IGF-1 Normal Range by Age: How to Read Your Result

If you have ever stared at an IGF-1 lab result and felt a flicker of panic, you are not alone. The number that looks alarmingly low for a 19-year-old can be perfectly healthy for a 55-year-old, because IGF-1 is one of the few biomarkers whose “normal” is a moving target across your entire life. Here is the part most lab printouts bury in fine print: there is no single normal IGF-1 number, only a normal range for your specific age and sex.

What is the normal IGF-1 range by age?

IGF-1 peaks in adolescence (around age 15) and declines steadily with age. Typical adult ranges run roughly 180 to 780 ng/mL at ages 17 to 24, 114 to 400 ng/mL at 25 to 39, 90 to 360 ng/mL at 40 to 54, and 70 to 290 ng/mL after 54. Always interpret against your own lab’s age and sex chart.

Why does IGF-1 change so much with age?

IGF-1 (insulin-like growth factor 1) is the hormone that carries out most of the work of growth hormone (GH) in your body. According to MedlinePlus, clinicians measure IGF-1 rather than GH directly because GH spikes and crashes throughout the day, while IGF-1 stays stable, making it a far more reliable mirror of your GH status from a single blood draw.

The lifetime arc is well mapped. The largest study to date, a multicenter analysis of 15,014 people aged 0 to 94 published in The Journal of Clinical Endocrinology & Metabolism by Bidlingmaier and colleagues (2014), traced a clear pattern: IGF-1 dips right after birth, climbs to a sharp pubertal peak around age 15, then declines continuously through adulthood and old age. That decline is steep and continuous: the upper end of the healthy range can fall by roughly half between the late teens and the late thirties, then keep dropping into old age, as the age bands in the table below show.

This is why a teenager and a retiree can have wildly different IGF-1 numbers and both be completely healthy. The hormone is doing exactly what it is supposed to do at each stage of life.

What are the IGF-1 reference ranges for adults by age group?

Reference intervals differ by laboratory and by the assay used, so treat the figures below as a general map, not a verdict. These age bands reflect commonly cited adult ranges in nanograms per milliliter (ng/mL):

Notice how the ceiling collapses with each decade. An IGF-1 of 350 ng/mL would sit comfortably mid-range for a 20-year-old but would land near the very top of the range for someone in their forties. Context is everything.

Do men and women have different IGF-1 levels?

Yes, but the gap is modest. The Bidlingmaier multicenter study concluded that “the impact of gender is small, although across the lifespan, women have lower mean IGF-1 concentrations.” Some adult lab ranges reflect this with separate columns, for example roughly 115 to 307 ng/mL for men versus 88 to 246 ng/mL for women in certain assays. The takeaway: sex matters less than age, but a good lab report still breaks both out.

Ethnicity, body mass index, and nutrition also shift the numbers. A reference-range study in healthy Chinese adults found IGF-1 intervals (2.5th to 97.5th percentiles) running from about 103 to 288 ng/mL across ages 20 to 69, and the authors explicitly cautioned that regional, ethnic, and nutritional factors limit how well one population’s reference values transfer to another. This is the single most important reason to compare your result against your own lab’s chart rather than a number you found online.

What does a high IGF-1 level mean?

A persistently high IGF-1, above the range for your age, is the main screening flag for acromegaly in adults and gigantism in children, conditions usually driven by a benign pituitary tumor pumping out excess growth hormone (MedlinePlus). In adults, acromegaly thickens bones and softens tissues, producing enlarged hands and feet, coarsening facial features, and joint pain that creeps in over years. In children, the same excess lengthens bones and can produce unusual height.

One caution worth knowing: a single elevated IGF-1 is a screen, not a diagnosis. Clinical research has documented cases of high IGF-1 that did not confirm acromegaly on follow-up glucose-suppression testing, which is why endocrinologists confirm with additional tests before concluding anything.

What does a low IGF-1 level mean?

A low IGF-1, below the age-appropriate range, can signal growth hormone deficiency or insensitivity. In children, that may show up as stunted growth and delayed development. In adults, GH deficiency can contribute to fatigue, reduced muscle mass, and a lower sense of well-being. But low IGF-1 is not automatically a disease. Poor nutrition, fasting, liver disease, and uncontrolled diabetes can all depress it, and the natural age-related decline means a “low-looking” number in an older adult may simply be age-appropriate.

If you are exploring this in the context of GH or peptide therapies, it is worth understanding the broader hormone picture first. Our overview of peptides explained covers how growth-axis compounds are marketed and where the evidence actually stands.

How should you actually read your IGF-1 result?

Three rules cut through most of the confusion. First, find your age band and sex on the report and read your value against that line, never against a generic “normal.” Second, a result just outside the range is rarely an emergency by itself; trends and repeat testing matter more than a single draw. Third, IGF-1 is a screening tool, so an abnormal number is a reason to talk to a clinician, not a diagnosis you can make at your kitchen table.

Frequently asked questions

Is IGF-1 the same as growth hormone?

No. Growth hormone is released by the pituitary in pulses and fluctuates hour to hour. IGF-1 is produced mainly by the liver in response to GH and stays stable, which is why labs measure IGF-1 as a steady proxy for your GH status (MedlinePlus).

At what age does IGF-1 peak?

Around age 15, during puberty, based on the 15,014-person multicenter study in The Journal of Clinical Endocrinology & Metabolism. After that peak it declines continuously for the rest of life.

Why do lab ranges for IGF-1 differ so much?

Different laboratories use different assays and calibration standards, and reference populations vary by ethnicity, BMI, and nutrition. A Chinese adult reference study specifically warned that these factors limit cross-population comparison, which is why you should use your own lab’s chart.

Can lifestyle change my IGF-1 level?

Nutrition has a clear effect: fasting and protein-calorie restriction lower IGF-1, while adequate nutrition supports it. Chronic illness and liver function also influence the number. These factors are well documented, though IGF-1 should be interpreted as part of a full clinical picture rather than chased in isolation.

Does a low IGF-1 mean I am aging faster?

Not on its own. IGF-1 naturally falls with age in everyone, so a lower number in an older adult is usually expected, not a sign of accelerated aging. Interpreting it requires your age-specific range and clinical context.

This article is for general information only and is not medical advice. IGF-1 results must be interpreted by a qualified clinician using your specific lab’s reference ranges and your full health history. Consult your healthcare provider before making any decisions based on a lab result.