IGF
Meaning of IGF: The messenger through which growth hormone does its work, since most of what growth hormone achieves is carried out by IGF-1.
Definition of IGF
IGF stands for insulin-like growth factor, a family of small proteins that push cells to enlarge, divide and stay alive. The liver releases most of the circulating supply after growth hormone signals it to. Two members are recognized, IGF-1 and IGF-2, and the name records a chemical likeness to insulin close enough that each can weakly trigger the other's receptor.
How does IGF relate to growth hormone?
The pituitary gland releases growth hormone in pulses, mostly during sleep. Growth hormone acts on the liver, and the liver responds by making IGF-1 and releasing it into the blood. Most of the growth that follows is the work of IGF-1 rather than of growth hormone itself. Because the growth hormone level swings from hour to hour while IGF-1 stays comparatively steady, a single IGF-1 measurement reflects long term output far better. IGF-1 also feeds back to the pituitary and damps further release.
What separates IGF-1 from IGF-2?
| IGF-1 | IGF-2 | |
|---|---|---|
| Main period of action | Childhood growth and adult tissue upkeep | Growth before birth |
| Controlled by | Growth hormone and nutrition | Largely independent of growth hormone |
| Why the level is measured | To assess growth hormone excess or shortage | Occasionally raised by rare tumors that cause low blood sugar |
Why does the level rise or fall?
Nutrition is the strongest everyday influence. Starvation and severe illness push IGF-1 down even when growth hormone is high, which is one reason growth stalls in a malnourished child. Levels run high through the teenage years and decline steadily with age. Disease shifts them as well. In acromegaly a pituitary tumor drives growth hormone and IGF-1 up together, thickening bone and soft tissue in an adult. Liver disease lowers IGF-1 because the liver is the factory. As a growth factor, IGF-1 also keeps alive cells that would otherwise die on schedule.
Is there a link with cancer?
Signals telling cells to grow and resist death are exactly the signals a tumor profits from, so the question has been studied hard. Population studies report modest associations between higher IGF-1 in blood and later diagnosis of some cancers, but associations of that size do not establish cause, and drugs blocking the IGF-1 receptor have so far disappointed in trials. What is settled is that IGF resembles insulin closely enough to overlap with it, tying growth signaling to the way the body handles sugar.
Also known as
Used in a sentence
Serum IGF-1 was measured as part of the workup for suspected growth hormone excess.
Good to know
A single IGF-1 level reflects growth hormone output over days rather than at the instant of the draw, but it also falls with poor nutrition, liver disease and advancing age, so a low result does not by itself indicate a pituitary problem.