Insulin-like Growth Factor 1 (IGF-1) is often confused with steroids, especially given its association with muscle growth and athletic performance. This article clarifies what IGF-1 is and differentiates it from anabolic steroids by explaining their fundamental differences in structure, function, and regulation.
Understanding Insulin-like Growth Factor 1
Insulin-like Growth Factor 1 (IGF-1), also known as somatomedin C, is a polypeptide hormone. It consists of a single chain of 70 amino acids, folded into a specific three-dimensional shape by three intramolecular disulfide bridges.
The liver is the primary site for IGF-1 production, although other tissues like muscle also produce it in smaller amounts. Its synthesis and secretion are largely stimulated by growth hormone (GH). IGF-1 functions as a mediator of many of growth hormone’s effects, acting as a growth factor throughout the body.
Key Differences Between IGF-1 and Steroids
IGF-1 and anabolic steroids differ fundamentally in their chemical composition and how they interact with cells. IGF-1 is a peptide hormone. In contrast, anabolic steroids are lipid-based molecules characterized by a specific four-ring carbon skeleton, similar to cholesterol.
These structural disparities lead to entirely different mechanisms of action within the body. IGF-1 exerts its effects by binding to specific IGF-1 receptors (IGF-1R) on the surface of target cells. This binding initiates a cascade of intracellular signaling pathways, promoting protein synthesis and cell proliferation. Anabolic steroids, conversely, typically pass through the cell membrane to bind with androgen receptors inside the cell, directly influencing gene expression. While both can promote muscle growth, they achieve this through distinct biological pathways.
How IGF-1 Functions in the Body
IGF-1 performs diverse physiological roles across various tissues, mediating many anabolic effects of growth hormone. It contributes to cell growth, proliferation, and differentiation. This includes its involvement in skeletal muscle hypertrophy, where it stimulates protein synthesis and helps prevent muscle atrophy.
The hormone also plays a part in metabolic processes, influencing glucose and lipid metabolism. IGF-1 promotes the uptake of glucose into cells and supports glycogen synthesis. It further contributes to the health of connective tissues, promoting collagen synthesis in tendons, and is involved in bone development. Beyond these roles, IGF-1 is also recognized for its neurotrophic effects, aiding in the survival of nerve cells and supporting neural development.
IGF-1 Regulation and Misuse
The body’s IGF-1 levels are tightly regulated by several factors, with growth hormone (GH) being the primary driver of its production. Nutritional status also influences IGF-1 concentrations; adequate protein intake is needed for normal synthesis, while caloric restriction or malnutrition can lead to decreased levels. Factors such as age, sex, exercise, and stress can also cause variations in circulating IGF-1.
Due to its anabolic properties, including promoting muscle growth, tissue regeneration, and improved recovery, IGF-1 has been subject to misuse, particularly in sports and bodybuilding. The World Anti-Doping Agency (WADA) classifies IGF-1 as a prohibited substance under the S2 category of peptide hormones and growth factors, banning its use in and out of competition. Misuse of exogenous IGF-1 can lead to various adverse effects, such as hypoglycemia (low blood sugar) due to its insulin-like actions, insulin resistance with prolonged use, and long-term conditions like acromegaly, which involves abnormal tissue enlargement, along with impacts on the heart, joints, and liver.