Somatomedin is the older name for insulin-like growth factor 1 (IGF-1), the substance that does much of growth hormone’s work, turning the hormone’s signal into actual growth of bones and tissues. Growth hormone mostly acts by prompting the body to make IGF-1, which then reaches growing tissues.1PubMed. The somatomedin hypothesis: 2001 The pituitary gland in the brain releases growth hormone in bursts, and tissues such as the liver respond by making IGF-1, which then tells cells to grow. Its effects reach beyond height, touching muscle, the brain, and even how fast the body ages, so the same molecule that helps a child grow is studied in adults for very different reasons.
Somatomedin Is Now Called IGF-1
The name changed as scientists learned what the molecule was. In 1957 researchers found a growth hormone-dependent substance in blood and called it “sulfation factor.”2Hormone Research in Paediatrics. The History of the Insulin-Like Growth Factor System In 1972 it was renamed “somatomedin,” meaning something that carries out growth hormone’s effects.3Hormone Research in Paediatrics. The History of the Insulin-Like Growth Factor System In 1976 two such substances were isolated from human blood and, because they resembled insulin in structure, were renamed insulin-like growth factors I and II.4Hormone Research in Paediatrics. The History of the Insulin-Like Growth Factor System The first of these is IGF-1.
The “insulin-like” part is literal. IGF-1’s shape closely resembles insulin’s, so it can nudge blood sugar down the way insulin does.
The older name still appears on some lab paperwork. “Somatomedin C” and “IGF-1” are the same test, since the “C” marked the version that later became IGF-1. Labs use different methods and reference ranges, so each number is best judged against its own lab’s range.
Growth was once thought to depend only on IGF-1 made in the liver and carried in the blood.5PubMed. The somatomedin hypothesis: 2001 But tissues such as bone and cartilage also make their own IGF-1, which acts right where it is produced.6PubMed Central. Autocrine and Paracrine Actions of IGF-I Signaling in Skeletal Development A related hormone, IGF-2, mainly drives growth before birth rather than after.7PubMed Central. Roles of Type 1 Insulin-Like Growth Factor (IGF) Receptor and IGF-II in Growth Regulation: Evidence From a Patient Carrying Both an 11p Paternal Duplication and 15q Deletion
How IGF-1 Makes Bones Grow Longer
Long bones grow at growth plates, bands of cartilage near each end that harden into bone after puberty. In animal studies, IGF-1 made locally in cartilage and bone matters more for bone development than the IGF-1 circulating in blood.8PubMed Central. Autocrine and Paracrine Actions of IGF-I Signaling in Skeletal Development It helps cartilage cells and bone-building cells grow, survive and mature.9PubMed Central. Autocrine and Paracrine Actions of IGF-I Signaling in Skeletal Development
Growth-plate cells are stacked in columns. They divide at one end of the column. Further along they swell to many times their size, and bone then forms on the scaffold those swollen cells leave behind. IGF-1 boosts both the dividing and the swelling.
Mouse experiments show how much depends on it. Without IGF-1 signaling, fewer growth-plate cells divide and more die off.10PubMed Central. IGF-1R Signaling in Chondrocytes Modulates Growth Plate Development by Interacting With the PTHrP/Ihh Pathway In mice lacking IGF-1, the final enlarged cartilage cells that bone builds upon were about 30% shorter.11PubMed. Igf1 promotes longitudinal bone growth by insulin-like actions augmenting chondrocyte hypertrophy12PubMed. Igf1 promotes longitudinal bone growth by insulin-like actions augmenting chondrocyte hypertrophy
Inside the cell, the process starts when IGF-1 docks onto its receptor on the cell surface and switches on chemical relays.13PubMed Central. The signaling landscape of insulin-like growth factor 1 One relay mainly keeps cells alive and growing, and the other mainly makes them divide and mature.14PubMed Central. Insulin-like growth factor receptor signaling in physiology and disease
Growth is not smooth or endless. At the plates it is steady in childhood, then speeds up during the puberty growth spurt, when hormone levels, including IGF-1, are higher. Late in puberty the plates thin out and fuse, so height gain slows and then stops. Doctors sometimes X-ray the hand and wrist to judge how much growing a child has left, because open plates show up on the image.
That fusion is also why adults stop getting taller even though they still make IGF-1. Once the plates have turned to solid bone, no cartilage is left for IGF-1 to stretch. In adults it shifts toward maintaining tissue rather than adding length.
Effects on Muscle and the Brain
IGF-1 wakes up muscle stem cells that repair and enlarge muscle.15PubMed Central. Mechanisms of IGF-1-Mediated Regulation of Skeletal Muscle Hypertrophy and Atrophy They multiply and then fuse into existing fibers. In one experiment, IGF-1 delivered directly into a rat muscle made it about 9% heavier than the untreated leg.16PubMed. Localized infusion of IGF-I results in skeletal muscle hypertrophy in rats About half the effect came from stem cells and half from existing fibers building more protein.17PubMed. Contribution of satellite cells to IGF-I induced hypertrophy of skeletal muscle
In the brain, IGF-1 helps new nerve cells mature, grow branches and form connections, from before birth into adulthood.18PubMed Central. IGF-I: A Key Growth Factor that Regulates Neurogenesis and Synaptogenesis from Embryonic to Adult Stages of the Brain In adults it helps control new nerve cell growth in a memory area of the brain.19PubMed. Mechanisms mediating brain plasticity: IGF1 and adult hippocampal neurogenesis
Most of this comes from animals and cell studies, not people. It helps explain why children with low IGF-1 may have weaker muscles. It does not mean IGF-1 supplements build muscle in healthy adults, and products sold as IGF-1 boosters are not the same as the medicine. Likewise, showing that IGF-1 helps nerve cells branch and connect is not a proven way to improve memory or thinking.
What Happens When the Body Lacks IGF-1
Laron syndrome is a rare condition where the body can’t respond to growth hormone, so it makes little IGF-1.20PubMed Central. Laron Syndrome: A Tale of Two Siblings Babies are born at normal length and weight, but growth slows sharply soon after birth.21PubMed Central. Primary growth hormone insensitivity (Laron syndrome) and acquired hypothyroidism: a case report Untreated adult height ranges from about 116 to 142 cm in men and 108 to 136 cm in women.22PubMed Central. Laron Syndrome: A Tale of Two Siblings Teeth and puberty come late, and features include a prominent forehead, sparse hair, a high voice and low blood sugar.23PubMed Central. Laron Syndrome: A Tale of Two Siblings Body fat rises with age while bones stay thin and muscle is reduced.24PubMed Central. Primary growth hormone insensitivity (Laron syndrome) and acquired hypothyroidism: a case report
People with the condition still reach full sexual development.25PubMed. LESSONS FROM 50 YEARS OF STUDY OF LARON SYNDROME Adults seem protected from cancer but can develop diabetes and heart disease.26PubMed. LESSONS FROM 50 YEARS OF STUDY OF LARON SYNDROME The animal picture is similar: mice lacking IGF-1 reached only 30% of normal adult weight.27PubMed. Role of insulin-like growth factors in embryonic and postnatal growth
Babies start out normal because before birth, growth leans heavily on other signals, including IGF-2 and nutrients from the mother, so it does not depend on growth hormone the way later growth does. After birth, growth hormone and IGF-1 take over as the main drivers, and the shortfall shows up over the first months and years.
In a child, this looks almost the same as ordinary growth hormone deficiency. The difference is that in growth hormone deficiency the hormone is missing, while in Laron syndrome it is present, often high, but ignored. Giving growth hormone helps the first and not the second. A child dropping across growth-chart lines after infancy, delayed teeth or late puberty, or episodes of low blood sugar are reasons to see a pediatrician.
What an IGF-1 Blood Test Shows
Growth hormone levels rise and fall through the day with food and activity.28MedlinePlus. IGF-1 Test: MedlinePlus Medical Test IGF-1 lasts longer in blood and stays more stable,29PubMed. Challenges of insulin-like growth factor-1 testing so one IGF-1 test gives a more reliable view of growth hormone activity.30MedlinePlus. IGF-1 Test: MedlinePlus Medical Test
The test works well for screening children and young adults but less well past age 40.31PubMed. IGF-I measurements in the diagnosis of adult growth hormone deficiency Nutrition and other hormones also change IGF-1.32PubMed. IGF-I measurements in the diagnosis of adult growth hormone deficiency A low level with normal or high growth hormone can mean the body is resisting the hormone.33PubMed. IGF-I measurements in the diagnosis of adult growth hormone deficiency
Normal ranges depend on age and sex. IGF-1 naturally rises through childhood and peaks around puberty, so a number that is normal for a teenager would be high for an older adult. Labs compare a result against a range for the person’s age, and often sex, rather than one cutoff for everyone. A child whose puberty starts late may have a lower level that is still normal for their stage of development.
A low IGF-1 does not by itself prove growth hormone deficiency, because poor nutrition, chronic illness and other conditions can lower it. A low result usually leads to a stimulation test, in which a medicine prompts the pituitary to release growth hormone while blood samples track the response. Doctors combine this with the child’s growth chart and a bone-age X-ray rather than relying on one number. In adults, a high result can prompt checks for a pituitary tumor.
Diet, Fasting and Exercise
Fasting lowered IGF-1 by about 29 ng/mL on average.34PubMed. The influence of fasting and energy restricting diets on IGF-1 levels in humans: A systematic review and meta-analysis Milder diets did not reliably lower it; it took cuts of half or more of daily calories.35PubMed. The influence of fasting and energy restricting diets on IGF-1 levels in humans: A systematic review and meta-analysis The reason is that low insulin during fasting tells the liver to make less IGF-1,36PubMed Central. The Fascinating Interplay between Growth Hormone, Insulin-Like Growth Factor-1, and Insulin which guards against IGF-1 pushing blood sugar too low.37PubMed Central. The Fascinating Interplay between Growth Hormone, Insulin-Like Growth Factor-1, and Insulin In rats, levels bounce back with refeeding, though not fully within a day.38PubMed. Effect of fasting on insulin-like growth factor-I (IGF-I) and growth hormone receptor mRNA levels and IGF-I gene transcription in rat liver
For testing, tell the doctor about any fasting or dieting beforehand. A child who is eating poorly may test low without a hormone problem, and undernutrition can itself slow growth through this pathway. The drops in studies came from fasting or severe calorie cuts, not ordinary dieting, so most adults trying to lose weight needn’t worry about their IGF-1.
Exercise is less clear. Most studies find it doesn’t change total blood IGF-1, though results conflict.39Elsevier. Exercise and the growth hormone–insulin-like growth factor axis Fitter adults tend to have higher IGF-1, linked to endurance rather than strength.40Elsevier. Exercise and the growth hormone–insulin-like growth factor axis
Treatment With Man-Made IGF-1
Mecasermin is genetically engineered human IGF-1.41Australian Prescriber. Mecasermin for primary insulin-like growth factor-1 deficiency It was approved in the US in 2005 and Europe in 2007 for severe IGF-1 deficiency.42PubMed Central. Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency It is injected under the skin twice a day, shortly before or after a meal, to avoid low blood sugar.43Australian Prescriber. Mecasermin for primary insulin-like growth factor-1 deficiency It boosts growth but can increase body fat.44PubMed. LESSONS FROM 50 YEARS OF STUDY OF LARON SYNDROME45PubMed. Mecasermin (recombinant human insulin-like growth factor I)
Growth hormone shots don’t help these children because the problem lies past growth hormone, as in Laron syndrome; giving IGF-1 directly bypasses the broken step. Doctors generally confirm severe deficiency with blood tests, including IGF-1 levels and growth hormone testing, before prescribing it. It is not a growth booster for children who are simply short but have normal levels.
Day to day, skipping a meal after a dose risks shakiness or fainting. Families learn to recognize and treat low blood sugar, and regular growth checks show whether the treatment is working.
Can Too Much IGF-1 Be Harmful
Adults with the highest IGF-1 had about 8% higher overall cancer risk than those with the lowest.46PubMed Central. Circulating Insulin-Like Growth Factor-1 and Risk of Total and 19 Site-specific Cancers: Cohort Study Analyses from the UK Biobank Risks were about 20% to 25% higher for breast, prostate and bowel cancer.47PubMed Central. Circulating Insulin-Like Growth Factor-1 and Risk of Total and 19 Site-specific Cancers: Cohort Study Analyses from the UK Biobank A separate German study found similar links for breast and prostate cancer.48PubMed Central. IGF-1 and Risk of Morbidity and Mortality From Cancer, Cardiovascular Diseases, and All Causes in EPIC-Heidelberg Yet genetically higher IGF-1 was linked to lower bladder cancer risk.49PubMed. Associations of genetically predicted circulating insulin-like growth factor-1 and insulin-like growth factor binding protein-3 with bladder cancer risk A plausible reason for the overall pattern is that IGF-1 helps cells survive and divide, the same actions that drive growth.50PubMed Central. The signaling landscape of insulin-like growth factor 1
An 8% higher relative risk is a small shift from a person’s baseline chance, not an 8-point jump, so most people with higher IGF-1 will not develop cancer. A high IGF-1 result is not a cancer screening test and does not by itself call for cancer testing.
These findings show links, not proof of cause. People with higher IGF-1 may differ in diet, body size, age or health in ways that also affect cancer. Studies that use genetic differences in IGF-1 test cause more fairly, but results vary by cancer type.
On aging, weakening this signaling can more than double lifespan in roundworms,51PubMed Central. Insulin, IGF-1 and longevity and several mouse strains with reduced signaling live longer.52PubMed Central. Insulin, IGF-1 and longevity Animal lifespan results don’t translate directly to people, and high-dose IGF-1 products sold for anti-aging are not recommended.