IGF-1, or insulin-like growth factor-1, is a hormone produced by the liver in response to growth hormone stimulation. It plays a key role in regulating cell growth, differentiation, and proliferation. IGF-1 is important for both fetal and postnatal growth and development, and it also helps to maintain the function of a variety of tissues and organs throughout the lifespan. Abnormal levels of IGF-1 have been associated with a variety of diseases, including cancer, diabetes, and cardiovascular disease. IGF-1 is sometimes used as a marker for growth hormone deficiency or excess, and it is also sometimes used as a supplement to enhance athletic performance.