What is the IGF factor in milk? A Comprehensive Guide to IGF-1

October 20, 2025 •

4 min read

Naturally present in all milk, including cow's and human milk, the IGF factor plays an essential role in the growth and development of the newborn gastrointestinal tract. However, its presence has also sparked debates and questions regarding its effects on adults.

Quick Summary

This guide explains the function of insulin-like growth factors (IGFs) in milk, comparing levels in human and cow milk. It details how dairy processing affects IGF-1 and clarifies current scientific understanding regarding its safety and bioavailability for adults.

Key Points

Natural Presence: The IGF factor, mainly IGF-I, is a naturally occurring polypeptide hormone in the milk of all mammals, including humans and cows.
Role in Infants: Milk-borne IGF-I plays a beneficial role in promoting the growth and maturation of the gastrointestinal tract in newborns.
Minimal Absorption: In adults, IGF-I is a protein that is largely digested by the body. The amount absorbed intact into the bloodstream is considered minimal and biologically insignificant.
Endogenous vs. Dietary Intake: The body's own production of IGF-I far exceeds any amount that could be absorbed from drinking milk, making the dietary contribution inconsequential.
Processing Matters: While pasteurization does not significantly alter IGF-I levels, high-heat sterilization and fermentation can destroy or reduce its content.
No Proven Cancer Link: Despite public concern, major scientific and regulatory bodies have found no evidence that consuming IGF-I from milk increases cancer risk.

What are Insulin-like Growth Factors (IGFs)?

IGF stands for Insulin-like Growth Factor, and the primary one found in milk is IGF-I. It is a polypeptide hormone that is structurally similar to insulin. IGF-I plays a vital role in regulating cell growth, metabolism, and proliferation across many bodily tissues. In milk, IGFs serve a crucial purpose, particularly for the newborn consuming it. These growth factors assist in the healthy development of the gastrointestinal tract, promoting cell differentiation and growth. The concentration of IGF-I is typically highest in colostrum, the milk produced immediately after birth, and decreases as lactation progresses.

IGF in Bovine Milk vs. Human Milk

It is a common misconception that IGF-I is exclusive to cow's milk. In fact, IGF-I is found in the milk of all mammals, including humans. A key distinction, however, lies in their relative concentrations and species-specific properties. Interestingly, studies have shown that human breast milk contains naturally higher concentrations of IGF-I compared to bovine milk. Despite this, the IGF-I molecule is structurally identical in bovines and humans, meaning that if it were to be absorbed intact, the human body would recognize and utilize it.

Factors that influence IGF-I concentration in milk include:

Stage of lactation: Levels are highest in the initial colostrum and decline over time.
Cow's diet: The nutritional intake of the cow affects the hormone levels.
Genetics: Individual genetic variations influence IGF-I production.
Use of rBGH: Cows treated with recombinant bovine growth hormone (rBGH) produce higher concentrations of IGF-I in their milk, though these levels remain within the normal physiological range of natural milk.

Effects of Milk Processing on IGF-I Levels

Dairy processing can impact the level and bioactivity of IGF-I in the final product. Understanding these effects helps clarify the safety concerns often raised by consumers.

Pasteurization: Normal pasteurization conditions (e.g., 79°C for 45 seconds) do not significantly alter IGF-I concentrations. This means pasteurized milk contains similar levels of IGF-I as raw milk.
Fermentation: The fermentation process, used for products like yogurt, can significantly reduce IGF-I content. Lactic acid bacteria present during fermentation can utilize IGF-I as a nutrient source, leading to a considerable decrease in its concentration.
High-Heat Sterilization: Intense heat treatments, such as autoclaving at 121°C for five minutes, can denature and completely eliminate detectable levels of IGF-I. This is relevant for products like infant formula, where high-temperature processing is standard.
Homogenization: This process, which breaks down fat globules, has little to no effect on IGF-I concentration.

Health Concerns and Scientific Consensus

For years, there has been public debate over whether consuming milk-borne IGF-I could increase cancer risk by elevating circulating IGF-I levels in humans. The scientific consensus from major regulatory bodies provides important clarity on this issue.

Bioavailability of Dietary IGF-I

For orally consumed IGF-I to have an effect on the human body, it must survive digestion and be absorbed intact into the bloodstream. The gastrointestinal tract is highly efficient at digesting proteins, and IGF-I is rapidly degraded in the gut. The amount of intact, orally-absorbed IGF-I entering the systemic circulation is considered minimal, particularly in adults. The body's own natural production of IGF-I is millions of times higher than the amount consumed from milk, making the dietary contribution negligible.

IGF-I and Cancer Risk

While some epidemiological studies have noted an association between higher circulating IGF-I levels and an increased risk of certain cancers, they have failed to establish a causal link with milk consumption. Regulatory bodies like the US Food and Drug Administration (FDA) and the UK Committee on Carcinogenicity (COC) have concluded that the evidence does not show that IGF-I from food increases cancer risk. In fact, some studies even suggest a protective effect of milk and dairy against certain cancers like colorectal cancer, particularly in high-risk individuals.

The Role of Milk Protein

Some research suggests that dietary milk protein, rather than the IGF-I itself, might be responsible for observed increases in systemic IGF-I levels after milk consumption. This is an area of ongoing research, but it further differentiates the cause from the intact IGF-I molecule found in milk.

Comparison of IGF-I Sources and Bioavailability


Feature	Bovine Milk	Human Milk	Adult Endogenous Production	Dietary Bioavailability	Heat Stability	Cancer Risk
Source	Produced in cow's mammary gland	Produced in human mammary gland	Produced primarily by the liver	External intake via food	Varies by temperature	Associated with high systemic levels
Concentration	Variable, influenced by lactation and diet; generally lower than human milk	Variable, generally higher than bovine milk	Very high, in milligram range	Minimal amount absorbed intact	Normal pasteurization: stable; Sterilization: destroyed	Dietary IGF-I is not proven to increase risk
Effect on Body	Promotes calf gut and tissue development	Promotes infant gut and tissue development	Controls systemic growth and metabolism	Not believed to have a significant effect on adult systemic levels	N/A	High systemic levels are a potential risk factor; not caused by dietary intake

Conclusion

The IGF factor in milk, primarily IGF-I, is a naturally occurring polypeptide hormone essential for the development of newborns. While its presence in milk, particularly bovine milk, has raised public concerns regarding human health, a substantial body of scientific evidence indicates that these fears are largely unfounded. Due to rapid digestion, the absorption of intact IGF-I from dietary sources in adults is minimal, and the amount is dwarfed by the body's own production. Scientific and regulatory bodies agree that dietary IGF-I does not pose an increased cancer risk to consumers. The potential link between dairy consumption and systemic IGF-I appears to be more related to milk proteins than the IGF-I itself, and this area continues to be studied. Ultimately, milk remains a nutrient-rich food source, and the science suggests that the IGF factor within it does not represent a significant health risk for the vast majority of consumers. For more detailed information on IGF-I and cancer risks, consult authoritative sources like the UK's Committee on Carcinogenicity non-technical summary.

Frequently Asked Questions

The IGF factor in milk refers to Insulin-like Growth Factor I (IGF-I), a hormone-like protein that naturally occurs in the milk of all mammals. It promotes cell growth and is essential for the healthy development of the newborn gastrointestinal tract.

Yes, milk from cows treated with recombinant bovine growth hormone (rBGH) may contain slightly higher levels of IGF-I than milk from untreated cows. However, these levels typically remain within the normal physiological range seen in untreated cows, and any difference is not considered a significant health risk.

Yes, bovine IGF-I and human IGF-I are structurally identical molecules. This is one reason for the debate around its potential effects, though most dietary IGF-I is not absorbed intact.

No, major health bodies have concluded there is no convincing evidence that IGF-I from milk increases cancer risk. Dietary IGF-I is mostly digested and the amount absorbed is negligible compared to what the human body produces naturally.

Standard pasteurization has little effect on IGF-I levels. However, higher heat treatments used for sterilization or fermentation (like for yogurt) can significantly reduce or eliminate the IGF-I content.

Human breast milk naturally contains a higher concentration of IGF-I than cow's milk.

For infants, milk-borne IGF-I is beneficial for gut development. For adults, evidence suggests milk consumption promotes growth via systemic IGF-I increases, though this may be a secondary effect of milk proteins rather than direct absorption of IGF-I itself.