A2A2. You've heard the term, started researching it and ended up here.
So what exactly is A2A2 milk? When people refer to the term A2, they're talking about a variant of beta-casien protein found within the milk at a molecular level. When someone says "A2 milk" they're referring to the specific type of beta-casein protein that makes up that milk.
The California Dairy Research Association gives us a history lesson and explains the A2A2 debate:
According to the literature, more than 10,000 years ago, and before they were domesticated, cows produced only the A2 beta casein protein and not the A1 beta casein protein. However, some 8,000 years ago a natural single-gene mutation occurred in Holsteins, resulting in production of the A1 beta casein protein in this breed. This mutation in the beta casein gene led to 12 genetic variants, of which A1 and A2 are most common. The mutation was passed on to many other breeds, principally because Holsteins are used to genetically improve the production of other breeds. Slowly, the A1 beta casein variant became dominant in milk. While dairy herds in much of Asia, Africa, and part of Southern Europe remain naturally high in cows producing A2 milk, the A1 version of the protein is common among cattle in the Western world.
A point of reference is that A2 milk products are made from dairy cows that produce only the A2 beta casein protein, whereas today’s cow’s milk contains both A2 and A1 beta casein proteins. The most common variants among Western cattle are A1, A2, and B.
In general, milks from Guernsey, Jersey, Asian herds, human milk, and others (sheep, goat, donkeys, yaks, camel, buffalo, sheep, etc.) contain mostly A2 beta casein. Milks from Holstein Friesian contain mostly A1 beta casein. The Holstein breed (the most common dairy cow breed in Australia, Northern Europe, and the United States) carries A1 and A2 forms of beta caseins in approximately equal amounts. More than 50 percent of the Jersey breed carries the A2 beta casein variant, but with considerable variation among the herd, and more than 90 percent of the Guernsey breed carries the A2 beta casein variant.
The debate about the A1 versus A2 milk goes back to the late 1980s. Consumption of regular cow’s milk containing both the A1 beta casein and A2 beta casein variants has been implicated in the development of Type 1 Diabetes, coronary heart disease (CHD) and, possibly, schizophrenia and autism in people with immune deficiencies. [The arguments] are not that A1 milk causes these illnesses, but rather that A1 beta casein is digested in a different way compared to A2, resulting in the release of a peptide (a protein fragment) from beta-casomorphin-7 (BCM-7). If BCM-7 gets through the gut and into the blood of people with immune deficiencies, they may experience negative health effects.
Therefore, the consumption of A1 beta casein has been brought to the public attention in particular in New Zealand and Australia.
A2 milk is being marketed as a healthier choice compared to regular milk. The A2 Milk Company claims that a quarter of milk consumers in Western countries report some kind of discomfort after drinking regular milk, citing a 2010 paper from the Innovation Center for U.S. Dairy. The A2 Milk Company says benefits of its dairy products include easier digestibility for people who are perceived to be lactose intolerant.
UC Davis gives us more insight: The solids found in cow’s milk are composed of fat, protein, lactose and minerals. Beta-casein is one of six milk proteins and is produced by the CSN2 gene. Fifteen genetic variants of CSN2 are known which cause changes of certain amino acids in the beta-casein protein and alter its properties. Based on the amino acid in position 67 these variants can be classified into 2 groups - A1 and A2. Variants that belong to the A1 group (His67) are A1, B, C, F and G. Variants that belong to the A2 group (Pro67) are A2, A3, H1, H2, I, J, K and L. The levels of bioactive peptide beta-casomorphin 7 (BCM7) produced from the metabolism of beta casein is several-fold higher for variants in the A1 group than in the A2 group. Higher levels of BCM7 have been associated with negative health effects in humans.
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. S Jianqin, X Leiming, S Lu, GW Yelland, J Ni and A Clarke. Nutrition Journal 2016:15-35.DOI: 10.1186/s12937-016-0147-z https://nutritionj.biomedcentral.com/articles/10.1186/s12937-016-0147-z
A2 Milk, Farmer Decisions, and Risk Management. Woodford, Keith. 2007. Proceedings of the 16th International Farm Management Association Congress, Peer Reviewed Papers Vol2, pp 641-648. University College, Cork, July 2007. (Eds S. O’Reilly, M. Keane, P. Enright. ISBN:978-92-990038-3-1). https://researcharchive.lincoln.ac.nz/handle/10182/417
Health implications of milk containing beta-casein with the A2 genetic variant.Bell SJ, Grochoski GT, Clarke AJ. Crit Rev Food Sci Nutr. 2006;46(1):93-100. http://www.ncbi.nlm.nih.gov/pubmed/16403684
Polymorphism of bovine beta-casein and its potential effect on human health.Kaminski S, Cieslinska A, Kostyra E J. Appl. Genet. 2007;48(3):189-98. https://www.ncbi.nlm.nih.gov/pubmed/17666771