For more information on Beta-Casein click here


What is a2 Milk?

Cow’s milk contains different types of protein.  Beta-casein comprises approximately 30% of the protein contained in cow’s milk.  There are two major genetic variants of beta-casein: A1 and A2.   

The A2 form of beta-casein has been identified as the original form of beta-casein that would have been produced by cows thousands of years ago.  A natural genetic variance occurred in European dairy herds, resulting in a variation of the A2 gene called A1 beta-casein – today most dairy milk contains a mixture of A1 and A2 beta-casein protein.  However, some dairy cows still only produce the A2 type of beta-casein and these can be identified by DNA testing and milked to produce a2 Milk.


How is a2 Milk different?  

a2 Milk is produced by cows which produce the A2 type of beta-casein exclusively. The A1 beta-casein type is digested differently to the A2 type due to a difference in a single amino acid at position 67 on the protein chain.   A1 beta-casein has the amino acid histidine at position 67, while A2 beta-casein has a proline amino acid in the same position (Figure: 1). Human milk also contains proline at the equivalent position.  A1 beta casein releases the opioid peptide beta-casomorphin-7 (BCM-7) upon digestion whereas A2 beta-casein does not or if it does, it does so at a very low rate.

Figure 3 

Potential impact of beta-casein on health

Epidemiological evidence suggests that A1 beta-casein is a possible risk factor in the development of type 1 diabetes mellitus in children and ischaemic heart disease in adults.   A2 beta-casein has not been linked to these conditions.

Evidence suggests that beta-casomorphins, which are a byproduct of A1 beta-casein, have various effects on the gastrointestinal tract including inhibition of gastrointestinal motility.

There is significant interest in a gluten and casein free diet for people with autism as some have reported improvements in symptoms of autism after following such a diet. It is proposed that derivatives of gluten (glutomorphins) and casein (casomorphins) may cross into the brain and alter brain and neural activity. The A1 beta-casein variant releases the exogenous opioid peptide beta-casomorphin-7 (BCM-7) following normal enzymatic digestion, whereas A2 beta-casein does not, or if it does, it happens at a very low rate.  Hence, there may be a potential role for a2 Milk in this condition.  Adequately powered randomized controlled trials are needed, however, to determine the impact of such diets in people with autism. 

A European study of infant formula subjected to simulated gastro-intestinal digestion (SGID) has shown that BCM-7 is released from the A1 but not the A2 type of beta-casein protein in 800mL of various commercial infant formulae containing both beta-casein types during the SGID (800mL is an average daily recommended intake for an infant. However, the significance of this in infant health remains unknown.

The European Food Safety Authority has acknowledged that BCM-7 is an opioid that could affect a range of cells and tissue, including the digestive and immune systems, but that there was a need for further research to determine a causal link between A1 beta-casein consumption and disease.


Click here for further information on Beta-casein Variants: The Science 

Click here for further information on Beta-casein Variants and Post Dairy Discomfort

Click here for further information on Beta-casein Variants, Beta-casomorphin-7 and Infants


Disclaimer: This resource is sponsored by A2 Dairy Products Australia.  The information contained within this document is intended for health care professionals and should not be construed as professional medical advice nor as any health claim associated with consuming a2 milk™.