Does A2 milk cause cholesterol? Unpacking the science behind milk proteins and heart health

October 29, 2025 •

4 min read

While some older epidemiological studies associated A1 beta-casein consumption with heart disease risk, human trials have found no evidence that A2 milk exerts a different effect on plasma cholesterol compared to A1 milk. The conversation surrounding whether A2 milk causes cholesterol is nuanced and requires a closer look at the science.

Quick Summary

The protein type in milk (A1 or A2) does not have a differential impact on blood cholesterol levels in humans. Saturated fat content, determined by the milk's processing (e.g., whole vs. low-fat), is the primary dietary factor that can influence cholesterol.

Key Points

A1 vs. A2 Protein: A1 and A2 milk contain different beta-casein protein variants, with A1 potentially releasing a peptide (BCM-7) during digestion, which was linked to some health concerns in early research.
Human Studies Show No Difference: Randomized controlled trials in humans have found no differential effect on total, LDL, or HDL cholesterol levels when comparing diets containing A1-dominant versus A2-dominant milk.
Fat Content is the Key: The primary factor influencing milk's effect on cholesterol is its fat content (whole, low-fat, or skim), which determines the amount of saturated fat consumed.
Older Research was Limited: Early epidemiological and animal studies that suggested a link between A1 protein and heart disease were not conclusive and did not prove causation, failing to hold up in later human trials.
Focus on Overall Diet: A holistic approach to diet and heart health, including choosing low-fat dairy and reducing overall saturated fat intake, is more effective for cholesterol management than worrying about the A1/A2 distinction.
Food Matrix Matters: The effect of dairy on cholesterol is complex and depends on the entire 'food matrix,' as shown by studies comparing butter and cheese, which have different impacts despite similar saturated fat levels.

A Tale of Two Proteins: Understanding A1 and A2 Beta-Casein

To understand if A2 milk affects cholesterol, one must first grasp the difference between A1 and A2 beta-casein, the two protein variants found in cow's milk. The distinction lies in a single amino acid difference at position 67 of the protein chain.

A1 Beta-Casein: Found predominantly in milk from breeds of cows originating from Northern Europe (e.g., Holstein-Friesian, Ayrshire), the A1 variant has a histidine amino acid at position 67. During digestion, this protein can break down to produce a peptide called beta-casomorphin-7 (BCM-7).
A2 Beta-Casein: This is the older, original form of beta-casein and is found in milk from older cow breeds like Jersey, Guernsey, and zebu, as well as human and goat milk. The proline amino acid at position 67 holds the protein chain more tightly, preventing the release of BCM-7.

The A1-A2 Cholesterol Hypothesis: From Rabbits to Humans

The theory linking A1 milk to cardiovascular disease emerged from observational studies and animal research. Early epidemiological research noted correlations between populations with higher A1 milk consumption and higher rates of ischemic heart disease mortality. This was followed by a rabbit study where those fed A2 beta-casein had lower serum cholesterol and less arterial thickening than those on an A1 beta-casein diet. These early findings sparked significant public interest and led to the marketing of A2 milk as a healthier alternative.

However, the scientific community emphasizes caution, noting that observational studies do not prove causation, and animal studies do not always translate to human results. When human randomized controlled trials (RCTs) were conducted to test this hypothesis, the results were consistently different from the initial animal and epidemiological findings.

What the Human Trials Revealed

In a landmark 2006 randomized crossover trial involving 62 participants, researchers compared the effects of A1-dominant and A2-dominant milk and cheese on plasma cholesterol levels over two 4.5-week periods. The study found:

No statistically significant difference in mean plasma total cholesterol, LDL cholesterol, or HDL cholesterol between the A1 and A2 diets.
The researchers concluded there was "no evidence that dairy products containing beta-casein A1 or A2 exerted differential effects" on plasma cholesterol in humans.

This key human study, along with other reviews, has shown that the protein variant does not play a significant role in determining a person's blood cholesterol levels.

Comparison of A1 Milk vs. A2 Milk on Cholesterol


Feature	A1 Milk	A2 Milk
Protein Type	Contains the A1 beta-casein protein variant.	Contains only the A2 beta-casein protein variant.
Beta-Casomorphin-7 (BCM-7)	Releases BCM-7 during digestion, which has been the subject of some early health concerns, though largely unsubstantiated by human studies.	Does not release BCM-7 during digestion due to a stronger protein structure.
Impact on Cholesterol	Human randomized trials show no evidence of differential effects on total, LDL, or HDL cholesterol levels compared to A2 milk.	Human randomized trials show no evidence of differential effects on total, LDL, or HDL cholesterol levels compared to A1 milk.
Key Factor Affecting Cholesterol	The fat content (whole, low-fat, skim) and overall dietary saturated fat intake are the crucial variables for cholesterol levels.	The fat content (whole, low-fat, skim) and overall dietary saturated fat intake are the crucial variables for cholesterol levels.
Source Cows	Common in European breeds like Holstein-Friesian.	Predominant in older breeds like Jersey, Guernsey, and certain Asian and African cattle.

The True Dietary Impact on Cholesterol: Focus on Fat Content

So, if the protein type doesn't matter for cholesterol, what does? The primary dietary factor influencing milk's effect on cholesterol levels is its fat content, not the A1 or A2 protein variant.

Saturated Fats: Whole milk is higher in saturated fat than low-fat or skim milk. Diets high in saturated fat are known to raise LDL ("bad") cholesterol levels. Therefore, whole A2 milk, just like whole A1 milk, will have a different impact on blood lipids than its low-fat counterpart.
Food Matrix Effect: More recent research has moved beyond focusing on single nutrients like saturated fat or cholesterol in dairy. Instead, the concept of the "food matrix" is considered, which is the sum of all nutrients and how they interact. For example, studies have shown that the impact of dairy fat on cholesterol can differ depending on whether it comes from butter versus cheese. This suggests the full context of the food matters more than isolating one component.

Strategies for a Cholesterol-Conscious Diet

For those looking to manage or reduce their cholesterol, focusing on overall diet and lifestyle is far more effective than worrying about the A1 or A2 protein type. Here are some actionable steps:

Choose Low-Fat Dairy: Opt for low-fat or skim versions of milk, yogurt, and cheese to reduce saturated fat intake without sacrificing nutrients like calcium and protein.
Increase Soluble Fiber: Incorporate foods rich in soluble fiber, such as oats, apples, beans, and barley. This type of fiber can help reduce the absorption of cholesterol into your bloodstream.
Eat Healthy Fats: Replace saturated and trans fats with unsaturated fats. Good sources include avocados, nuts, seeds, and olive oil.
Focus on Whole Foods: A diet rich in fruits, vegetables, whole grains, and lean proteins is a cornerstone of heart health.
Stay Active: Regular physical activity helps increase HDL ("good") cholesterol and lower triglycerides.

Conclusion

The scientific consensus, based on human clinical trials, is that there is no meaningful difference in how A1 and A2 milk affect cholesterol levels. Concerns initially raised by older observational studies and animal research were not substantiated by more robust human studies. The milk's fat content, rather than its protein variant, is the determining factor for its impact on blood lipids. Ultimately, individuals concerned about cholesterol should focus on a holistic approach to diet and lifestyle, including choosing low-fat dairy options and reducing overall saturated fat intake, rather than fixating on the A1 versus A2 debate.

For a more detailed analysis of the human trial on A1 and A2 casein, see the original study abstract here.

Frequently Asked Questions

No, the fat content of milk is determined by whether it is whole, low-fat, or skimmed, not by the A1 or A2 protein variant it contains. Whole A2 milk has the same fat content as regular whole milk.

The main difference is a single amino acid in the beta-casein protein. A1 beta-casein can release the peptide BCM-7 during digestion, while A2 beta-casein does not.

Some proponents suggest A2 milk may be easier to digest for those with milk sensitivities, but scientific evidence is still limited. It is not a cure for lactose intolerance or a milk allergy.

Human trials have not shown a cardiovascular advantage to choosing A2 milk over regular A1 milk. Concerns about A1 protein's impact on heart health have not been substantiated in human studies.

Whole A2 milk, like any whole milk, contains saturated fat that can raise cholesterol levels. The A2 protein itself does not cause cholesterol to rise; the fat content is the influencing factor.

If you have high cholesterol, it is more important to focus on the milk's fat content rather than the protein type. Choosing low-fat or skim A2 milk is a better option than whole milk.

For the specific question of cholesterol, human clinical trials have shown no differential effect between A1 and A2 milk. While early epidemiological findings suggested a link, later trials did not support it. The general consensus is that the distinction is not as significant as once hypothesized.