Insulin-Like Growth Factor 1 (IGF-1)

These age bands are illustrative and vary by lab and assay; population data from the VARIETE cohort show the underlying slide, from roughly 374 ng/mL around age 18 to about 93 ng/mL after age 70. The point isn't the exact edges. It's that IGF-1 has to be read against your age, because the silo you're measuring is smaller at 60 than it was at 20. MedlinePlus describes the same lifespan arc: low in childhood, peaking through puberty, declining across adult life. A lab that prints one adult range and flags everything below it will mislabel a lot of healthy older adults.

A genuinely low IGF-1 (low for your age, not low against a young-adult cutoff) points toward the silo being underfed. The grain trucks aren't arriving, or the silo can't use what arrives. MedlinePlus links lower-than-normal levels to growth hormone deficiency or to insensitivity to GH, as in the rare Laron syndrome, where the body produces growth hormone but can't respond to it.

The catch is that one low reading proves little. The Endocrine Society is explicit that a single IGF-1 has poor diagnostic accuracy for growth hormone deficiency, and a normal value does not rule it out. So a low result is a reason to look further with dedicated testing, usually alongside other pituitary hormones, not a diagnosis on its own. If your level is low and you feel fine, that combination is common and frequently just reflects your age. The number that worries a 30-year-old can be the expected reading at 65.

A high IGF-1 is the overfilled silo, and at the dramatic end it has a clear culprit. MedlinePlus attributes elevated levels to gigantism in children and acromegaly in adults, most often driven by a pituitary tumor pumping out excess growth hormone. This is exactly where IGF-1 proves its value as a proxy: because growth hormone is too pulsatile to pin down in one draw, the Endocrine Society makes IGF-1 the first-line test for acromegaly and, in someone with typical features, treats a value above 1.3 times the age-specific upper limit of normal as confirmatory, with no random GH level required.

The harder message is for people chasing a high number on purpose. The idea that a higher IGF-1 is better, that more buys muscle and slows aging, runs into the data head-on. The relationship between IGF-1 and death is U-shaped: both the lowest and the highest levels carry higher mortality. In the EPIC-Heidelberg case-cohort, people at both extremes faced raised risk of dying from cancer, cardiovascular disease, and all causes, and higher IGF-1 specifically tracked with breast cancer (hazard ratio 1.25) and prostate cancer (hazard ratio 1.31). A meta-analysis pooling 19 studies and more than 30,000 participants found the same two-sided curve for all-cause mortality. These are observational associations, not proof that IGF-1 causes the harm, but they dismantle the "higher is healthier" story. There's a middle of the silo, not a level you keep topping up.

IGF-1 rarely travels alone on a lab order. It usually rides with the rest of the pituitary's output, so reading it next to its neighbors matters. See how the hormone panel frames the supporting cast, and the guide to reading a hormone panel for how clinicians weigh one hormone against another. When the pituitary is in question, IGF-1 sits alongside markers like ACTH, prolactin, cortisol, and DHEA-S, each a different window onto the same gland.

Because the silo level shifts so slowly and so predictably with age, a single IGF-1 is a snapshot of a moving target read against your own age-adjusted baseline. One convenience helps here: unlike the restless hormone it stands in for, IGF-1 holds steady through the day, so when you schedule the draw barely changes the result. A number that's stable for your age is reassurance; one that climbs or falls against the expected slide is the signal worth a doctor's attention.