IGF-1Insulin-like growth factor 1 · Somatomedin C
A growth factor that mediates many of growth hormone's effects on tissue.
IGF-1, insulin-like growth factor 1, is produced mainly by the liver in response to growth hormone and locally within muscle in response to loading. Structurally similar to insulin, it promotes cell growth and division and suppresses programmed cell death.
It matters clinically because it is stable in the blood, unlike growth hormone, which is released in pulses and nearly uninterpretable from a single sample. IGF-1 is therefore what clinicians measure to assess growth hormone status.
In muscle, the locally produced version responds to mechanical loading and contributes to the repair and growth that follow, which is one of the ways training and hormonal signalling intersect.
It sits at an unresolved tension in ageing research. Higher IGF-1 supports muscle and bone, while lower lifetime IGF-1 signalling is associated with longer life in several animal models and in some human populations with growth hormone receptor deficiency. Growth and longevity appear to pull against each other, and nobody has established where the optimum sits for a person.
That tension is a good reason to be sceptical of anything marketed as an IGF-1 booster, both because the products rarely do anything measurable and because it is not obvious that more would be better if they did.
Deer antler velvet is the clearest example of the marketing failure. It is sold on its IGF-1 content, which is a protein that would be digested if swallowed, is present in tiny amounts, and is prohibited in sport, making the products an anti-doping risk without a mechanism.
In practice, treat IGF-1 as a measurement clinicians use rather than a target to raise, and take an abnormal result to a doctor.