Does Adding Milk to Coffee Reduce Polyphenols? The Science Explained

October 27, 2025 •

3 min read

For years, a persistent health myth suggested that adding milk to coffee neutralized its beneficial compounds, but new studies reveal a more complex interaction. Let's explore the science behind the question: does adding milk to coffee reduce polyphenols?

Quick Summary

The impact of adding milk to coffee on polyphenols is complex, with newer research suggesting potential anti-inflammatory benefits from the polyphenol-protein interaction.

Key Points

Polyphenol-Protein Binding: Milk proteins, especially casein, bind with coffee's polyphenols, a proven chemical interaction.
Enhanced Anti-Inflammatory Effects: New research shows the compounds formed by binding have twice the anti-inflammatory power of polyphenols alone in immune cells.
Bioavailability Not Nullified: While some initial absorption might be affected, overall bioavailability does not appear to be significantly compromised in human studies.
Complex Interaction: The effect of milk is not a simple reduction but a modification of the polyphenols' biological activity.
Health Benefits Remain: The latest evidence indicates that drinking coffee with milk still provides significant health benefits, possibly even enhancing some.

Unpacking the Polyphenol-Milk Interaction

Coffee is a rich source of polyphenols, powerful antioxidants known for their potential health benefits, including fighting inflammation. The common concern is that milk proteins, particularly casein, bind to these polyphenols, preventing their absorption and reducing their effectiveness. While initial studies provided conflicting results, a clearer picture is now emerging from recent research.

The Binding Effect: Fact or Foe?

Early in-vitro (test tube) studies confirmed that milk proteins bind to coffee's polyphenols, like chlorogenic acid. This interaction led some to theorize that the complex formed would render the polyphenols less bioavailable—meaning the body couldn't absorb them as easily. However, this simplified view didn't account for what happens during human digestion. More sophisticated studies simulating digestion and in-vivo (human) trials have painted a different picture.

The Anti-Inflammatory Synergy

In a landmark 2023 study published in the Journal of Agricultural and Food Chemistry, Danish researchers found that when polyphenols bind with the amino acids from milk, the resulting compounds were twice as effective at fighting inflammation in immune cells than the polyphenols alone. The interaction doesn't neutralize the antioxidant effect; it enhances the anti-inflammatory properties. This is a critical finding, suggesting that the protein-polyphenol bond can actually be beneficial, not detrimental.

Bioavailability: Is it Truly Reduced?

While some early in-vivo studies found lower urinary excretion of certain polyphenol metabolites when coffee was consumed with milk, suggesting reduced bioavailability, other research contradicts this. A study published on CoffeeScience.org revealed that after drinking coffee with milk, polyphenols still reached the bloodstream in equal amounts as when black coffee was consumed, albeit with a slight delay. Furthermore, a 2022 Food Chemistry study found that adding skimmed cow's milk significantly enhanced the in vitro bioaccessibility of coffee polyphenols by up to 64%. This suggests that the digestive process may break down the protein-polyphenol complexes, releasing the active compounds.

Comparison: Old Theory vs. New Findings


Aspect	Older Hypothesis (Based on In-Vitro)	Newer Research Findings
Polyphenol Status	Milk proteins bind to polyphenols, rendering them inactive or less bioavailable.	Polyphenols bind with milk amino acids, creating enhanced anti-inflammatory compounds.
Bioavailability	Reduced absorption due to binding, leading to less health benefits.	Conflicting evidence; some studies show little to no reduction in overall absorption.
Antioxidant Effect	Antioxidant capacity is masked or impaired by milk addition.	Anti-inflammatory and antioxidant effects are significantly enhanced through the binding process.
The Bottom Line	Adding milk is bad for the health benefits of coffee.	Adding milk can create a more potent anti-inflammatory compound without negating other benefits.

The Role of Specific Milk Components

Not all milk components interact with polyphenols in the same way. Caseins, the predominant milk protein, have a high affinity for polyphenols, but whey proteins and milk fat globules also play a role. Some research suggests that milk fat globule membrane components can also enhance the effects of coffee polyphenols on brain function. This complexity explains why results can vary depending on the type of milk used and the specific digestive conditions being studied.

Key Mechanisms in the Digestive Process

Polyphenols and milk proteins interact through non-covalent bonds, which are influenced by factors like pH and temperature. The acidic environment of the stomach and enzymatic activity in the intestines can alter or break down these bonds. The Danish study, which focused on the binding of polyphenols to amino acids, is particularly relevant as it explores the specific compounds resulting from this interaction, rather than just measuring overall antioxidant capacity. It offers a new perspective that the interaction itself creates a more biologically active compound.

Conclusion

While the idea that adding milk to coffee reduces its beneficial polyphenols persists, modern science offers a more nuanced and, for many coffee lovers, a reassuring perspective. The interaction between coffee's polyphenols and milk's proteins is not a simple case of one cancelling out the other. Instead, they can form new compounds with enhanced anti-inflammatory properties. While some studies show temporary changes in absorption rates, evidence suggests the overall health benefits of drinking coffee, whether black or with milk, remain largely intact. For those who enjoy a milky coffee, the latest science suggests that you can continue to enjoy your brew without sacrificing its healthy potential. You can learn more about this exciting study at the Journal of Agricultural and Food Chemistry.

Frequently Asked Questions

No, adding milk to coffee does not destroy its antioxidants. While the proteins in milk do bind with coffee's polyphenols, a 2023 study found that the resulting compound can have a significantly enhanced anti-inflammatory effect.

Some earlier studies suggested a reduction in bioavailability, but later research has shown that the overall amount of polyphenols eventually reaching the bloodstream is not significantly affected. The binding interaction changes the polyphenol's form, but it does not necessarily render it useless.

For most people, both black coffee and coffee with milk offer health benefits from their polyphenol content. The optimal choice depends on personal preference. The addition of milk may even provide a boost to the anti-inflammatory properties.

Coffee polyphenols interact with milk proteins, like casein, through non-covalent bonds. This binding can be influenced by factors such as temperature and pH. The compounds formed have been shown to have enhanced anti-inflammatory effects.

The 2023 study focused on the binding of polyphenols with amino acids. Since many non-dairy milks, like soy milk, also contain proteins and amino acids, researchers believe similar beneficial interactions could occur. More specific research may be needed, however.

No, not all polyphenols are affected equally. The specific type of polyphenol, its molecular structure, and the particular milk proteins involved can all influence the interaction. Chlorogenic acid, a major polyphenol in coffee, is a key focus of much of this research.

Researchers suggest that this enhanced anti-inflammatory effect might also occur when combining other protein-rich foods with polyphenol-rich fruits or vegetables, such as in a smoothie. The principle is a general one for protein-polyphenol interactions.