IGF-1: Low vs High Signs, Testing, Recovery, and Healthy Aging
Overview
IGF-1, or insulin like growth factor 1, is a hormone mainly produced by the liver in response to growth hormone. It acts as a longer term signal for tissue repair, muscle and bone building, and body composition, and tends to be much more stable across the day than growth hormone itself. Clinicians often use IGF-1 as a key marker when they are evaluating suspected growth hormone deficiency or excess, tracking recovery, or thinking about longer term healthy aging.
In practice, IGF-1 is usually interpreted together with Growth Hormone so that both the short term pituitary signal and the longer term tissue level effect can be seen side by side.
What IGF-1 is and where it is made
IGF-1 is a peptide hormone that is structurally similar to insulin and is part of the growth hormone axis.
It is produced mainly by the liver when growth hormone stimulates liver cells, but many tissues can make smaller local amounts.
IGF-1 circulates in the bloodstream bound to carrier proteins, which help keep levels relatively stable across the day.
What IGF-1 does in your body
Supports linear growth in children and adolescents by acting on bone, cartilage, and growth plates.
Helps maintain muscle mass and strength and supports tissue repair after exercise or injury.
Contributes to bone density and skeletal integrity across adulthood.
Influences body composition by supporting lean mass and helping regulate fat storage and breakdown.
Affects metabolic health, including how the body handles glucose and lipids, especially when levels are very high or very low.
Participates in healthy aging pathways when kept in a balanced range for age and context.
When testing IGF-1 makes sense
Evaluation of short stature or growth delay in children when growth hormone related causes are being considered.
Suspected growth hormone deficiency in adults with reduced muscle mass, low exercise capacity, increased fat mass, or low bone density.
Suspected growth hormone excess, such as acromegaly, when there are changes in facial features, hand or foot size, sweating, or joint symptoms.
Assessment of pituitary function when other pituitary hormones or imaging suggest a problem.
Monitoring of prescribed growth hormone therapy to see whether the dose is in a suitable range over time.
How to think about high and low IGF-1 results
This information is general and does not replace lab specific reference ranges or medical evaluation.
Low IGF-1 might be associated with:
Reduced growth rate in children compared with peers and expected family height.
In adults, lower muscle mass, reduced strength or exercise capacity, and higher fat mass.
Low bone density or increased fracture risk, especially with other risk factors.
Possible contributors include growth hormone deficiency from pituitary or hypothalamic disease, prior pituitary surgery or radiation, severe undernutrition, chronic illness, or advanced liver disease. Interpretation usually requires specialist input and more than one test.
High IGF-1 might be associated with:
Growth hormone excess, including acromegaly in adults or excessive growth in children.
Symptoms such as enlargement of hands and feet, changes in facial features or jaw size, joint pain, headaches, or sweating.
Increased risk of some metabolic issues and, in some cases, higher risk of certain complications if not treated.
High IGF-1 is most often related to growth hormone secreting pituitary tumors and needs careful endocrine evaluation. Borderline or unexpected results often need confirmation and repeat testing before any conclusions are drawn.
What can influence your IGF-1 levels
Growth hormone secretion patterns, which are driven by sleep, exercise, stress, and pituitary health.
Age, since IGF-1 is higher during adolescence and naturally declines through adulthood.
Nutrition status, including overall calorie intake, protein intake, and chronic undernutrition.
Chronic illness, inflammation, and liver disease, which can reduce IGF-1 production.
Obesity, insulin resistance, and metabolic state, which can alter the growth hormone IGF-1 axis.
Growth hormone therapy or other treatments that interact with this hormonal pathway.
Rare genetic conditions that affect growth hormone receptors or IGF-1 production.
When to talk to a clinician
Concerns that a child is significantly shorter or growing more slowly than expected for age and family height.
Adult symptoms that suggest growth hormone deficiency or excess, such as major changes in body composition or enlargement of hands, feet, or facial features.
Known pituitary disease or prior brain or pituitary treatment with new symptoms like headaches, vision changes, or fatigue.
Questions about whether growth hormone or related therapies are appropriate, safe, or correctly dosed.
An endocrinologist can decide which tests to use, including IGF-1 and possible stimulation or suppression tests, and interpret results in context with imaging and other hormones.
IGF-1 in one view
IGF-1 is the more stable, longer term reflection of growth hormone activity that helps shape growth, muscle, bone, and body composition across life. On its own it is a signal, not a diagnosis, and becomes most useful when interpreted with growth hormone, symptoms, and imaging, often alongside structured training and recovery habits such as a Zone 2 Endurance plan. If your IGF-1 result is outside range or does not match what is happening in your body, it is a reason to speak with an endocrinologist rather than to self adjust hormones or supplements.
