IGF-1
Also known as: Insulin-like Growth Factor 1, Somatomedin C
What Does IGF-1 Measure?
IGF-1 (Insulin-like Growth Factor 1), also called Somatomedin C, is a hormone produced primarily by the liver in response to stimulation by growth hormone (GH) released from the pituitary gland. A blood test measuring IGF-1 reflects the overall activity of the GH-IGF-1 axis, giving clinicians a stable, reliable snapshot of growth hormone status over time. Unlike growth hormone itself, which fluctuates dramatically throughout the day in pulses, IGF-1 levels remain relatively constant, making it a much more practical marker for assessing growth hormone sufficiency or excess.
Why Does IGF-1 Matter?
IGF-1 plays a central role in childhood growth and development, tissue repair, muscle maintenance, bone density, and metabolic regulation throughout life. In children, abnormal IGF-1 levels can signal growth disorders such as growth hormone deficiency or gigantism. In adults, IGF-1 is essential for maintaining lean muscle mass, bone strength, cognitive function, and metabolic health. Both very low and very high levels are clinically significant: low IGF-1 in adults is linked to increased risk of cardiovascular disease, osteoporosis, and reduced quality of life, while chronically elevated IGF-1 — particularly in conditions like acromegaly — is associated with increased risk of certain cancers, joint problems, and cardiovascular complications. Monitoring IGF-1 is also critical for managing patients on growth hormone therapy.
Normal Ranges
Males
Ages 18-25: 116-358 ng/mL; Ages 26-35: 100-303 ng/mL; Ages 36-50: 85-233 ng/mL; Ages 51-65: 60-200 ng/mL; Ages 65+: 55-185 ng/mL
Females
Ages 18-25: 107-367 ng/mL; Ages 26-35: 95-290 ng/mL; Ages 36-50: 80-225 ng/mL; Ages 51-65: 55-195 ng/mL; Ages 65+: 50-178 ng/mL
Children
Varies significantly by age and pubertal stage; typical ranges: ages 2-5: 17-248 ng/mL; ages 6-8: 88-474 ng/mL; peak during puberty (ages 12-15): 237-996 ng/mL
Causes of High Levels
- Acromegaly — a pituitary tumor secreting excess growth hormone in adults, leading to chronically elevated IGF-1
- Gigantism — excess growth hormone production in children before growth plates close, causing abnormal height increase
- Pituitary tumors (GH-secreting adenomas) that continuously stimulate IGF-1 production in the liver
- Obesity — higher insulin levels and adipose tissue activity can moderately elevate IGF-1 in some individuals
- Excessive growth hormone therapy or abuse of synthetic GH for bodybuilding or anti-aging purposes
- Insulin resistance and hyperinsulinemia, which can amplify IGF-1 signaling and elevate circulating levels
Causes of Low Levels
- Growth hormone deficiency (GHD) — insufficient pituitary GH secretion due to pituitary damage, tumors, or genetic conditions
- Malnutrition, prolonged fasting, or eating disorders such as anorexia nervosa, which suppress liver IGF-1 production
How to Improve Your IGF-1
Diet
- Ensure adequate protein intake of 1.2–2.0 grams per kilogram of body weight daily, as amino acids (especially leucine) are key stimulators of IGF-1 production
- Consume zinc-rich foods such as oysters, beef, pumpkin seeds, and legumes, as zinc deficiency impairs GH-IGF-1 signaling
- Include magnesium-rich foods like leafy greens, nuts, seeds, and dark chocolate, which support growth hormone pulsatility
- Eat a balanced diet with sufficient calories — severe caloric restriction dramatically suppresses IGF-1 regardless of protein intake
- Limit excessive alcohol consumption, as chronic alcohol intake impairs liver function and reduces IGF-1 synthesis
Supplements
- Zinc: 15–30 mg per day may support IGF-1 levels in those who are deficient; avoid excessive doses above 40 mg/day
- Vitamin D3: 1,000–4,000 IU per day — adequate vitamin D status is associated with healthier IGF-1 levels and GH axis function
- Magnesium glycinate or citrate: 200–400 mg per day to support hormonal regulation and sleep quality, which influences GH release
- Creatine monohydrate: 3–5 g per day combined with resistance training may modestly support IGF-1 and muscle anabolism
Related Biomarkers
Frequently Asked Questions
What does it mean if my IGF-1 is low as an adult?
Low IGF-1 in adults often indicates growth hormone deficiency, which can result from pituitary gland problems, chronic illness, poor nutrition, or simply aging. Symptoms may include increased body fat (especially around the abdomen), reduced muscle mass, fatigue, poor bone density, and reduced sense of wellbeing. A doctor will typically investigate further with GH stimulation tests and assess for treatable underlying causes before considering growth hormone replacement therapy.
Can high IGF-1 increase cancer risk?
Chronically elevated IGF-1 has been associated in some epidemiological studies with increased risk of certain cancers, including prostate, breast, and colorectal cancers, because IGF-1 promotes cell growth and inhibits programmed cell death (apoptosis). However, it is important to distinguish between pathologically elevated IGF-1 (as seen in acromegaly) and levels at the upper end of the normal range. Most research suggests that the concern applies primarily to levels well above the normal reference range sustained over long periods. Maintaining IGF-1 within the healthy normal range is the goal.
How is an IGF-1 blood test performed and do I need to fast?
An IGF-1 test is a simple blood draw, usually from a vein in the arm. Unlike growth hormone testing, IGF-1 does not require special timing because levels are relatively stable throughout the day. Fasting is generally not required, but your doctor may have specific instructions based on other tests being ordered at the same time. Results are usually available within a few days.