, muscles and bones. The condition may be present from birth where the cause can be unknown, genetic or due to injury to the pituitary gland (during development or at birth).
Growth hormone deficiency may also develop in adults due to brain injury, a pituitary tumour or damage to the pituitary gland (for example, after brain surgery or radiotherapy for cancer treatment). The main treatment is to replace the growth hormone using injections - either once a day or several times a week.
In the past, growth hormone treatment was stopped at the end of growth. It is now clear that growth hormone contributes to both bone mass and muscle mass reaching the best possible level, as well as reducing fat mass during development to an adult. The specialist is therefore likely to discuss the benefits of continuing growth hormone after growth has completed until age 25 to make sure bone and muscle mass reach the best possible level. Additionally, growth hormone has been linked to a sensation of wellbeing, specifically energy levels. There is evidence that 30-50% of adults with growth hormone deficiency feel tired to a level that impairs their wellbeing. These adults may benefit from lifelong treatment with growth hormone. Taking growth hormone when adult will not result in increased height.
Last reviewed: Dec 2014