insulin-like growth factor
Meaning of insulin-like growth factor: Named for its resemblance to insulin, this protein is the reason growth hormone lengthens bone without acting on it directly.
Definition of insulin-like growth factor
Insulin-like growth factor is a pair of small proteins, IGF-1 and IGF-2, that tell cells to enlarge, divide and stay alive. IGF-1 carries out most of the work of growth hormone and is made chiefly by the liver. The name records a structural likeness to insulin, close enough that each of the two can weakly stimulate the other's receptor.
Why is it called insulin-like?
The molecule folds into much the same shape as insulin and shares a good part of its sequence, because both descend from a single ancient protein. The resemblance is more than a curiosity. Each can attach weakly to the other's receptor, so a very high level of one produces a faint version of the other's effect. That is why certain tumors making IGF-2 cause low blood sugar: the excess protein leans on the insulin receptor and pushes glucose into cells. The same overlap is why growth signaling and insulin resistance are studied together.
What keeps it in check?
Almost none of the IGF in blood floats free. A family of binding proteins holds it, stretching its life in the circulation from minutes to hours and keeping it idle until it is released near a target tissue. This carrier system means the total measured in a sample is not the amount available to act. Enzymes that cut the binding proteins are one way a tissue frees up a local supply. The insulin-like growth factor receptor then receives the signal and relays it inside the cell.
What happens when there is too much or too little?
| State | Cause | Result |
|---|---|---|
| Excess in childhood | Too much growth hormone before the growth plates close | Gigantism, unusual height |
| Excess in adulthood | Too much growth hormone after the plates close | Acromegaly, thickened bone and soft tissue |
| Shortage | Growth hormone deficiency, malnutrition or liver disease | Slowed growth in a child, less muscle and bone in an adult |
| Receptor fault | Inherited insensitivity to growth hormone | Short stature with high growth hormone and low IGF-1 |
Does diet change it?
Protein and total energy intake both raise IGF-1, and prolonged fasting lowers it. Milk drinking is associated with higher levels in several studies. Whether nudging the level through diet alters the risk of any disease is unsettled, and the observed associations are small. Because the same signal that repairs tissue also keeps cells alive when they might otherwise die on cue, this protein sits at the center of a long running argument about growth, aging and cancer risk that no single study has resolved. Blood levels are interpreted against age, since the normal range shifts across a lifetime.
Also known as
Used in a sentence
Insulin-like growth factor 1 was elevated, supporting the diagnosis of acromegaly.
Good to know
Most insulin-like growth factor in blood is bound to carrier proteins rather than free, so the total measured in a sample exceeds the amount able to act, and the normal range shifts with age.