There are two primary types of insulin-like growth hormone: the insulin-like growth factor 1 (IGF-1) and the insulin-like growth factor 2 (IGF-2). Both of these insulin-like growth hormones are naturally produced by different types of cells and have the same molecular structure as the hormone insulin, hence their names. They also have similar functions to insulin, and are vital elements in a person’s growth and memory. IGF-1 and IGF-2 are also known as somatomedin C and somatomedin A, respectively.
The discovery of the insulin-like growth hormone came about after the discovery and isolation of insulin in 1916. In the 1950s, many studies led scientists to suspect that growth hormones were not directly responsible for some bone growth activities in the fetus, but instead acted through some kind of catalysts that scientists dubbed as “serum factors.” Some laboratory experiments involved culturing insulin with an antibody-filled serum that was supposed to remove all insulin functions, but some functions still remained and were attributed to “insulin-like” elements. After more than two decades, scientists succeeded in isolating and characterizing the insulin-like growth hormone, or insulin-like growth factors (IGF).
Between the two IGFs, the IGF-2 plays a more prominent role during gestation, or the period when the fetus is still developing in the womb. Its presence signals the cells to multiply and divide into different types so more solid tissues can form. The insulin-like growth hormone also encourages the secretion of progesterone, an important hormone for fetal development and for menstruation. Studies in the late 2000s found that IGF-2 may be an important factor in treating Alzheimer’s disease and other memory disorders such as post-traumatic stress disorder. The IGF-2 gene, or the gene that helps produce the IGF-2, is inherited both from the male and female parent, but only the copy from the male parent becomes active in the fetus’ body.
In contrast to the IGF-2, the IGF-1 is more active in an adult body and its presence affects the growth of the musculoskeletal system, nervous system, and vital organs such as the kidney, liver, and lungs. In fact, almost every type of cell within the body needs the IGF-1 to develop. The amount of IGF-1 produced in the body is usually highest during the adolescent period, and then gradually decreases. Many studies have shown that children who are shorter than normal may have deficient amounts of the insulin-like growth hormone, and experimental IGF-1 therapies somehow increased their height. Interestingly, some studies have found that reduced levels of IGF-1 in adults may delay signs of aging, induce proper weight loss, and promote longevity.