Insulin-like Growth Factor 1 (IGF-1) is a polypeptide hormone structurally similar to insulin. Produced predominantly by the liver, its synthesis is directly stimulated by Growth Hormone (GH) released from the pituitary gland. IGF-1 acts as the primary mediator of GH’s effects, regulating growth and metabolism throughout the body.
IGF-1 maintains a constant presence in the bloodstream, mostly bound to specialized binding proteins (IGFBPs) that regulate its availability to tissues. Measuring circulating IGF-1 levels is often used as a reliable indicator of overall GH activity. Understanding how IGF-1 levels change over time is important, as it shapes the body’s development, repair processes, and long-term health.
The Primary Biological Role of IGF-1
IGF-1 functions as an anabolic agent, promoting the building up of tissues and complex molecules. It stimulates systemic body growth and exerts growth-promoting effects on nearly every cell type, including skeletal muscle, bone, cartilage, and nerve cells. Its primary action involves binding to the IGF-1 receptor (IGF1R), which initiates signaling pathways that drive cellular proliferation and survival.
The anabolic properties of IGF-1 are evident in its role stimulating muscle protein synthesis (generating new muscle tissue). It promotes the proliferation and differentiation of muscle satellite cells, which are necessary for muscle repair and hypertrophy following exercise. IGF-1 also supports bone health by stimulating the growth plates in long bones during development and helping to maintain bone density in adulthood.
Natural Fluctuation Across the Lifespan
The concentration of IGF-1 in the blood undergoes dramatic changes that correlate with developmental milestones. Levels are relatively low during infancy, gradually increasing through early childhood as the body begins its major growth phase. The most significant surge occurs during the pubertal growth spurt, reaching its peak in mid-adolescence.
This peak is driven by sex hormones, which stimulate a massive increase in GH secretion, causing a corresponding spike in IGF-1 that facilitates rapid skeletal and tissue growth. After puberty, IGF-1 levels drop sharply, sometimes by as much as 50% into early adulthood. They then begin a gradual decline across the remainder of the lifespan, a phenomenon referred to as somatopause.
Health Outcomes of Imbalanced Levels
Deviations from the normal, age-specific range of IGF-1 can lead to pathological health outcomes. Chronically low IGF-1 levels, often resulting from Growth Hormone Deficiency (GHD), have distinct consequences depending on the age of onset. In children, GHD results in stunted growth and short stature, as IGF-1 is necessary for growth plate development.
In adults, low IGF-1 is associated with poor body composition (reduced lean muscle mass and increased body fat), fatigue, and decreased bone density. Low IGF-1 levels are also associated with an increased risk of cardiovascular disease and may contribute to type 2 diabetes. Conversely, high IGF-1 levels are associated with Acromegaly in adults, where excessive GH production leads to the overgrowth of hands, feet, and facial features.
Chronically elevated IGF-1 is linked to an increased risk for certain malignancies, including prostate, colorectal, and breast cancers. The hormone’s cell proliferation and anti-apoptotic properties can promote the survival and growth of malignant cells. Research indicates a U-shaped relationship between IGF-1 and all-cause mortality: both very high and very low levels increase risk, while a mid-range concentration is associated with the best health outcomes.
Lifestyle Factors That Influence IGF-1
While age dictates the general trajectory of IGF-1 levels, lifestyle choices can modulate this hormone’s concentration. Dietary intake is a factor, with protein consumption shown to promote IGF-1 expression. High-protein meals can lead to a measurable increase in IGF-1 concentration 24 hours after ingestion.
Severe calorie restriction or malnutrition has the opposite effect, often leading to a reduction in IGF-1 levels. Physical activity is a regulator, with acute bouts of resistance training and high-intensity interval training (HIIT) causing an immediate elevation in IGF-1 concentration. This exercise-induced spike mobilizes resources for muscle repair and regeneration.
Sleep quality also plays a direct role, as the pituitary gland releases the majority of its Growth Hormone during deep sleep stages. Since GH directly stimulates IGF-1 production, ensuring adequate sleep supports healthy IGF-1 levels.