What are A1 and A2 milk? Does it matter which one we consume?

Health and Nutrition

Milk is an essential part of our food culture and it is a beverage that provides essential macronutrients and micronutrients. It plays a valuable part in our balanced diet. Milk is a fluid which is made up of almost 88 % water and the remaining 11 to 12 % consists of all the other constituents.

Milk is also used to make several other products such as cream, butter, curd/yogurt, ghee, kefir and cheese which are consumed all over the world. It is such a versatile food that it can be made into so many products and that makes consumption of milk quite interesting.

Composition of milk

The major component of milk is water which is about 88 %. Milk also contains protein 3.15 %, lipids 3.25 % and carbohydrates 4.8 % (1). It is a good source of several minerals such as calcium, phosphorus and vitamins like vitamin A, vitamin D, choline and vitamin B12.


What are A1 and A2 milk?

About 80 % of the total protein in milk is casein (2). Casein is made up of 36% α-Casein, 27% β-Casein, 9% κ-casein and 27% peptides and amino acids. That makes beta-casein the second major protein in milk. Over time because of mutations of beta-casein gene 12 genetic variants have come into existence. Among these 12 genetic variants, A1 and A2 are the most common (3).

The difference between A1 and A2 variants is because of the change in one nucleotide at the 67 th position, A1 has histidine and A2 has proline (2). The difference is because of the variation in a single nucleotide.

Before the cows were domesticated, they gave milk which has A2 beta-casein and no A1 beta-casein. Over time natural mutation occurred and a proportion of European cows started producing milk containing A1 beta-casein variant. Slowly over a period of time, A1 beta-casein variant became more dominant in the milk of many crossbred cows such as Holstein, Jersey and Friesian (4).


A1 and A2 milk and their effect on health:

A1 milk is regular milk which contains both A1 and A2 beta-casein. A2 milk contains only A2 beta-casein. Betacasomorphin7 (BCM7) is an opioid peptide that is released when A1 beta-casein is digested. This opioid peptide is thought to be the reason why A1 milk is considered to be less healthy (3). BCM7 is a 7 amino acid bioactive peptide (4).

The BCM7 peptide seems to have the ability to affect a number of opioid receptors in the nervous, endocrine and immune system (3). An immature gastrointestinal system of a baby may make it possible to absorb these peptides while these peptides may show their effect on the gastrointestinal system in adults (4).

This bioactive peptide β-casomorphin-7(BCM-7) which is released during digestion of A1 beta-casein is linked to many diseases such as (4)

  • Type 1 diabetes
  • Autism
  • Schizophrenia
  • And heart diseases

A2 milk, on the other hand, has not been linked to any of these diseases.

There is evidence that A1 beta-casein derivative peptide BCM-7 is pro-inflammatory (5). The same was not found with A2 milk. Those people with lactose intolerance and other digestion problems can switch to A2 milk because A1 milk seems to cause inflammation and bloating. Because in a study by removing A1 milk from diet there was a decrease in some symptoms (6).

People with digestive problems especially connected to inflammation can stop A1 milk and start using only A2 milk and see if it helps.

According to a critical review, the conclusion was that A2 milk or desi cow’s milk should be the only milk recommended as it prevents us from getting any diseases related to A1 milk consumption (3). They also suggest to stop crossbreeding programs of cows and preserve the purity of desi breeds.


Final word:

There is evidence which has been building up that A1 milk consumption may have an adverse effect on health because it may trigger some chronic diseases. But most of the studies are in animals.

But the evidence is not conclusive in human studies. The A1 vs A2 debate is still going on and the literature available is inconclusive. Therefore, at this point, it can be suggested that if there is a way to get only A2 milk for yourself then go ahead.



  1. United States Department of Agriculture, USDA Food Composition Databases.
  1. Ahmet, F.D. and Bahattin, C. (2018) Discussions of Effect A1 and A2 Milk Beta-Casein Gene on Health, Appro Poult Dairy & Vet Sci. Vol. 3 (2).
  1. Jawale, B., Kaluskar, A., Garde, J. and Sabnis, S. (2017) The Reality of the White” A1 vs. A2 Milk- A Critical Review, International Journal of Science and Research (IJSR). Vol. 6(6).
  1. Boro, P., Naha, B., Saikia, D. and Prakash, C. (2016) A1 AND A2 Milk & Its Impact on Human Health, International Journal of Science and Nature. Vol. 7.
  1. Taylor, S.B., Dwyer, K., Woodford, K. and Kost, N. (2017) Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein, Advances in Nutrition. Vol. 8(5).
  1. Jianqin, S., Leiming, X., Lu, X., Yelland, G. W., Ni, J. and Clarke, A. J. (2016) Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk, Nutrition journal. Vol. 15(35).

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