Growth Factors in Colostrum: What Are IGF-1 and IGF-2?

Colostrum contains growth factors that signal your body to repair tissue, build muscle, and restore resilience. But the quantities matter, and so does understanding how they actually work.

This is where colostrum marketing often diverges from the biology. Growth factors matter, but not in the way most people imagine.

What IGF-1 and IGF-2 are

IGF-1 (insulin-like growth factor 1) and IGF-2 (insulin-like growth factor 2) are peptide hormones produced throughout your body, but most abundantly by the liver in response to growth hormone signalling. They are called insulin-like because their structure resembles insulin, but their functions are distinct.

IGF-1 is the primary growth factor. It signals cells to grow, divide, and resist apoptosis (cell death).¹ It is essential for childhood growth, muscle development, bone strength, and throughout life for tissue repair and metabolic function. Low IGF-1 is associated with rapid ageing, weak muscles, poor recovery, and increased mortality risk.

IGF-2 is a fetal growth factor, more abundant during development and less active in adults. It plays a role in fetal growth, some aspects of tissue repair, and metabolic regulation, but is less well studied than IGF-1.

Both are produced by your body endogenously (internally). The question colostrum raises is whether consuming additional IGF from external sources (bovine colostrum) provides benefit, or whether it simply gets digested and broken down like any other protein.

IGF-1 and IGF-2 are growth signals your body produces. Colostrum contains them. But consumption does not mean absorption, and absorption does not mean function.

The role of growth factors in tissue repair

After training or injury, your body must repair damaged tissue. This requires signals (growth factors) and raw materials (amino acids, minerals, cofactors). Growth factors orchestrate the repair process.

When you train hard, muscle fibres are damaged. IGF-1 signals muscle satellite cells to activate, proliferate, and differentiate into new muscle cells. Growth hormone and testosterone support this process. The amino acids you eat provide the material for protein synthesis. The result is muscle repair and growth.

When your gut is damaged (from illness, antibiotics, or exercise-induced permeability), growth factors signal intestinal epithelial cells to repair the damage. IGF-1 directly promotes cell division and protein synthesis in intestinal tissue. It also promotes the production of mucins (the protective mucus layer lining your gut).

This is why growth factors matter. They are not just present in colostrum for show. They actively facilitate tissue repair. If you are training hard or recovering from illness or gut damage, adequate growth factor status supports faster, more complete recovery.

The challenge is delivering growth factors in useful form. Most dietary proteins (including growth factors) are broken down into amino acids during digestion. The intact growth factor molecules are typically too large to cross the intestinal barrier and enter the bloodstream.

Physiological vs supraphysiological levels

This is where the confusion sets in. Colostrum marketing claims that the IGF-1 in colostrum is absorbed and has physiological effects. This is partly true but requires nuance.

Your body maintains a tightly regulated blood level of IGF-1. In healthy adults, this level sits around 100 to 300 ng/ml, depending on age, sex, and growth hormone status. This is the physiological level that supports normal tissue repair and metabolic function.

Colostrum contains roughly 2 to 5 micrograms of IGF-1 per gram of colostrum (quality varies).² A 25-gram serving contains 50 to 125 micrograms of IGF-1. Even if all of this were absorbed intact (which it is not), it would be a negligible amount compared to your body's endogenous production, which is roughly 10 to 40 micrograms per kilogram of body weight daily. For a 70-kilogram person, that is 700 to 2,800 micrograms daily from internal sources alone.

So the colostrum-derived IGF-1 is not achieving supraphysiological levels (high enough to cause the exaggerated effects sometimes promised). It is providing a small amount of dietary IGF-1 that may contribute to physiological needs but is not a breakthrough on its own.³

However, the mechanism of action might not be direct. Rather than intact IGF-1 being absorbed and exerting effects, the amino acids from colostrum (particularly the branched-chain amino acids) may stimulate your own endogenous IGF-1 production. Additionally, the growth hormone in colostrum may stimulate your liver's IGF-1 production.

Colostrum does not contain enough IGF-1 to raise your blood levels substantially. But it may stimulate your body to produce more of its own, which is arguably more useful.

How much IGF is actually in colostrum

Quality bovine colostrum contains roughly 2 to 5 micrograms of IGF-1 per gram, and 5 to 10 micrograms of IGF-2 per gram.² These are not large quantities.

The highest-quality, freeze-dried colostrum powders contain the highest IGF concentrations. Powders that have been heated or processed extensively (pasteurised at high temperature) have reduced growth factor content because growth factors are sensitive to heat. Liquid colostrum from the supermarket is likely to be significantly lower in growth factors than quality powdered colostrum.

Source matters. Colostrum from grass-fed cattle appears to have higher growth factor content than colostrum from grain-fed cattle, though the evidence is not definitive. Colostrum collected in the first 6 to 12 hours post-delivery is richer in growth factors than colostrum collected later in the lactation cycle (when growth factor concentrations decline).

The practical point: if you are choosing colostrum specifically for growth factor content, quality matters immensely. You could be taking 5 times more or 5 times less IGF depending on sourcing and processing.