A1 and A2 milk differ in their protein content, specifically the type of casein. Some studies suggest that A2 may be healthier, but more research is needed.

Is it possible that the health effects of milk may depend on the breed of cow it came from? Maybe.

Researchers have identified differences in beta-casein, a protein found in bovine milk (cow’s milk). This type of protein makes up around 30% of the protein in milk.

There are two main types of beta-casein in milk, A1 β-casein and A2 β-casein. Different breeds of cows produce milk with A1 or A2 beta-casein. Though more research in humans is needed, researchers are investigating whether A2 milk may have more health benefits than regular A1 milk.

Research suggests that A2 milk may be easier for people with milk intolerance to digest, and some people think A1 milk may contribute to some chronic health conditions and disorders.

This article takes an objective look at the science behind A1 and A2 milk.

What is A1 and A2 milk?

Casein is the largest group of proteins in milk, making up about 80% of the total protein content. There are several types of casein in milk. Beta-casein is the second most prevalent and exists in at least 13 different forms.

The two most common forms are:

  • A1 beta-casein: Milk from breeds of cows that originated in northern Europe is generally high in A1 beta-casein. These breeds include Holstein, Friesian, Ayrshire, and British Shorthorn.
  • A2 beta-casein: Milk that is high in A2 beta-casein is mainly found in breeds that originated in the Channel Islands and southern France. These include Guernsey, Jersey, Charolais, and Limousin cows.

Regular milk may contain both A1 and A2 beta-casein, but A2 milk contains only A2 beta-casein. Some studies suggest that A1 beta-casein may affect health and that A2 beta-casein may be a healthier choice, especially if you have difficulty digesting dairy products.

There is some public and scientific debate over these two types of milk. A2 milk is produced and marketed by the A2 Milk Company and contains no A1 beta-casein.

Research suggests that A1 beta-casein may contribute to adverse digestive symptoms like bloating, gas, and diarrhea in some people.

Lactose intolerance is the inability to fully digest milk sugar (lactose). This is a common cause of digestive discomfort and symptoms. The amount of lactose in A1 and A2 milk is the same. However, some people feel that A2 milk causes less bloating than A1 milk.

Some studies suggest that milk components other than lactose may cause digestive discomfort. Scientists have suggested that certain milk proteins may be responsible for some people’s milk intolerance.

One study in 41 people showed that A1 milk causes softer stools than A2 milk in some individuals, while another study in Chinese adults found that A2 milk led to significantly less digestive discomfort after meals.

Additionally, research suggests that A1 beta-casein may increase inflammation in the digestive system.

To understand the research surrounding A1 and A2 milk and what it may or may not mean for you and your health, you’ll need to understand some basics of research.

Much of the research surrounding A1 and A2 milk is “observational,” which means that a study is able to identify a group of people who are drinking A1 or A2 milk. The study may also identify health conditions that the group of people have, and the study may identify that more people who drank one type of milk have a specific health condition than those who drank a different type of milk. However, this type of study has limitations. Observational studies cannot determine something called “causation.”

For example, if an observational study notes that more people who drink A1 milk have purple hair than those who drink A2 milk, the researchers cannot determine that A1 milk causes purple hair or even that drinking A1 milk puts people at risk of having or developing purple hair. This is known as an association, and it’s an interesting thing to discover.

Associations can guide future research, helping to determine more about these associations and perhaps discovering a link to what might cause them.

Research suggests that a component in A1 milk, Beta-casomorphin-7 (BCM-7), may be associated with some adverse health claims. BCM-7 is an opioid peptide, a building block of proteins, that is released during the digestion of A1 beta-casein. It’s the reason why some people believe A1 milk may be less healthy than A2 milk.

Some studies suggest that BCM-7 may be linked to digestive problems and several other conditions, such as type 1 diabetes and heart disease.

However, there are other older studies that have found no connection or mechanism for A1 milk or BCM-7 to cause or contribute to these conditions. While BCM-7 may affect your digestive system, it’s still unclear to what extent BCM-7 is absorbed intact into your blood.

More recently, a test tube study found that the release of BCM-7 did not affect cells during digestion. These results suggest that A1 milk and BCM-7 may not cause health conditions.

While BCM-7 has been extensively researched, its overall health effects remain unclear.

However, though weak, some research suggests that A1 milk might be associated with health conditions like:

Type 1 diabetes

Type 1 diabetes is typically diagnosed in children and characterized by a lack of insulin. Some research suggests that drinking A1 milk during childhood might be associated with type 1 diabetes.

However, these studies are observational. They cannot prove that A1 beta-casein causes type 1 diabetes — only that those who are getting more of it may be at a higher risk.

Some animal studies have found no difference between A1 and A2 beta-casein. Initial animal studies suggested the opposite, that A1 beta-casein may have a protective effect against type 1 diabetes.

So far, no clinical trials in humans have investigated the effect of A1 beta-casein on type 1 diabetes. There is no evidence to support the claim that drinking A1 milk causes type 1 diabetes in some individuals.

Heart disease

Observational studies suggest A1 milk consumption may contribute to an increased risk of heart disease.

One test in rabbits showed that A1 beta-casein promoted fat buildup in injured blood vessels. This buildup was much lower when the rabbits consumed A2 beta-casein. Fat accumulation may potentially clog blood vessels and cause heart disease. Still, the human relevance of the results has been debated.

In one early study in 15 adults at high risk of heart disease, no significant adverse effects were observed. A1 and A2 had similar effects on blood vessel function, blood pressure, blood fats, and inflammatory markers.

Another early study found no significant differences in the effects of A1 and A2 casein on blood cholesterol.

More research in humans is needed to determine if A1 b-casein milk contributes to cardiovascular disease.

The debate about the potential health effects of A1 and A2 milk is ongoing. Research suggests that A1 beta-casein can cause adverse digestive symptoms in certain individuals.

But the evidence is still too weak for any solid conclusions to be made about the supposed links between A1 beta-casein and other conditions, such as type 1 diabetes and heart disease.

That said, A2 milk could be worth a try if you have trouble digesting cow’s milk.