IGF-1 (Insulin-like Growth Factor 1): Levels, Reference Ranges & What They Mean

What Is IGF-1?

If your clinician has suggested checking your IGF-1, here is what that number is telling you. Insulin-like Growth Factor 1 (IGF-1) is a peptide hormone, a small protein-based hormone, made mostly by your liver in response to growth hormone (GH) released from the pituitary gland. GH comes out in short bursts that rise and fall hour to hour, while IGF-1 stays much steadier through the day. Because it holds steady, a single IGF-1 blood draw is the standard lab marker physicians use to estimate your overall GH activity, instead of measuring GH directly.

IGF-1 carries out most of the growth-promoting work of growth hormone. It supports tissue growth and repair, lean muscle maintenance, bone density, and the way your body processes fats and carbohydrates. IGF-1 production peaks naturally during puberty and declines steadily with age, which is one reason it is studied in healthy aging and longevity.

How IGF-1 Is Measured and Reported

IGF-1 is measured from a standard blood sample, usually reported in nanograms per milliliter (ng/mL). One detail matters here: IGF-1 levels depend strongly on age and, to a lesser degree, on sex. Levels are highest in adolescence and decline across adulthood. So your result should always be read against an age- and sex-matched reference range, not a single universal number.

Reference ranges are also assay-dependent. Different labs use different immunoassay platforms and calibration standards, so the “normal” range printed on your report can vary in a real way between labs. Many labs also report an IGF-1 z-score or standard deviation score (SDS), which shows how far your value sits from the average for your age and sex. That score is often more useful than the raw number when you are tracking results over time or comparing across labs.

Because of this variation, the most reliable approach is to follow your trend on the same assay and to have a clinician read your value against the reference range from the testing lab.

General Adult Reference Ranges

As a broad orientation only, adult IGF-1 commonly falls within roughly 50-300 ng/mL, with the expected range narrowing and shifting lower as you age. A value that is normal for a 25-year-old may be high for a 70-year-old, and the reverse is also true. Always defer to the age-specific range on your own lab report.

Symptoms and Who Should Consider Testing

IGF-1 testing is usually ordered when there is clinical suspicion of a growth hormone disorder, or as part of a wider hormonal and metabolic evaluation. A clinician may consider testing in adults who report:

• Persistent fatigue and reduced energy or stamina
• Loss of lean muscle mass or difficulty maintaining strength despite training
• Increased central body fat or unfavorable body-composition changes
• Reduced exercise tolerance or slower recovery
• Low mood, reduced motivation, or a lower sense of well-being
• Reduced bone density

Low IGF-1 can reflect adult growth hormone deficiency, but it may also occur with poor nutrition, significant calorie restriction, liver disease, poorly controlled diabetes, hypothyroidism, or systemic illness. Because the liver makes IGF-1, how well your liver works has a strong effect on your levels.

High IGF-1 calls for careful evaluation, because levels that stay elevated can be linked to excess growth hormone production (as seen in acromegaly), a medical condition that needs specialist assessment. Elevated IGF-1 is also why clinicians watch levels closely in anyone receiving growth-hormone-related therapy.

IGF-1 is rarely read on its own. It is usually evaluated alongside your clinical picture, and when a true GH disorder is suspected, your physician orders confirmatory dynamic testing (such as stimulation or suppression testing).

What Optimization Looks Like

For most adults, the goal is not to push IGF-1 as high as possible. Both extremes carry concerns, and very high IGF-1 has been a focus of safety discussion in aging research. A reasonable, physician-guided goal is to keep IGF-1 within a healthy, age-appropriate part of its reference range while addressing the factors that influence it.

Several well-established factors support healthy IGF-1 activity:

• Adequate protein and overall nutrition: IGF-1 falls with undernutrition and very low protein intake
• Resistance and regular exercise: supports lean mass and metabolic health
• Quality sleep: growth hormone is released largely during deep sleep
• Healthy liver function and metabolic control, including well-managed blood sugar and thyroid status

When a clinically confirmed deficiency is present, treatment is individualized and supervised by a qualified clinician, with IGF-1 used as one of the markers to guide and monitor therapy safely. The right target for you depends on your age, symptoms, overall health, and full lab panel.

Get Your Levels Evaluated

At ENNU Life in Louisville, IGF-1 can be reviewed as part of a full hormone, metabolic, and longevity evaluation, read in the context of your whole clinical picture rather than a single number.

Start your ENNU Life health assessment

Educational only, not medical advice; consult a licensed clinician. IGF-1 results are assay- and age-dependent and must be interpreted by a qualified healthcare professional alongside your symptoms, history, and other laboratory findings.