IGF-1 is the stable messenger of growth hormone, driving growth in youth and tissue repair in adults. Very high levels define acromegaly, while the longevity debate argues over whether low-normal is a feature or a bug of aging.
Standard range versus optimal range
| Framework | IGF-1 value | Source |
|---|---|---|
| Interpretation | always age- and sex-adjusted | Endocrine Society 2014 |
| Acromegaly screening | above age-adjusted range, confirm with GH suppression test | Endocrine Society 2014 |
| Healthy mid-adult, approximate | about 100-250 ng/mL | Common laboratory range |
When it runs high
A clearly elevated age-adjusted IGF-1 raises the suspicion of acromegaly, a growth hormone tumor syndrome causing enlarged hands, jaw growth, diabetes and heart disease. Confirmation requires a glucose suppression test.
- Growth hormone-secreting pituitary adenoma
- Pregnancy and puberty, physiological
- Recent growth hormone use
- Liver and kidney conditions altering clearance, modest effects
When it runs low
Low IGF-1 can reflect growth hormone deficiency, but far more often it reflects undernutrition, liver disease, poorly controlled diabetes, hypothyroidism or simply aging. A single low value is weak evidence on its own.
- Normal aging, the commonest cause
- Malnutrition and low protein intake
- Liver disease
- Hypothyroidism and poorly controlled diabetes
- True growth hormone deficiency, uncommon
Growth hormone’s readable proxy
Growth hormone pulses through the blood in bursts, gone within minutes, which makes it nearly unmeasurable for diagnosis. IGF-1, made by the liver in response, circulates stably all day, offering the practical window into the whole axis. The Endocrine Society guideline makes age- and sex-adjusted IGF-1 the first test for acromegaly and one pillar of diagnosing growth hormone deficiency.
The longevity tug-of-war
Here is the genuine scientific tension. Animal studies consistently link reduced IGF-1 signaling with longer lifespan, and human centenarian studies often find low-normal IGF-1. Yet in middle-aged and older adults, very low IGF-1 associates with frailty, fractures and cardiovascular mortality. The emerging synthesis is a U-curve, both extremes carry risk, and the optimum likely drifts downward with age. Growth hormone supplementation in healthy aging adults increases side effects without proven benefit, so the molecule is a marker to understand, not a target to hack.
Interpreting your number
Never read IGF-1 without the age column of the reference range, the same 150 that is low-normal at 25 is comfortably normal at 65. Fasting, illness, poor sleep and under-eating all depress it temporarily, so borderline results deserve a repeat in a fed, healthy state before any conclusion. Used this way it is a quiet integrator of nutritional and hormonal health rather than a pass-fail exam.
Related calculators
Related biomarkers TSH · Glucose