IGF-1
Insulin-like growth factor – marker for the GH axis and biological aging
Also known as
Definition
Insulin-like growth factor 1 (IGF-1, formerly somatomedin C) is produced mainly in the liver in response to growth hormone (GH). IGF-1 mediates the anabolic effects of GH on muscles, bone, and organs. Levels are strongly age-dependent (peak in puberty, steady decline from age 30) and serve as a marker of GH/IGF-1 axis activity.
| Parameter | Value |
|---|---|
| Unit | nmol/l (ng/ml) |
| Reference Range | Strongly age-dependent. Adults 30–40 yr: 15–40 nmol/l (115–307 ng/ml) | 50–60 yr: 10–28 nmol/l (77–215 ng/ml). The value is interpreted using the age-adjusted SDS score. |
Agree on your personal target range with your doctor.
Conversion: 1 nmol/l = 7.65 ng/ml. US labs report in ng/ml (strongly age-dependent; e.g., 40-year-old man: ~90–250 ng/ml).
↓ What a low value means
Low IGF-1 suggests growth hormone deficiency (pituitary insufficiency), severe liver disease (site of IGF-1 synthesis), malnutrition, chronic inflammation, or marked dietary restriction (fasting). Associated with: muscle wasting (sarcopenia), bone density loss, increased fracture risk, fatigue, and cardiovascular risk.
↑ What a high value means
Elevated IGF-1 (> 2 SDS above age median) occurs with acromegaly (GH-secreting pituitary tumor) or excessive GH/IGF-1 supplementation. Chronically high IGF-1 levels are epidemiologically associated with increased risk of breast, prostate, and colorectal cancer.
✓ What can influence this value
The IGF-1 value is influenced by age, liver function, nutritional status, illnesses, and the activity of the growth hormone axis. A high intake of protein and dairy products can raise the value, while intermittent fasting and caloric restriction can lower it. Resistance training stimulates the GH/IGF-1 axis. Growth hormone is released pulsatilely, mainly at night during deep sleep; sleep deprivation can lower the value.
When to test
As a marker of GH axis activity, acromegaly screening, suspected sarcopenia, pituitary disease, or to monitor GH therapy. It is interpreted using an age-corrected reference range.
Frequently asked questions
How is a high IGF-1 level linked to longevity? +
It is complex. In the short to medium term, IGF-1 supports muscle preservation and physical capacity. Chronically elevated levels (top quartile) are associated with increased cancer risk in epidemiological studies. Centenarian studies (longevity research) sometimes show lower IGF-1 in the oldest old. The laboratory's age-corrected reference range applies; the doctor makes the assessment.
Is IGF-1 linked to diet? +
Yes. Milk products, animal protein, and total calorie intake raise IGF-1. A plant-based diet and caloric restriction lower IGF-1 (EPIC study). Intermittent fasting (> 24 hours) significantly lowers IGF-1. Resistance training transiently raises IGF-1 pulsatilely through GH release.
What is the difference between IGF-1 and growth hormone (GH)? +
GH is released pulsatilely from the pituitary (half-life ~20 min) and is difficult to measure reliably in blood. IGF-1 is produced in the liver as a stable response to GH (half-life ~12–15 hours) and reflects average GH activity over the preceding hours to days. IGF-1 is therefore the better clinical marker for the GH axis.
How does sleep affect IGF-1 levels? +
Growth hormone is released mainly during the first sleep cycles in deep sleep (NREM sleep) — ~80% of daily GH production occurs during the night. Sleep deprivation significantly reduces GH pulses and, over time, also lowers IGF-1.
IGF-1
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.