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

This is where colostrum marketing often diverges from the biology. Growth factors are powerful, 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 game-changer 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.

Bioavailability and absorption

IGF-1 is a peptide hormone. It is not stable in your stomach's acidic environment, and it is too large to cross the intestinal barrier intact.³ Most dietary IGF-1 is broken down into constituent amino acids during digestion.

This means that the IGF-1 you consume in colostrum is likely not being absorbed as intact IGF-1 and circulated in your bloodstream. Instead, it is being hydrolysed into amino acids and dipeptides. Some small amount might be absorbed intact if there is intestinal permeability, but this is not the primary mechanism.

What is useful is the amino acid profile. IGF-1 is made from amino acids, and the amino acids from digested IGF-1 can be used by your body to synthesise its own IGF-1 or other proteins. Additionally, the branched-chain amino acids (particularly leucine) from colostrum stimulate muscle protein synthesis and may trigger your own growth hormone and IGF-1 production.

So the practical benefit of colostrum's growth factors is not that you absorb intact growth factors. It is that colostrum provides amino acids and compounds that stimulate your body to produce and utilise its own growth factors more effectively.

This is less romantic than the idea that you are absorbing pre-made growth factors, but it is also more realistic and actually more useful. You cannot rely on external sources of growth factors, but you can support your body's own capacity to produce them.

Practical implications for recovery

Understanding growth factor bioavailability changes how you use colostrum effectively.

Colostrum's value for recovery is not primarily because it delivers intact growth factors. It is because it provides a concentrated source of amino acids, immunoglobulins, lactoferrin, and other compounds that support immune function, gut integrity, and tissue repair.

The growth factors themselves are less important than the amino acid profile. A 25-gram serving of quality colostrum provides 7 to 10 grams of protein, including substantial branched-chain amino acids (roughly 1 to 2 grams of leucine). These amino acids directly stimulate muscle protein synthesis and trigger endogenous growth factor production.

If your goal is to maximise recovery, take colostrum immediately post-training (within 30 to 60 minutes), in the window when your muscles are most responsive to growth signals and amino acids. Combine it with vitamin C (which supports growth factor signalling) and adequate carbohydrates (which promote anabolic hormonal status).

The combination of colostrum's amino acids, immunoglobulins, and immune-supporting compounds, taken during this window, supports recovery more effectively than any single component alone.

Additionally, consistent colostrum supplementation during heavy training blocks (20 to 30 grams daily) maintains immune function and gut integrity, allowing your body's own growth factor production to proceed unimpeded by infection or intestinal inflammation. This is arguably more valuable than the growth factors in colostrum itself.

Growth factors in colostrum are present and potentially useful, but their value is subtle. They support tissue repair and adaptation, but not through dramatic mechanisms. Expect modest benefits, not transformation. Taken consistently as part of a broader recovery strategy (adequate sleep, training stimulus, nutrient density, stress management), colostrum is an effective tool. Expected as a standalone recovery solution, it disappoints.

References

1. 1. Laron Z. Insulin-like growth factor 1 (IGF-1): a growth hormone. Mol Pathol. 2001;54(5):311-316. PMC1187088
2. 2. Arslan A, et al. Revealing the Potency of Growth Factors in Bovine Colostrum. Animals. 2024. PMC11279796
3. 3. Kuhne S, et al. Oral bovine colostrum supplementation does not increase circulating insulin-like growth factor-1 concentration in healthy adults. Eur J Clin Nutr. 2019. PMID 31123862