Is Raw Milk High in IGF-1?

December 25, 2025 •

5 min read

Studies have shown that raw milk naturally contains insulin-like growth factor 1 (IGF-1), a hormone that is structurally identical in humans and bovines. The level of IGF-1 in milk, including raw milk, can be influenced by various factors, leading to fluctuating concentrations.

Quick Summary

Raw milk contains IGF-1, though levels vary based on factors like cow breed and lactation stage. Studies show pasteurization and fermentation can affect IGF-1 content. The human absorption of intact bovine IGF-1 is also a complex and debated topic.

Key Points

Presence in Milk: Raw milk naturally contains insulin-like growth factor 1 (IGF-1), a growth-promoting hormone essential for mammalian development.
Effect of Processing: Pasteurization and other heat treatments significantly reduce or eliminate the presence of active IGF-1 in milk, meaning raw milk retains more of its native IGF-1 content.
Natural Variation: IGF-1 levels in raw milk are highly variable and depend on factors such as the cow's breed, stage of lactation, diet, and whether it has been treated with hormones like rBGH.
Human Absorption: The absorption and biological activity of orally ingested bovine IGF-1 in humans is a debated topic, with some regulatory bodies suggesting it is unlikely to be absorbed in significant, intact quantities.
Indirect Systemic Impact: Consumption of dairy products, both raw and pasteurized, can indirectly increase systemic IGF-1 levels in humans by providing high-quality protein and amino acids that stimulate the body's own production.
Health Debates: High systemic IGF-1 levels have been associated with both beneficial effects (growth) and potential risks (certain cancers), though the direct link between milk consumption and cancer remains inconclusive.

Understanding IGF-1 in Dairy

Insulin-like growth factor 1 (IGF-1) is a polypeptide hormone that plays a crucial role in cell growth, metabolism, and development. It is naturally present in all mammalian milk, including bovine and human, as it is essential for the growth of newborns. The concentration of IGF-1 in raw milk is not static; it fluctuates significantly due to a variety of factors related to the cow and milk processing. For example, a cow's breed, the stage of lactation, and whether it has been treated with recombinant bovine growth hormone (rBGH) can all influence the final IGF-1 concentration. Some research suggests that milk from cows not treated with rBGH contains levels of IGF-1 well within the normal physiological range. A positive correlation has also been observed between IGF-1 concentration and the fat content of milk.

Raw vs. Pasteurized Milk: A Comparative Look at IGF-1

The most significant difference between raw and processed milk in terms of IGF-1 content is the effect of heat treatment. High-temperature processing, such as ultra-high-temperature (UHT) treatment, has been shown to reduce or even eliminate detectable IGF-1 levels in milk. A 2006 study on dairy processes and IGF-1 concentrations found that the IGF-I content in raw milk was significantly altered by the strength of heat treatments. While pasteurization at standard temperatures may have less of an impact, some studies indicate it can slightly lower IGF-1 content, and fermentation for products like yogurt can also cause a significant reduction. Conversely, raw milk, by definition, has not been subjected to these heat treatments, preserving its natural IGF-1 content. This preservation, however, does not mean the IGF-1 is consistently at a high level. Natural variation across different animals and batches remains a dominant factor.

The Impact of Other Dairy Processes

Beyond simple pasteurization, other common dairy manufacturing processes can affect the final concentration of IGF-1 in products. Fermentation, for instance, significantly reduces the IGF-1 content as lactic strains appear to utilize the growth factor. This means that while raw yogurt would likely contain higher IGF-1 than a pasteurized version, the overall content would be lower than in the raw milk it was made from. Likewise, the creation of dried milk powder has been shown to result in no significant change to the IGF-1 concentration, while the content in yogurt decreases significantly during storage.

The Absorption of Bovine IGF-1 in Humans

One of the most debated aspects of IGF-1 in milk is its biological activity in humans. Some studies and reviews have questioned whether orally ingested IGF-1 is absorbed intact through the human gastrointestinal tract in significant amounts. The FDA concluded in 2009 that biologically significant levels of intact IGF-1 from milk would likely not be absorbed and therefore presented no increased health risk to consumers. This is because the digestive system, designed to break down proteins, may inactivate the hormone before it can be absorbed. However, other research highlights that bovine IGF-1 is structurally identical to human IGF-1, which could theoretically allow it to bind to human IGF-1 receptors and elicit a biological effect. Some animal studies have also suggested possible absorption of orally administered IGF-1. The debate continues with conflicting findings in research, emphasizing the need for more conclusive studies on human absorption.

Factors Influencing IGF-1 Levels in Milk

Several factors contribute to the natural variability of IGF-1 in both raw and processed milk. A study on dairy in Mexico found significant differences in the mean IGF-1 concentration between different brands and types of milk, noting a positive correlation between fat content and IGF-1 levels.

Lactation Stage: The stage of lactation has a pronounced effect on IGF-1 concentrations, with the highest levels often found in colostrum and decreasing significantly thereafter.
Cow Breed: Research has identified breed-specific variations in IGF-1 levels, noting, for example, high levels in Holstein cows and lower levels in others.
rBGH Treatment: Cows treated with recombinant bovine growth hormone (rBGH) can have higher mean IGF-1 levels in their milk compared to non-treated cows, although these levels generally remain within the physiological range of naturally occurring IGF-1.
Milk Fat Content: A positive correlation has been established between higher milk fat content and increased IGF-1 concentration.

Comparison Table: Raw Milk vs. Pasteurized Milk IGF-1


Feature	Raw Milk	Pasteurized Milk
IGF-1 Concentration	Naturally present, levels vary widely based on cow factors.	Typically lower than raw milk, with concentration dependent on heat treatment intensity.
Effect of Processing	Unprocessed; retains naturally occurring IGF-1 and other growth factors.	Heat treatment, especially UHT, can significantly degrade or eliminate IGF-1 content.
Absorption by Humans	Theoretical potential for higher intake of active bovine IGF-1, though human absorption remains debated.	Lower potential for intact IGF-1 intake due to heat degradation during processing.
Factors Affecting Levels	Cow's genetics, diet, lactation cycle, and health.	Primarily the heat and processing methods used, but original raw milk levels also factor in.
Safety Concerns	Contains naturally occurring bacteria, including pathogens, and is subject to health warnings.	Safer regarding bacteria due to heat-killing pathogens; health concerns often focused on the consumption of dairy products.

The Health Implications of Milk and IGF-1

Consuming milk, whether raw or pasteurized, has been shown to increase systemic IGF-1 levels in humans, particularly in children. This effect is linked to milk's high amino acid content, especially whey proteins rich in leucine, which triggers insulin production and subsequent IGF-1 synthesis in the body. The IGF-1 contained within the milk itself, though potentially degraded during digestion, might also contribute to this effect, especially since some studies suggest bovine IGF-1 is bio-available. High systemic IGF-1 levels have been associated with both beneficial effects (such as improved growth and muscle repair) and potential risks (increased risk of certain cancers, like prostate and breast cancer). However, the link between dietary IGF-1 from milk and these cancer risks is still debated and inconclusive.

Conclusion

Raw milk does naturally contain insulin-like growth factor 1 (IGF-1), and its concentration can vary widely based on numerous factors related to the animal. Since raw milk is not subjected to heat treatments like pasteurization, it retains a higher concentration of the native IGF-1 compared to commercially processed milk, where high heat can significantly degrade the hormone. The crucial takeaway for consumers is that while raw milk contains more native IGF-1, the ultimate impact on human health depends heavily on the extent to which bovine IGF-1 is absorbed and how the milk's amino acids stimulate the body's own production. Current evidence remains divided on the significance of consuming bovine IGF-1 directly versus the overall dietary impact of dairy protein on systemic IGF-1 levels, emphasizing the importance of informed personal decisions and further research.

Frequently Asked Questions

The potential danger of IGF-1 in milk is a subject of ongoing debate. While high systemic IGF-1 levels in humans have been linked to certain health conditions, the scientific and regulatory consensus is that dietary IGF-1 from milk is unlikely to be absorbed in significant, biologically active amounts by the human digestive system, especially from pasteurized milk.

Yes, pasteurization affects IGF-1 levels. Research indicates that heat treatment, particularly high-temperature pasteurization (UHT), can cause a significant reduction or complete degradation of IGF-1 in milk.

Raw milk contains more IGF-1 because it has not been subjected to the heat treatment process of pasteurization. This process, designed to kill pathogens, also degrades some of the naturally occurring proteins and hormones, including IGF-1.

The amount of IGF-1 in raw milk varies widely, with research showing concentrations ranging from 1 to 83 ng/mL in samples of natural milk. This variability depends on factors like the cow's breed and lactation cycle.

Some studies suggest that consuming milk, including raw, can increase a person's systemic IGF-1 levels. This is largely attributed to the milk's rich protein and amino acid content, which stimulates your body's own production of the hormone, rather than significant absorption of the IGF-1 directly from the milk.

Research has presented conflicting findings regarding a definitive link between milk consumption, IGF-1, and cancer. While some observational studies have found an association between higher systemic IGF-1 and certain cancer risks, a direct causal link from dietary milk IGF-1 is not strongly established and requires further research.

The natural level of IGF-1 in a cow's milk is influenced by several factors, including the cow's breed, its stage of lactation, its diet, and the presence or absence of rBGH treatment.