Insulin-like Growth Factor 1 (IGF-1) is a potent anabolic hormone that plays a central role in human growth and development. It acts as the primary mediator for many of the effects of Growth Hormone (GH), linking the signals from the pituitary gland to growth in target tissues throughout the body. The molecule is instrumental in promoting cell proliferation and survival in nearly every cell type. For those seeking to increase muscle mass, the answer to whether IGF-1 builds muscle is unequivocally yes, as it is a core driver of muscle hypertrophy.
What is Insulin-like Growth Factor 1?
Insulin-like Growth Factor 1 is a small protein hormone with a molecular structure similar to insulin, which is why it carries the “insulin-like” designation. The hormone is a key component of the somatotropic axis, also known as the GH-IGF-1 axis, which governs overall body growth. IGF-1 is produced throughout life, with the highest levels occurring during the pubertal growth spurt and declining with age.
The liver is the principal source of circulating IGF-1, secreting it into the bloodstream in response to stimulation by Growth Hormone released from the pituitary gland. Once in the circulation, this IGF-1 acts as an endocrine hormone, traveling to distant target tissues like skeletal muscle to promote systemic growth.
IGF-1 is also produced locally by many other tissues, including muscle itself, where it acts in a paracrine or autocrine fashion. This locally produced IGF-1 is particularly important for immediate tissue repair and regeneration, especially following mechanical stress like exercise. Most circulating IGF-1 is bound to one of six Insulin-like Growth Factor Binding Proteins (IGFBPs), which controls its half-life and bioavailability.
How IGF-1 Signals Muscle Development
The mechanism by which IGF-1 promotes muscle growth starts with its binding to the Insulin-like Growth Factor 1 Receptor (IGF-1R) on the surface of muscle cells. The IGF-1R is a tyrosine kinase receptor, and its activation initiates a complex set of intracellular signaling cascades. This interaction translates the hormonal signal into physical muscle change.
The most significant pathway activated is the Phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Akt, also known as Protein Kinase B, regulates both protein synthesis and protein degradation. Activation of Akt is sufficient to induce muscle hypertrophy.
A major downstream effect of the PI3K/Akt pathway is the activation of the Mammalian Target of Rapamycin (mTOR) pathway. mTOR is the master regulator of protein synthesis, and its activation leads to increased production of cellular proteins and subsequent muscle cell growth, or hypertrophy.
Beyond stimulating synthesis, IGF-1 signaling also inhibits the breakdown of muscle protein. The Akt pathway suppresses the activity of FoxO transcription factors, which activate genes that code for E3 ubiquitin ligases—the machinery that tags muscle proteins for degradation. Furthermore, IGF-1 helps prevent muscle cell death by inhibiting apoptosis, ensuring that existing muscle fibers are maintained while new growth occurs.
Natural Influences on IGF-1 Production
Individuals can influence their natural IGF-1 levels through specific lifestyle and dietary adjustments, focusing on supporting the GH-IGF-1 axis. Intense resistance training is a powerful acute stimulus, as the mechanical stress and muscle microtrauma created by heavy lifting trigger the local, paracrine production of IGF-1 for repair and adaptation. High-intensity interval training also acutely increases the pulsatile release of Growth Hormone, which then stimulates the liver to produce more circulating IGF-1.
Proper nutrition is necessary to provide the building blocks and support the hormonal environment. Adequate protein intake, typically in the range of 1.6 to 2.2 grams per kilogram of body weight daily, supplies the amino acids required for protein synthesis and IGF-1 production. Specific amino acids, such as leucine, are particularly effective at directly activating the mTOR pathway, compounding the anabolic effect of IGF-1.
The quality and duration of sleep are also important for maintaining healthy IGF-1 levels. Growth Hormone release is pulsatile and peaks during the deep sleep cycles, which indirectly regulates the subsequent production of IGF-1. Chronic stress, which raises the catabolic hormone cortisol, can suppress both Growth Hormone and IGF-1 production, making stress management a factor in optimizing anabolic signaling. Certain nutrients, including zinc and magnesium, are also involved as cofactors in the complex metabolic processes that regulate the GH-IGF-1 axis.
Performance Enhancement and Safety Considerations
The potent anabolic effects of IGF-1 have made it a target for individuals seeking performance enhancement, but the use of synthetic versions carries significant risks and regulatory issues. IGF-1 is classified as a prohibited substance by the World Anti-Doping Agency (WADA) in all forms, reflecting its potential to enhance performance and its associated health risks. This ban applies to both in-competition and out-of-competition testing for athletes.
Commercially available oral supplements, such as sprays or lozenges claiming to contain IGF-1, are often ineffective because the peptide structure is broken down in the digestive tract before it can be absorbed. Synthetic IGF-1 injections, including analogs with modified half-lives, are sometimes misused in performance circles. Synthetic IGF-1 is legally a prescription drug and is not approved for use as a dietary supplement.
The most significant health risk associated with unregulated use stems from IGF-1’s powerful, non-selective growth-promoting properties. Epidemiological studies have consistently linked elevated circulating IGF-1 levels with an increased risk of developing certain cancers, including prostate, breast, and colorectal cancer. While IGF-1 may not cause cancer, it can accelerate the growth of existing or dormant tumors by promoting cell division and inhibiting programmed cell death.
Another acute safety concern with synthetic IGF-1 use is the risk of hypoglycemia, or dangerously low blood sugar. IGF-1 mimics some actions of insulin, promoting the uptake of glucose into cells. If injected without careful control of carbohydrate intake, this can lead to symptoms like dizziness, shakiness, and fatigue. Misuse can also lead to long-term side effects similar to Growth Hormone abuse, such as acromegaly, which involves the non-reversible enlargement of hands, feet, and internal organs.