Insulin-Like Growth Factor (IGF)
Written by SiPhox Health Research Team
Last updated: September 24, 2026
4 mins read
What is IGF-1?
Insulin-like growth factor 1 (IGF-1) is a hormone that plays an important role in growth, tissue repair, muscle and bone health, and metabolism. IGF-1 is produced primarily by the liver in response to growth hormone (GH) and is responsible for many of GHโs effects throughout the body.
Unlike growth hormone, which is released in pulses and can fluctuate substantially throughout the day, IGF-1 remains relatively stable. This makes it a useful marker for assessing activity of the growth hormone and IGF-1 system.
IGF-1 is unusual because higher is not necessarily better. Levels naturally decline throughout adulthood, so a healthy IGF-1 level for someone in their 20s can look very different from a healthy level for someone in their 60s or 70s.
Why is IGF-1 important?
IGF-1 to provides insight into your growth hormone and metabolic health. IGF-1 helps support the maintenance of muscle, bone, and other tissues throughout adulthood.
IGF-1 is also commonly used by healthcare providers when evaluating growth hormone disorders because it provides a more stable reflection of growth hormone activity than a single GH measurement. Both unusually low and unusually high IGF-1 levels can sometimes indicate changes in the growth hormone system, although an IGF-1 result alone cannot diagnose a growth hormone disorder.
How can I better understand my IGF-1 levels?
Unlike biomarkers with one standard adult cutoff, IGF-1 should be interpreted according to your age. IGF-1 rises through childhood and adolescence, peaks around puberty and young adulthood, and then gradually declines with age. Large reference studies involving thousands of healthy people demonstrate this strong age-related pattern.
Sex can also affect IGF-1 reference values depending on age and the laboratory method used. SiPhox therefore compares your result with the age- and sex-specific reference range that applies to you.
These values match the current Labcorp IDS-iSYS IGF-1 reference intervals. Labcorp established these age- and sex-adjusted intervals using a very large U.S. clinical population and notes that IGF-1 reference intervals are assay-specific.
IGF-1 should therefore not be interpreted against one universal โidealโ concentration. Instead, SiPhox evaluates your result relative to the expected range for your age and sex.
Population studies also suggest that being at either extreme of the IGF-1 distribution may be less favorable than being closer to the middle. A meta-analysis of nearly 15,000 adults found a U-shaped relationship between IGF-1 and mortality, with both approximately the lowest 10% and highest 10% of age-related IGF-1 levels associated with higher mortality than values around the middle of the distribution. A later meta-analysis involving more than 30,000 adults similarly found higher mortality at both low and high IGF-1 concentrations.
How can I maintain optimal IGF-1 levels?
Because IGF-1 naturally changes with age, the goal is not to make IGF-1 as high as possible. Instead, focus on supporting normal growth hormone and metabolic function.
Nutrition: Adequate nutrition is important for maintaining normal IGF-1 production. Undernutrition and significant calorie or protein restriction can lower IGF-1, even when growth hormone production is normal.
Exercise: Regular physical activity supports muscle, bone, and metabolic health and interacts with the growth hormone and IGF-1 system. Exercise can affect circulating IGF-1, although the response varies according to age, health status, and exercise type.
Sleep: Growth hormone secretion is strongly linked to sleep, particularly deep sleep. Maintaining consistent, adequate sleep helps support normal regulation of the growth hormone and IGF-1 system.
Consider the bigger picture: Nutrition, body composition, liver function, metabolic health, pregnancy, and certain medications can all affect IGF-1 levels. Current endocrine consensus recommends interpreting IGF-1 in the context of these factors rather than relying on the number alone.
If your IGF-1 is persistently outside your age-specific laboratory range, discuss the result with your healthcare provider. Repeat testing or additional evaluation may be appropriate depending on your result, symptoms, and medical history.