A2 milk & beta casein: What's the buzz?

Christine Page

As Custard, one of our A2 Jersey heifers, approaches her calving date, here’s the latest on A2 milk and beta casein.

Milk is one of nature's most perfect foods, thanks to its combination of essential vitamins, minerals, proteins, healthy fats and milk sugars. And when your milk is raw from healthy and contented 100% grass-fed cows (like Custard), its enzymes and probiotics also aid digestion and the effective absorption of nutrients.

However, not all cows are the same, not even 100% grass-fed cows. A millennia-old genetic mutation could be affecting their milk proteins, which, in turn, might affect how we digest the milk…

The background

All cows milk contains six proteins: two whey proteins and four casein proteins, with the latter making up the majority. Beta casein makes up a third of the casein proteins, the equivalent to around two teaspoons per litre of milk.

All proteins are made up of long chains of amino acids and beta casein has a chain of 209. During digestion in the gut, enzymes break down the amino acids by interacting with them at specific locations on the protein chain. Position 67 in beta casein’s chain is one such location, and herein lies the rub. 

All native African and Asian cattle, from which all European cattle originate, are genetically predisposed to have at position 67 a proline amino acid, giving them what's called A2 beta casein. These cows carried the A2 gene.

Between 5,000 – 10,000 years ago, cattle were progressively being taken north into Europe. At some point, a mutation occurred in some cattle at position 67 and the proline was replaced by a histidine amino acid, so they then produced what's called A1 beta casein. These cows then carried the A1 gene.  

As with all genes, one allele comes from each parent. Thus:

  • A cow that takes the A1 gene from each parent produces only A1 beta casein: an A1/A1 cow.
  • A cow that takes A1 from one parent and A2 from the other, produces both A1 and A2 beta casein: an A1/A2 cow.
  • A cow that takes A2 from both parents produces only A2 beta casein: an A2/A2 cow.

So as cows produce off-spring and those are subsequently bred, either the A1 or A2 gene is passed down through the generations.

A consequence of the mutation, and the unwitting selection criteria for which cows to breed, has been an increase in the number of cows carrying the A1 gene. Today most European, US, NZ and Australian cows, especially the high-producing black and white cows like Holsteins that are the mainstay of modern day commercial milk production, carry only the A1 gene. 

It’s easy to find out which gene a cow carries with a simple DNA test of a tail hair sample. 

Histidine A1 vs Proline A2

Histidine is in fact an essential nutrient. The body uses it to make histamine, which we know is produced in response to injury and allergic and inflammatory reactions. Aha! I hear you say (as I initially did) it’s all that histamine rushing round our bodies causing havoc!

It seems not, we need to dig a little deeper: the digestive enzymes that break down proteins interact with beta casein precisely at the location where histidine has replaced proline, so A1 and A2 beta casein proteins are processed in our gut differently. 

A1 beta casein digests to release a peptide (a protein fragment) that has opioid characteristics. The peptide is called beta-casomorphin-7, or BCM7. This translates as ‘a morphine-like fragment from beta-casein containing seven amino acids’.

The enzymes cannot cut the A2 protein in the same way. Thus, BCM7 is not formed from A2 proteins.

Beta-casomorphin-7: the devil in the milk

Prof Keith Woodford of Lincoln University in New Zealand wrote a book called Devil in the Milk back in 2007. The book makes compelling reading but at the time human clinical trials were missing and the dairy industry did their best to discredit his work. However, since then the evidence has been mounting and in the past three years several peer-reviewed research papers have been published showing a marked difference between A1 and A2 milk.

In this study, a randomised, double blind, cross-over trial, consumption of A1 beta casein resulted in increased gastrointestinal inflammation, worsening of post-dairy digestive discomfort symptoms, delayed transit, and decreased cognitive processing speed and accuracy. In layman’s terms: stomach ache, constipation and feeling groggy.

This study showed that one of the reasons A1 milk can cause such problems is that BCM7 activates opioid receptors expressed throughout the gastrointestinal tract and body.

The research also suggests that a proportion of people who believe they have lactose intolerance may in fact be sensitive to A1 beta casein. There are a number of other more serious health issues that Prof Woodford suggests may be linked to A1 milk but these are yet to be proven by human trials. 

It’s worth noting, that sheep, goats, camels and humans all carry only the A2 gene. 

Which brings us back to the lovely Custard, who is one of our A2/A2 Jersey cows. All being well, her calf will be born in mid-February and we are looking forward to sharing with it Custard’s special A2 grass-fed, organic, antibiotic-free raw milk. If you can't tolerate milk from ‘normal' cows, A2 milk like Custard's might be worth a try. 

We milk each of our cows separately, so look out for the special A2 label (and the individual cow's name) on the bottles in our Farm Shop milk fridge.

Find out here how to order your milk.