IGF-1 Test · Blood

If you could see a single number that captures how aggressively your body is building, repairing, and growing, IGF-1 (insulin-like growth factor 1) would be that number. It is tied to your risk of heart disease, several cancers, stroke, dementia, and how quickly you age. What makes it unusual is that the risk does not move in one direction. Both low and high levels are linked to worse outcomes, and the "sweet spot" shifts as you get older.

Standard blood panels do not include IGF-1. You can have perfectly normal cholesterol, blood sugar, and liver enzymes while your IGF-1 sits at a level associated with meaningfully higher risk. Knowing your number gives you a read on a biological system that most routine testing ignores entirely.

What IGF-1 Actually Tells You

IGF-1 is a small protein, 70 amino acids long, that your liver releases into the bloodstream under the direction of growth hormone (GH). About 75 to 90% of circulating IGF-1 comes from the liver. Nearly all of it travels bound to carrier proteins, especially one called IGFBP-3 (insulin-like growth factor binding protein 3), which extends its lifespan in the blood and controls how much of it reaches your tissues.

Because growth hormone itself surges in short bursts throughout the day and is hard to measure reliably with a single blood draw, IGF-1 serves as a steadier, more dependable stand-in. Think of growth hormone as a flickering signal and IGF-1 as the average brightness over the whole day. A single IGF-1 measurement captures what your growth hormone axis has been doing over days to weeks, not just what happened in the hour before your blood was drawn.

Clinically, your IGF-1 level reflects three things at once: how active your growth hormone system is, how well your liver is functioning as a protein factory, and your body's overall nutritional status and tissue-building capacity. A low number can signal growth hormone deficiency, liver disease, or chronic undernutrition. A high number can point to growth hormone excess (a condition called acromegaly, where the body produces too much growth hormone) or a metabolic environment that may be fueling unwanted cell growth.

The U-Shaped Risk Curve

The most striking pattern in the IGF-1 research is that risk does not simply rise or fall with the number. It forms a U shape. A meta-analysis pooling 19 prospective studies with over 30,000 adults found that people with IGF-1 in the mid-range, roughly 120 to 160 ng/mL, had the lowest risk of dying from any cause. People with levels below that range were about 33% more likely to die during follow-up, and people with levels above it were about 23% more likely to die, compared to the mid-range group.

An earlier meta-analysis of 12 cohorts with nearly 15,000 participants confirmed the same shape. Compared to the middle of the distribution, those at the 10th percentile (low end) had about 56% higher all-cause mortality, and those at the 90th percentile (high end) had about 29% higher mortality. This U-shaped pattern held for both cancer deaths and cardiovascular deaths.

This means IGF-1 is not a "lower is better" or "higher is better" marker. It is a balance marker. The goal is to land in the middle and stay there, and the right middle shifts with your age.

How Age Changes the Picture

A large analysis of over 440,000 UK Biobank participants revealed that the relationship between IGF-1 and disease changes as you age. Scientists call this pattern antagonistic pleiotropy, meaning a biological trait that protects you when young can become harmful when old. In younger adults, higher IGF-1 tends to be protective, supporting tissue repair, bone density, and metabolic health. In older adults, higher IGF-1 shifts toward being harmful, associated with increased risk of cancer, cardiovascular disease, and death.

This has a practical implication: a level that looks reassuringly normal at 35 might represent a very different risk profile at 65. Interpreting IGF-1 without considering your age will lead you to the wrong conclusion. Any lab result you receive should be compared against age-specific and sex-specific reference ranges, not a single "normal" cutoff.

Heart Disease and Stroke

A study of 394,082 UK Biobank adults followed for a median of 11.6 years found U-shaped associations between IGF-1 and nearly every cardiovascular endpoint. Compared to the middle fifth of IGF-1 levels, those in the lowest fifth had about 13% higher risk of cardiovascular disease overall, about 19% higher risk of heart failure, and about 15% higher risk of stroke. Those in the highest fifth also had elevated risk, roughly 6% higher for cardiovascular disease overall, 10% for heart failure, and 11% for heart attack.

A separate meta-analysis of ischemic stroke (stroke caused by a blocked blood vessel in the brain) specifically found that higher IGF-1 was associated with lower stroke incidence and better functional recovery after a stroke, suggesting that the protective floor for vascular health sits somewhere in the mid-to-upper normal range rather than at the bottom.

In an older study of 1,185 adults aged 51 and older followed for 9 to 13 years, each 40 ng/mL drop in IGF-1 was associated with about 38% higher risk of dying from ischemic heart disease, even after adjusting for standard cardiovascular risk factors.

Cancer Risk

Where the heart and brain seem to benefit from having enough IGF-1, cancer risk rises with more of it. This makes biological sense: IGF-1 promotes cell growth and survival, which is exactly what tumors exploit.

A pooled analysis of 17 prospective studies including 4,790 breast cancer cases found that women in the highest fifth of IGF-1 had about 28% greater odds of developing breast cancer than those in the lowest fifth. This association was specific to estrogen receptor-positive (ER+) tumors, meaning cancers fueled by estrogen, and was not affected by menopausal status or IGFBP-3 levels.

For prostate cancer, a meta-analysis of individual participant data from over 10,500 cases found that men in the highest fifth of IGF-1 had about 29% higher odds of prostate cancer. In the Northern Sweden cohort, the association was strongest in men under 59 and in those who went on to develop advanced disease, where top-quartile IGF-1 was associated with roughly four-fold higher odds.

An analysis of over 412,000 UK Biobank participants found that for every 5 nmol/L higher IGF-1, risk increased for breast cancer (about 10%), prostate cancer (about 9%), and colorectal cancer (about 7%). Interestingly, higher IGF-1 was associated with lower risk of lung cancer (about 9% lower) and liver cancer (about 68% lower), likely because liver disease itself suppresses IGF-1 production.

Making Sense of the Contradictions

It may seem contradictory that low IGF-1 raises your risk of dying from heart disease while high IGF-1 raises your risk of certain cancers. The resolution is that IGF-1 is not a simple "good" or "bad" number. It is a biological snapshot: your level reflects what your body is doing biologically, and different biological states carry different risks for different diseases.

Low IGF-1 often signals poor liver function, undernutrition, or weakened tissue-building capacity, all of which make your cardiovascular system and brain more vulnerable. High IGF-1 signals vigorous growth promotion, which protects against degeneration but feeds the same cell-growth programs that cancers depend on. The mid-range represents the balance point where your body has enough repair capacity without excessive growth signaling. This is why the mortality data consistently shows a U shape rather than a straight line.

Brain Health

A UK Biobank analysis of 369,711 adults followed for a median of 12.6 years found U-shaped associations between IGF-1 and both dementia and stroke. The lowest dementia risk was at an IGF-1 concentration of about 18 nmol/L, and the lowest stroke risk at about 26 nmol/L. Higher IGF-1 was also linearly associated with increased risk of Parkinson's disease.

Higher IGF-1 was associated with larger volumes of white matter (the brain's wiring that connects different regions) and the hippocampus (the brain's memory center), and with fewer white matter hyperintensities (a marker of small vessel damage visible on brain imaging). In the Rotterdam Study, each standard-deviation increase in total IGF-1 was associated with about 35% lower odds of meaningful cognitive decline over roughly two years in older adults.

Despite these associations, a systematic review concluded that IGF-1 does not currently add reliable diagnostic value for predicting cognitive decline in aging. The relationship is real but not precise enough to use as a standalone brain health screen.

Liver Disease

Because the liver is the main source of circulating IGF-1, your level doubles as a rough gauge of liver function. In a study of 269 patients with cirrhosis (advanced scarring of the liver), lower IGF-1 independently predicted decompensation (when the scarred liver can no longer keep up with its basic functions), a dangerous complication called acute-on-chronic liver failure, and liver-related death. The test's ability to predict six-month liver-related death was strong, with a prediction accuracy score of 0.856 out of 1.0.

If you have known liver disease or risk factors for it (heavy alcohol use, fatty liver, hepatitis), a low IGF-1 adds information that standard liver enzymes may not capture, because enzymes reflect damage while IGF-1 reflects the liver's remaining capacity to build proteins.

Reference Ranges

IGF-1 reference ranges are always specific to age, sex, and the laboratory method used. Different testing platforms give systematically different numbers for the same blood sample, which means a result from one lab cannot be directly compared to a result from a different lab using a different method. The ranges below are drawn from large population studies and are meant as orientation, not absolute targets. Always compare your results within the same lab over time.

A multicenter study of over 15,000 subjects across 12 cohorts (ages 0 to 94, using a standardized automated laboratory method calibrated to the WHO 02/254 reference standard) found the following approximate adult ranges for the 2.5th to 97.5th percentile:

From a longevity and mortality perspective, a meta-analysis of 19 prospective cohorts identified 120 to 160 ng/mL as the range associated with the lowest all-cause mortality in adults. This is not a guideline-endorsed target, but it is the most specific human data available for framing an "optimal" zone. Values below 120 or above 160 ng/mL were both associated with higher risk, though the exact risk depends on your age, sex, and health context.

For clinical diagnosis: an IGF-1 below the 2.5th percentile (or below negative 2 standard deviations for your age and sex) raises suspicion for growth hormone deficiency. An IGF-1 above the 97.5th percentile raises suspicion for acromegaly. These cutoffs are specific to the testing platform used and should be interpreted by your lab's reference intervals.

When Results Can Be Misleading

Several common situations can push your IGF-1 reading away from its true baseline, leading to a result that looks abnormal when your underlying biology is fine, or looks normal when it is not.

• Acute illness or recent surgery: Serious illness suppresses IGF-1 through a pattern of growth hormone resistance. Testing during or shortly after hospitalization, infection, or surgery will give an artificially low number that does not reflect your steady-state level.
• Oral estrogens: Birth control pills and oral hormone replacement therapy reduce the liver's sensitivity to growth hormone, which lowers IGF-1 production. This can mask acromegaly or falsely suggest growth hormone deficiency. Switching to a skin-patch form of estrogen or stopping oral estrogen for about three months before retesting is recommended if the result seems discordant with your clinical picture.
• Severe caloric restriction or malnutrition: Prolonged fasting or very low calorie intake can lower IGF-1 by 30 ng/mL or more. If you are actively dieting, fasting, or underweight, a low result may reflect nutritional status rather than a growth hormone problem.
• Liver or kidney disease: Because the liver produces most circulating IGF-1, chronic liver disease can dramatically lower your level. Advanced kidney disease also alters IGF-1 metabolism. In either case, the low number reflects organ dysfunction, not necessarily a primary growth hormone issue.
• Metformin: A meta-analysis of 11 randomized trials found no statistically significant overall effect of metformin on IGF-1. The direction of change varied by age, with slight decreases in younger populations and slight increases in adults. If you are taking metformin, a borderline IGF-1 result may not reflect your true underlying growth hormone status.

Differences between testing platforms are another source of confusion. A study comparing six commercial IGF-1 testing methods in the same group of 911 healthy adults found that the lower limits of normal were similar across methods, but the upper limits varied markedly. The same sample could be flagged as elevated on one platform and normal on another. This is why comparing results across different labs or testing methods is unreliable.