IGF-1 (insulin-like growth factor 1) is a hormone structurally similar to insulin, produced primarily by the liver in response to growth hormone (GH) stimulation. Unlike GH, which is released in brief pulses and has a short half-life, IGF-1 circulates at stable levels throughout the day — making it a much more reliable marker of growth hormone status than a single GH measurement.

IGF-1 promotes cell growth, proliferation, and survival across multiple tissue types including muscle, bone, and the brain. Low IGF-1 may indicate growth hormone deficiency, malnutrition, or liver disease. Elevated IGF-1 is the primary marker used to diagnose acromegaly (excess GH from a pituitary tumour) and is used to monitor treatment response. IGF-1 also declines with age and has been studied as a marker of biological ageing and longevity.