Growth hormone (also known as somatotropin) is a peptide hormone produced in the pituitary gland and released into the blood for circulation around the body. Growth hormone is necessary for the reproduction of cells and stimulation of growth processes in the body. When levels of growth hormone are low, a person may experience thinning hair and hair loss
Secretion of growth hormone is regulated by the hypothalamus which is in turn dependent on nutrition, dehydroepiandrosterone (DHEA), vigorous exercise, sleeping patterns, niacin (vitamin B3) and hormones such as androgen and estrogen. Growth hormone is inhibited by free fatty acids, stress, dihydrotesterone (DHT), high blood sugar and cortisol.
Growth hormone also supports the action of vitamin D in that it aids calcium retention, increases the synthesis of proteins, maintains normal function of the immune systems and supports the conversion of thyroid hormone for increased metabolism.
Growth hormones can not penetrate cells so they rely on binding to receptors to activate certain pathways. One pathway that growth hormone stimulates is the JAK-STAT signalling pathway. Disturbances in JAK signalling is linked to hair loss conditions such as alopecia areata. Growth hormone stimulates insulin-like growth factor (IGF-1) stimulation in the liver. IGF-1 is essential for the continuation of a normal hair growth cycle and the prevention of thinning hair.