Human growth hormone is produced by the anterior part of the pituitary gland in the brain. Growth hormone has multiple functions within the body, including increasing height and size, muscle mass, and regulating levels of other bioactive substances in the body.
Excess human growth hormone can cause diabetes mellitus, enlargement of peripheral body parts such as hands and feet, arthralgias (joint pains) and even gout. Chronically high levels of growth hormone can result in a condition known as acromegaly, formerly called gigantism.
The most common cause of high levels of growth hormone in humans is a tumor of the pituitary gland. There are many potential different types of tumors that can develop within the pituitary gland. The pituitary gland produces many hormones, and each hormone is produced by a particular cell that can turn cancerous.
A somatotrophic pituitary adenoma is a pituitary tumor of the somatotroph cells that produce growth hormone. A somatatrophic pituitary adenoma will continue to grow slowly, causing increasing levels of hGH over time. If a pituitary adenoma becomes large enough it may cause headaches by increasing the intracranial pressure, and vision changes by compressing the nearby optic nerve.
Occasionally a pituitary adenoma can become large enough to compress the stalk of the pituitary gland. This may cause low levels of other pituitary hormones such as ACTH, MSH, FSH, TSH and LH. When multiple pituitary hormones are decreased, a myriad of symptoms will develop such as fatigue, sleep difficulties, hair loss, cold intolerance, decreased libido and testicular atrophy.
Another possible cause of high levels of human growth hormone (hGH) is a pituitary adenoma that is capable of secreting both growth hormone and prolactin. Approximately 7 percent of all pituitary adenomas fall into this dual hGH-prolactin secreting category.
In the case of an hGH-prolactin secreting pituitary adenoma, the excess prolactin inhibits GnRH secretion from the hypothalamus. GnRH is gonadotropin releasing hormone that stimulates the production of FSH and LH from the gonads. Low levels of FSH and LH result in dysfunction of the reproductive system but, occasionally, the individual may remain asymptomatic. The secretion of the remaining pituitary hormones would remain unaffected unless the tumor becomes large enough to compress the pituitary stalk.
A third potential cause of high levels of human growth hormone comes from an often overlooked source. Several studies have shown that chronic nicotine use can increase serum hGH levels in men. The nicotine may come from tobacco use or nicotine gums or patches. Chronic nicotine use may also increases levels of the hormones cortisol and prolactin. Serum levels of human growth hormone do not stay elevated once nicotine is discontinued. However, the end effects of elevated hGH may be irreversible.