IGF-1 is a hormone produced primarily by the liver in response to growth hormone signaling. It mediates most of growth hormone's tissue effects (muscle synthesis, bone formation, cellular repair) and serves as a stable proxy for growth hormone status since growth hormone itself is released in pulses too variable to measure directly.
IGF-1 reflects growth hormone activity, nutritional status, and metabolic health. It declines with age (levels drop roughly 50% from age 25 to age 60) and age-stratified ranges are essential for meaningful interpretation. Low IGF-1 correlates with frailty, reduced muscle mass, and impaired recovery. However, extremely high IGF-1 is associated with increased cancer risk, so optimal levels balance both concerns. Protein intake, sleep quality, and resistance training all influence this marker.
Optimal IGF-1: 150-250 ng/mL.
Typically re-tested every 12 weeks.
Most adult results land inside a wide typical reference range, and the number means most in context, alongside your age, sex, nutrition, training load, sleep and other hormones. Results that sit well above or well below the range are worth discussing with a clinician rather than acting on alone.
IGF-1 is a protein hormone produced mainly by the liver in response to growth hormone, and it carries out much of growth hormone's effect on tissue growth, repair and metabolism.
The sequence is simple enough to follow. The pituitary gland releases growth hormone in pulses, weighted heavily toward deep sleep. Those pulses reach receptors on liver cells, which respond by producing IGF-1 and releasing it into the blood. Muscle, bone, cartilage and other tissues also make their own IGF-1 locally, where it acts close to the cells that produced it. Circulating IGF-1 then feeds back on the hypothalamus and pituitary and damps further growth hormone release, so the system regulates itself.
Once in circulation, almost all IGF-1 travels bound to carrier proteins, chiefly IGF binding protein 3 along with an acid-labile subunit. That binding is exactly why the marker is useful on a lab report. It stretches IGF-1's half-life from minutes to hours and smooths out the spikes and gaps of growth hormone secretion into a steady daytime signal.
The name comes from the receptor. The IGF-1 receptor closely resembles the insulin receptor, and IGF-1 has mild insulin-like effects on glucose handling, which is part of why it sits at the crossroads of growth and metabolism. At the cell, IGF-1 signalling promotes amino acid uptake and protein synthesis, supports cell division and differentiation, and slows programmed cell death. In plain terms, it is the body's build-and-repair messenger.
That stability is also why testing usually targets IGF-1 rather than growth hormone itself. A single growth hormone draw tells you very little, because you may have sampled a peak or a trough. An IGF-1 blood test gives an integrated picture of growth hormone activity over roughly the preceding day or so.
IGF-1 matters because growth hormone signalling touches muscle, bone, brain, skin and metabolic tissue, and IGF-1 is the readable proxy for how much of that signalling is actually reaching those tissues.
On the practical side, IGF-1 supports lean tissue maintenance, bone turnover and recovery from training or injury. It participates in glucose and lipid handling. It is also active in the nervous system, where it is involved in neuronal survival and repair processes.
The picture is broad and, importantly, mostly observational. Investigators have examined the relationship between circulating IGF-1 and blood pressure in adults[1], and the relationship between serum IGF-1 and ischaemic stroke[2]. Work on IGF-1 alongside inflammatory markers and delirium in surgical populations found associations that were inconsistent across studies[3]. IGF-1 levels have also been compared between people with multiple sclerosis and controls[4], and examined together with thyroid hormones in neurodevelopmental research[5].
Two cautions follow from that. First, association is not causation, and a marker that moves with illness may be a consequence rather than a cause. Second, IGF-1 does not behave as a simple more-is-better number. Neither the low end nor the high end is a goal in itself, which is why the useful question is where your result sits and what it sits next to, not how high you can push it.
A typical adult IGF-1 result falls inside a broad reference range, and FitScript applies a narrower optimization target inside it.
| Marker | Typical lab reference range | FitScript optimal range |
|---|---|---|
| IGF-1, serum | 100 to 300 ng/mL | 150 to 250 ng/mL |
In 2,791 healthy Chinese adults, IGF-1 fell steadily with age in both men and women, and the two sexes differed very little.[13]
| Sex | Age | 2.5th to 97.5th percentile (ng/mL) |
|---|---|---|
| Men | 20 to 24 | 140.8 to 451.4 |
| Men | 40 to 44 | 81.1 to 286.0 |
| Men | 60 to 64 | 65.4 to 230.8 |
| Men | 70 and over | 47.6 to 199.5 |
| Women | 20 to 24 | 141.2 to 476.9 |
| Women | 40 to 44 | 78.5 to 301.7 |
| Women | 60 to 64 | 46.5 to 210.4 |
| Women | 70 and over | 30.3 to 162.0 |
Selected age bands from the study are shown.[13] IGF-1 results depend on the assay, and labs often report them as an age-adjusted score as well as a number. Your own lab's printed range is the one to read your result against.
Reference ranges vary by laboratory, assay, age and sex, so the range printed on your own report is the one that applies to your result. FitScript's optimal range is an optimization target, not a diagnostic cut-off, and sitting slightly outside it is not a finding in itself.
Two more details are worth knowing. IGF-1 declines steadily with age in most people, peaking around adolescence and drifting down through adult life, which is why many labs report age-banded ranges rather than one adult band. And results may be reported in ng/mL or in nmol/L, and different assays do not always agree with one another, so tracking the trend in the same lab is far more informative than comparing single values across providers.
A high IGF-1 result means growth hormone signalling is running above the expected level for your age and sex, and the reason needs to be identified rather than assumed.
Many people with a modestly raised result notice nothing at all. When values are substantially and persistently elevated, people more often report changes they can see or feel, including rings and shoes becoming tighter, coarsening of facial features, joint aches, headaches, excessive sweating, tingling or numbness in the hands, and worsening snoring or disrupted sleep.
Common reasons for a high reading include normal physiology such as adolescence, pregnancy, or a growth phase in younger adults. Use of growth hormone or of compounds marketed as growth hormone secretagogues will raise it, as can assay variation between laboratories. A persistently high result that is not explained by age or physiology is the finding clinicians investigate for excess pituitary growth hormone production, usually with confirmatory testing rather than a single number.
On long-term health, high-normal and elevated IGF-1 has been studied in relation to insulin resistance and to a range of chronic disease outcomes, with mixed and largely observational findings. In mental health research, one meta-analysis reported significantly higher peripheral IGF-1 in people with major depressive disorder or bipolar disorder than in healthy controls[6], which again reflects association rather than cause.
The sensible reading is sequential. The value shows elevated growth hormone activity. That may reflect age, physiology, a supplement or medication, or something that needs a closer look. A result above your lab's range, especially a repeated one or one accompanied by the symptoms above, is worth discussing with a clinician promptly.
A low IGF-1 result means growth hormone signalling is running below the expected level for your age and sex, and it is most often a reflection of something else rather than a pituitary problem.
People with low readings commonly report fatigue, slow recovery from training, difficulty holding muscle or strength, lower exercise tolerance, poor sleep quality and low mood. None of those symptoms are specific to IGF-1, which is why the marker is interpreted alongside the rest of a hormone panel.
Frequent contributors include ageing, chronic under-eating or low energy availability, inadequate protein intake, poor or short sleep, high chronic stress load, uncontrolled diabetes, untreated hypothyroidism, chronic inflammation and liver disease, since the liver is the main production site. Less commonly, low IGF-1 reflects reduced pituitary growth hormone output, which requires dedicated testing to assess.
Serum IGF-1 has been examined in relation to ischaemic stroke[2] and investigated, with leptin, as a possible predictive biomarker for post-stroke depression[7]. A systematic review and meta-analysis reported that low serum IGF-1 was associated with an increased risk of rheumatoid arthritis[8]. Whether low IGF-1 contributes to these conditions or simply accompanies chronic illness and inflammation is not settled.
Again, observation then meaning then next step. The value shows reduced growth hormone activity. That may reflect nutrition, sleep, illness, thyroid status or liver function. A low result, particularly a repeated one or one paired with persistent symptoms, is worth reviewing with a clinician who can look at the full picture.
IGF-1 is relatively stable hour to hour, but nutrition, training, medication and illness can all move it, and small shifts between draws are normal.
Testing conditions. IGF-1 does not swing with meals the way glucose does, so strict fasting is often unnecessary, though individual labs set their own instructions and those should be followed. Acute illness, recent surgery and severe stress can depress the result. Because assays differ, repeat testing in the same laboratory makes trends far more meaningful.
Nutrition and body composition. Overall energy and protein intake are among the strongest everyday influences, and sustained under-eating tends to push IGF-1 down. Dietary pattern has been studied directly, with a systematic review and meta-analysis of randomized trials examining the effect of low-fat diets on IGF-1 and its binding proteins[9]. Supplements have been studied too, including a dose-response meta-analysis of clinical trials on lycopene supplementation and serum IGF-1[10].
Training. A systematic review and meta-analysis examined the effect of resistance training on serum IGF-1[11]. In practice, training load interacts with recovery and intake, and very high training volume layered on inadequate fuelling tends to move the marker in the opposite direction from what people expect.
Sleep. Growth hormone release concentrates in deep sleep, so chronically short or fragmented sleep plausibly reduces the downstream IGF-1 signal.
Medications and hormones. Several prescription medicines influence IGF-1. Oral oestrogen passes through the liver and tends to lower hepatic IGF-1 output, while a meta-analysis of randomized trials examined the effect of raloxifene on IGF-1 and IGFBP-3[12]. Thyroid hormone status, insulin and growth hormone therapy itself all affect the result. This article gives no doses, schedules or administration steps for any prescription therapy or peptide, and a licensed provider evaluates whether any such treatment is appropriate for a given person.
FitScript measures IGF-1 as part of its hormone lab panels, within a membership that covers 150+ biomarkers tested per year, so the marker is read against the rest of your endocrine and metabolic picture rather than on its own.
Results are interpreted by Atlas, the AI health advisor, which reads IGF-1 alongside thyroid, adrenal and sex hormone markers, inflammation, glucose regulation and your reported sleep, training and nutrition, then writes your FitScript from that biology. Because IGF-1 responds slowly to changes in habit, repeat testing over time is more useful than any single draw, and the comparison that matters is your own previous result in the same laboratory.
Where a result or a symptom pattern raises a clinical question, the answer is evaluation, not self-treatment. Growth-hormone-related therapies and peptides are experimental and clinician-gated, and a licensed provider decides whether any treatment is appropriate after reviewing the full case.
IGF-1 is interpreted most accurately inside a hormone panel, because the systems that raise and lower it overlap heavily.
DHEA-S gives a view of adrenal androgen output and, like IGF-1, tends to fall with age, so the two often move together. Cortisol reflects stress load, and sustained high cortisol is associated with the catabolic state that opposes IGF-1's build-and-repair signalling. Testosterone Total and Testosterone Free share IGF-1's territory in muscle, bone and recovery, and free testosterone depends on binding, which is why SHBG is measured with them and also tracks liver and insulin status, a pathway relevant to IGF-1 production. Pregnenolone sits upstream of several steroid hormones and helps frame where a broader hormonal shift may begin. All of these are tested together in FitScript's hormone lab panels, the Hormone Panel for him and the Hormone Panel for her, alongside thyroid and metabolic markers that influence IGF-1 production directly.
IGF-1 is the stable, measurable output of growth hormone signalling, mostly made by the liver and carried through the blood on binding proteins. A typical lab reference range runs around 100 to 300 ng/mL, it declines with age, and both high and low results carry information worth understanding rather than ignoring. The number is a starting point for a conversation about nutrition, sleep, training, thyroid function and liver health, not a verdict on any of them. This article is educational and is not medical advice, and any result outside your laboratory's range, or any symptom that concerns you, should be discussed with a clinician or licensed provider.
IGF-1 carries out much of growth hormone's effect on tissue. It promotes amino acid uptake and protein synthesis, supports cell growth and repair in muscle, bone and cartilage, slows programmed cell death, and has mild insulin-like effects on glucose handling. It is also active in the nervous system.
A typical adult serum reference range runs around 100 to 300 ng/mL, and FitScript's optimal range is 150 to 250 ng/mL. Ranges vary by laboratory, assay, age and sex, and levels fall steadily with age, so the band printed on your own report is the one that applies to your result.
Growth hormone is released in pulses, mostly during deep sleep, so a single random measurement may catch a peak or a trough and tell you very little. IGF-1 travels bound to carrier proteins and stays comparatively stable through the day, which makes it a far more practical read on growth hormone activity.
IGF-1 does not swing with meals the way glucose does, so strict fasting is often not required. Individual laboratories set their own preparation instructions, however, and those should be followed. If IGF-1 is drawn as part of a wider panel, fasting may be required for the other markers on it.
Common contributors include ageing, chronic under-eating or low protein intake, short or fragmented sleep, high stress load, untreated hypothyroidism, chronic inflammation, uncontrolled diabetes and liver disease, since the liver is the main production site. Less often it reflects reduced pituitary growth hormone output, which needs dedicated testing to assess.
Both may play a part, though how much either one shifts the result is uncertain. In practice, total energy and protein intake, training load and recovery all interact, so changes are rarely driven by one habit alone.
Yes. IGF-1 peaks around adolescence and drifts downward through adult life, which is why many laboratories report age-banded reference ranges. A result that would be low for a 25-year-old can be unremarkable at 60, and that is one reason the number is read in context rather than on its own.
Treat it as information, not a conclusion. Check whether age, physiology, a supplement or a medication explains it, confirm the result with a repeat test in the same laboratory, and note any symptoms such as ring or shoe tightness, joint aches, headaches or increased sweating. A persistently elevated result is worth discussing with a clinician promptly.
Several prescription medicines influence IGF-1, including oral oestrogen, raloxifene, thyroid hormone and growth hormone therapy, and growth-hormone-related peptides remain experimental and clinician-gated. No dose, schedule or administration guidance belongs in an article like this. A licensed provider evaluates whether any treatment is appropriate after reviewing the full case.