Insulin-like Growth Factor 1 (IGF-1) is a polypeptide hormone similar in structure to insulin. It plays a broad role in various bodily functions, from growth and development to cellular maintenance.
What is IGF-1?
IGF-1 is a peptide hormone that shares structural similarities with insulin, including an A and B chain connected by disulfide bonds. While it can bind to the insulin receptor, it primarily acts through its own specific receptor, the IGF-1 receptor (IGF-1R).
The liver is the primary site of IGF-1 synthesis, a process largely stimulated by growth hormone (GH) released from the pituitary gland. Once produced, IGF-1 circulates throughout the bloodstream, with about 99% of it bound to specific binding proteins, particularly IGFBP-3. These binding proteins help modulate the availability and activity of free IGF-1 in the body.
IGF-1 is present in nearly every tissue and cell, reflecting its widespread influence on biological processes. It acts both systemically as an endocrine hormone and locally within tissues as a paracrine or autocrine factor.
Key Biological Roles
IGF-1 promotes growth and development, especially during childhood and adolescence, by mediating many of growth hormone’s effects. It stimulates the increase in both cell size and number in most tissues, including bone and muscle. IGF-1 levels typically rise during childhood and peak during puberty, aligning with periods of rapid growth.
Beyond growth, IGF-1 is involved in cellular differentiation and repair throughout life. It stimulates cell division and aids in the regeneration of damaged tissues, supporting wound healing, muscle repair, and the proliferation of muscle stem cells.
IGF-1 also influences metabolism, affecting how cells utilize glucose and synthesize proteins. It stimulates glucose uptake and utilization by cells, similar to insulin in modulating blood sugar. Additionally, IGF-1 promotes protein synthesis and can reduce protein breakdown, contributing to maintaining and building muscle mass.
The nervous system also benefits from IGF-1’s actions, as it functions as a neurotrophic factor. IGF-1 supports the survival and differentiation of neurons and influences neural development. Studies indicate that IGF-1 impacts brain size, neuronal cell number, and myelination, the formation of the protective sheath around nerve fibers.
Influencing IGF-1 Levels
IGF-1 levels fluctuate throughout an individual’s lifespan, with age being a primary factor. Concentrations increase during childhood, peak around puberty, and then gradually decline with advancing age. This age-related decrease in IGF-1 signaling is a normal biological change.
Nutrition significantly impacts IGF-1 levels. Adequate protein intake is associated with higher IGF-1 concentrations. Overall caloric status also plays a role, as avoiding fasting and ensuring sufficient nutrient availability can help maintain IGF-1 levels.
Physical activity, particularly strenuous exercise, can stimulate growth hormone levels, which in turn influences IGF-1 production. High-intensity interval training, for instance, has been shown to increase IGF-1 levels. Adequate sleep also contributes to healthy hormonal balance, indirectly affecting IGF-1.
Because IGF-1 production is directly linked to growth hormone (GH) secretion, factors influencing GH will also affect IGF-1 levels. Other endocrine factors, an individual’s genetic makeup, and chronic stress can also contribute to variations in IGF-1 concentrations.
IGF-1 and Health Conditions
Both elevated and low IGF-1 levels are associated with various health conditions. Elevated IGF-1 concentrations have been linked to an increased risk for certain types of cancer, including breast, prostate, and colon cancer. These are associations, not direct causation, and research continues to explore these complex relationships. Conditions like acromegaly, characterized by excessive growth hormone production, also result in abnormally high IGF-1 levels, leading to enlarged hands, feet, and facial features.
Conversely, low IGF-1 levels are often seen in individuals with growth hormone deficiency, which can result in growth deficiencies and short stature in children. Certain chronic diseases, such as liver disease and uncontrolled diabetes mellitus, can also lead to reduced IGF-1 concentrations. Malnutrition and prolonged fasting are also associated with lower IGF-1.
The aging-related decline in IGF-1, sometimes referred to as somatopause, can contribute to decreased muscle mass and neuronal loss. Low IGF-1 levels have also been linked to metabolic syndrome, a cluster of conditions including high blood pressure, high cholesterol, and abdominal fat, which collectively increase the risk of heart disease and type 2 diabetes.
Considerations for IGF-1 Use
In medical contexts, synthetic forms of IGF-1, such as mecasermin, are used to treat specific conditions like severe IGF-1 deficiency in children who are not growing as expected. These applications are carefully monitored by healthcare professionals.
Outside of medical supervision, IGF-1 products are sometimes marketed as supplements for purposes like muscle growth, anti-aging, or performance enhancement. These unregulated products lack scientific validation and pose potential safety concerns.
Unmonitored use of IGF-1 can lead to various side effects. These may include hypoglycemia (low blood sugar), which can be particularly dangerous, as well as joint pain, swelling, and nerve issues like Bell’s palsy. The long-term impact and safety of such unregulated use are not well established.
Many sports organizations prohibit the use of IGF-1 as a performance-enhancing substance. Given the potential for adverse effects and lack of regulation, consulting a healthcare professional is advisable before considering any form of IGF-1 supplementation.