IGF-1 is one of the few longevity-adjacent biomarkers with a real clinical job. Endocrinologists use it to help investigate growth-hormone excess and, in narrower contexts, growth-hormone deficiency. The problem begins when a medically useful signal is repackaged as a general score for ageing. The evidence does not support that leap.
What IGF-1 actually measures
Insulin-like growth factor 1, usually shortened to IGF-1, is a hormone made largely in the liver in response to growth hormone. It helps mediate growth-hormone activity across tissues, which is why clinicians reach for it when they suspect too much or too little growth-hormone signalling. Unlike growth hormone itself, which is released in pulses and can vary sharply across the day, IGF-1 is a steadier downstream marker.
That steadiness is useful, but it is not the same as simplicity. IGF-1 varies with age, sex, nutritional status, liver function, kidney function, pregnancy, diabetes, assay method, and the laboratory’s reference range. A result that looks high or low on a private testing dashboard can mean something very different once it is interpreted against the right age-adjusted range and clinical picture.
This is why IGF-1 belongs in the same mental category as ApoB, HbA1c, or urine ACR: a useful biological measurement, not a verdict. It can point a clinician towards a problem. It cannot tell a healthy adult whether they are ageing well.
Where the test has the clearest clinical use
The strongest role for IGF-1 is in suspected acromegaly, the condition caused by chronic growth-hormone excess, usually from a pituitary adenoma. A recent international consensus statement in Pituitary describes IGF-1 as central to diagnosis and remission assessment, including the use of age-adjusted upper limits when clinical features are present (a 2024 consensus on acromegaly diagnosis and remission).
That does not mean a high IGF-1 result alone diagnoses acromegaly. Mayo Clinic’s clinical summary notes that high IGF-1 is an important marker, but also that it may be elevated in other settings, and that clinicians commonly confirm the picture with an oral glucose tolerance test and pituitary imaging when acromegaly is suspected (Mayo Clinic guidance on acromegaly diagnosis).
The practical point is straightforward. IGF-1 has real value when the pre-test probability is meaningful: enlarged hands or feet, changes in facial features, jaw changes, new spacing of teeth, headaches, sweating, sleep apnoea, carpal tunnel symptoms, glucose disturbance, or a known pituitary lesion. It is much less informative when ordered as part of a broad “biological age” panel in an otherwise well person.
Low IGF-1 is not automatically better
Longevity writing often treats growth signalling as something to suppress. The animal biology behind that idea is not imaginary. Lower growth-hormone and IGF-1 signalling is involved in several model organisms with extended lifespan. Human medicine, though, is not a direct replay of worm or mouse biology.
A 2022 meta-analysis in Aging Cell found a more complicated pattern in people: both low and high IGF-1 ranges were associated with higher all-cause mortality, with the lowest risk observed in a middle range rather than at the lowest end (a 2022 meta-analysis of IGF-1 ranges and all-cause mortality). That kind of U-shaped association is exactly why a single “lower is better” rule is too crude.
Low IGF-1 can also reflect poor nutrition, chronic illness, liver disease, pituitary disease, or frailty. In older adults, a low value may be a marker of vulnerability rather than a sign of successful ageing biology. The result may be useful, but only after the obvious question is asked: what clinical state produced it?
High IGF-1 needs context, not panic
High IGF-1 deserves attention because chronic growth-hormone excess is not benign. Untreated acromegaly can affect the cardiovascular system, metabolism, joints, soft tissues, sleep, and cancer risk. When symptoms point in that direction, IGF-1 is a legitimate entry point into proper endocrine assessment.
At the population level, the cancer signal is also real but not clean enough for personal scoring. A large prospective study reported that people at both low and high circulating IGF-1 levels had increased risks for some cancer-related outcomes, depending on the endpoint and cancer type (a 2023 population study of IGF-1 and cancer morbidity and mortality). That does not turn IGF-1 into a cancer screening test. It means the pathway is biologically relevant and still clinically messy.
The distinction matters. A biomarker can be associated with risk and still be a poor tool for individual prediction. For most adults, age, smoking status, family history, blood pressure, ApoB, diabetes status, kidney function, and established screening programmes are more actionable than a one-off IGF-1 result.
Why one result is easy to misread
IGF-1 interpretation depends on the reference interval used by the laboratory. Assays are not perfectly interchangeable, and the expected range falls with age. A 28-year-old and a 68-year-old should not be judged against the same biological expectation.
Nutrition can also move the number. Severe energy restriction, low protein intake, major illness, and liver dysfunction may lower IGF-1. Pregnancy, delayed puberty, diabetes, kidney disease, and some endocrine states may complicate a high result. That is why endocrinologists tend to repeat unexpected results and interpret them alongside symptoms, medication history, physical examination, and, when relevant, other pituitary hormones.
A 2024 review in the Journal of Clinical Medicine makes a similar point from the low-IGF-1 side: adult growth-hormone deficiency is difficult to diagnose from symptoms alone, and formal diagnosis relies on appropriate clinical context and growth-hormone stimulation testing, not simply on an isolated IGF-1 value (a 2024 review of adult growth-hormone deficiency).
Who might reasonably discuss testing
IGF-1 testing is most defensible when there is a specific endocrine question. That includes suspected acromegaly, known pituitary disease, follow-up after treatment for acromegaly, or specialist evaluation of possible adult growth-hormone deficiency. It may also be part of broader pituitary work-up after certain brain tumours, surgery, radiotherapy, traumatic brain injury, or hypothalamic-pituitary disease.
It is less defensible as a routine annual longevity screen. A healthy person can receive an abnormal-looking number, find alarming language online, and then spend weeks chasing a result that may be assay noise, age-range mismatch, or a non-specific response to another condition. Testing is not neutral when the result has no clear decision attached to it.
What this means in practice
- Do not treat IGF-1 as a biological-age score. It is a growth-hormone pathway marker with specific endocrine uses.
- If IGF-1 is high, interpret it against age-adjusted laboratory ranges and symptoms, not against internet “optimal” ranges.
- If acromegaly symptoms are present, discuss the result with an endocrinologist rather than repeating private panels.
- If IGF-1 is low, ask what might be driving it: nutrition, liver health, chronic illness, pituitary history, or frailty.
- Avoid using IGF-1 alone to justify growth-hormone treatment, aggressive protein restriction, or anti-ageing protocols.
- When the result is unexpected, repeat testing through the same laboratory or a clinician-directed pathway is often more informative than reacting to a single value.
What we don’t know
We do not know how to use IGF-1 as a personal longevity target in otherwise healthy adults. Observational studies can identify associations, but they cannot prove that deliberately moving someone’s IGF-1 up or down will improve lifespan, cancer outcomes, cardiovascular risk, or quality of life.
We also do not have a universal “best” IGF-1 range that applies across age, sex, health status, diet, and assay platform. The middle of a population-risk curve is not automatically a treatment target. Nor is a value that looks favourable in animal longevity research necessarily favourable for an older human with low muscle mass, poor appetite, or chronic disease.
IGF-1 is a serious marker in the right clinical setting. Its mistake is being promoted as a simple longevity dial. The better use is narrower and more useful: ask the endocrine question first, then decide whether the test can answer it.
Photo: National Cancer Institute on Unsplash.