What is IGF-1?
IGF-1 stands for "insulin-like growth factor 1." That is a mouthful, so here is the simple version. IGF-1 is a hormone. A hormone is just a chemical messenger that travels in your blood and tells parts of your body what to do.
IGF-1 carries a "grow and repair" message. It tells your cells to build and fix things — bone, muscle, and other tissue. It is the messenger that did a lot of the work back when you were a child actually getting taller.
IGF-1 does not act alone. It is the partner of another hormone called growth hormone, often shortened to GH. Growth hormone is made by a small gland at the base of your brain called the pituitary. When the pituitary releases growth hormone, that hormone travels to your liver, and the liver responds by making IGF-1. So the chain is simple: pituitary makes GH, GH tells the liver, the liver makes IGF-1, and IGF-1 carries the grow-and-repair message to the rest of your body. Because of that chain, your IGF-1 level is often used as a window onto how the whole growth-hormone system is behaving.
This matters for blood tests. Growth hormone comes out in quick bursts and disappears fast, which makes it hard to measure with one blood draw. IGF-1 is steadier — it stays at a fairly level amount through the day. So when a clinician wants a sense of how active this whole system is, IGF-1 is usually the easier and more reliable thing to measure.
Why do IGF-1 levels change with age?
IGF-1 changes with age because growth hormone changes with age, and IGF-1 follows growth hormone.
When you are a teenager going through your growth spurt, your pituitary is pumping out a lot of growth hormone. Your liver answers by making a lot of IGF-1. This is the peak. It is supposed to be high then, because that is when your body is doing the most building.
After that peak — somewhere in your late teens or twenties — the system quietly turns down. Your pituitary makes less growth hormone year after year, so your liver makes less IGF-1. The drop is gradual, not a cliff. One large population study put the average decline at about 15% every ten years. So a healthy 60-year-old simply has much less IGF-1 in their blood than a healthy 25-year-old, and that is completely normal.
The decline is also not perfectly even across the decades. In one population study that mapped IGF-1 across adulthood, the steepest drop happened roughly between ages 21 and 50, after which the level tended to flatten into a plateau rather than keep falling at the same pace. So the biggest year-to-year changes are often earlier in adult life than people expect, and two adults who are both "older" may sit closer together than a young adult and a middle-aged one do.
This is the single most important idea on this page. A low IGF-1 reading is not automatically a problem. A number that would look low for a young adult can be perfectly normal for an older adult. That is exactly why a result has to be compared against other people of the same age, not against one fixed number for everyone.
What counts as a "normal" IGF-1 level?
Here is the honest answer most charts skip: there is no single normal IGF-1 number that works for everyone. "Normal" is a range, and the range slides down as you get older.
The pattern is the part worth remembering. IGF-1 is highest in your teens and twenties, and the normal range there sits high. By middle age the normal range has moved lower. In your sixties and beyond it is lower still. So a healthy result for a 25-year-old and a healthy result for a 65-year-old can look very different, and both are fine for their age.
It also depends a little on your sex. Studies that look at large groups of people find that men and women can sit at slightly different levels at certain ages, which is why many labs print separate ranges for men and women.
To make the pattern concrete, here is one real example from one specific laboratory — the University of Iowa's published reference ranges, measured on one specific machine. On that lab's test, a man around age 40 has a normal range of roughly 99 to 229 ng/mL ("ng/mL" is just the unit, like saying "miles per hour" for speed), while a man around age 60 has a normal range of roughly 61 to 191 ng/mL. You can see the whole range shift downward with age. But please read the next number as an example only, not as your number. The next section explains why your own lab's range can look quite different.
| Age (years) | Male (ng/mL) | Female (ng/mL) |
|---|---|---|
| 20 | 136–421 | 152–429 |
| 30 | 120–257 | 112–280 |
| 40 | 98.5–229 | 91.4–227 |
| 50 | 78.7–205 | 75.7–215 |
| 60 | 61.1–191 | 62–186 |
| 70 | 54.7–185 | 53.5–162 |
Why can't you compare results across labs?
This is the part that surprises people, so it is worth slowing down for.
IGF-1 is measured by a machine running a chemical test called an assay. An assay is just the specific method and chemistry a lab uses to detect how much IGF-1 is in your blood. The problem is that there is no single shared assay. Different labs use different machines from different makers, and those machines do not all read the same blood sample as the same number.
Researchers have tested this directly. In one study, scientists took blood from the same healthy people and ran it through six different commercial IGF-1 tests side by side. The low end of the normal range came out fairly similar across the tests, but the high end varied a lot from machine to machine. In plain terms: the very same blood could look normal on one lab's test and get flagged as high on another lab's test — without the person changing at all.
A good analogy is two bathroom scales. One reads five pounds heavier than the other. Your actual weight has not changed, but the number depends on which scale you stand on. IGF-1 assays are like that. The number only means something next to the range from that exact machine.
This has two practical consequences. First, the reference range printed on your own lab report is the one that matters for you — not a range you found online and not a friend's result from a different lab. Second, if your clinician is tracking your IGF-1 over time, they will usually want every test done by the same lab on the same assay, so that a change in the number reflects a real change in you and not just a change of machine.
Is a higher IGF-1 better — or worse?
Because IGF-1 is highest in youth and falls with age, it is tempting to assume that "more is better" — that a higher number means a more youthful, healthier body. The real picture is more nuanced than that, and worth understanding before you read your own result as a score to maximize.
At the high end, clearly elevated IGF-1 is a flag, not a prize. The body condition that produces a persistently high IGF-1 — acromegaly, where the pituitary makes too much growth hormone over years — causes real harm and needs treatment. Beyond that specific disease, large studies of ordinary people have found that those sitting in the upper part of the IGF-1 range carry a modestly higher risk of certain cancers. A widely cited 2004 Lancet analysis reported higher odds of prostate cancer (about 49% higher comparing the 75th with the 25th percentile) and premenopausal breast cancer (about 65% higher) in people with higher IGF-1 (PMID 15110491). That is an association across populations, not a verdict on any one person, and it does not mean a result near the top of your normal range is dangerous — but it is why "push IGF-1 as high as possible" is not sound health advice.
At the low end, a below-range result is not automatically bad either; as covered above, IGF-1 falls naturally with age and with things like undereating. The honest summary is that IGF-1 is not a simple "higher equals healthier" dial. Both ends carry their own meanings, the healthy zone is a range rather than a target, and what your number implies is a question for a clinician who can see the rest of your picture — not something to optimize from a chart.
How a clinician reads your result
A clinician does not look at an IGF-1 number on its own. They read it in context, and that context is what turns a number into useful information.
First they line your result up against the reference range for your age and sex, using the range from the exact lab that ran the test. A result inside that range is generally considered normal for someone like you. A result below or above it is a flag to look into, not a diagnosis by itself.
If your IGF-1 comes back lower than expected, a clinician thinks about the ordinary reasons before the rare ones. Getting older lowers it naturally. So can eating too little or losing a lot of weight, because the liver makes less IGF-1 when the body is short on fuel. Problems with the thyroid or the liver can lower it too. Only after weighing these would a clinician consider a true growth hormone deficiency, which usually calls for additional, more specific testing rather than a single blood draw.
If your IGF-1 comes back higher than expected, the main thing a clinician wants to rule out is a rare condition called acromegaly, where the body makes too much growth hormone over a long time. A clearly and substantially high IGF-1 is a reason to see a hormone specialist. A result just a little above the line, with no symptoms, is usually a "let us look at the whole picture" situation rather than an emergency.
The takeaway is steady and simple. One IGF-1 number is a clue, not a verdict. What it means depends on your age, your sex, the lab, your symptoms, your other lab results, and anything you are taking that affects this system. Putting those together is a clinician's job, not something to settle from an article.
Keeping track of IGF-1 with PeptidePanel
Nothing here is medical advice, and PeptidePanel does not sell, supply, prescribe, or recommend anything. Deciding what an IGF-1 result means, and what to do about it, belongs to a licensed clinician who can see your whole picture.
What PeptidePanel does is keep the record straight. IGF-1 is one of the markers it can track for you. It stores each result, charts the trend over time, and shows the number next to the reference range — so a slow drift across years is just as easy to see as a single out-of-range reading. If a clinician has you checking IGF-1 every so often, PeptidePanel is simply the organized notebook that keeps those results in one place and reminds you when the next one is due.