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A1 VERSUS A2 MILK - THE HEALTH THREAT
Milk from dairy cows has been regarded as nature's perfect food, providing an important source of nutrients including high quality proteins, carbohydrates and selected micronutrients.
More than 95% of the cow milk proteins are constituted by caseins and whey proteins. Among the caseins, beta casein is the second most abundant protein and has excellent nutritional balance of amino acids.
Different mutations in bovine beta casein gene have led to 12 genetic variants and out of these A1 and A2 are the most common. The A1 and A2 variants of beta casein differ at amino acid position 67 with histidine (CAT) in A1 and proline (CCT) in A2 milk as a result of single nucleotide difference.
This polymorphism leads to a key conformational change in the secondary structure of expressed β-casein protein. Gastrointestinal proteolytic digestion of A1 variant of β-casein (raw/processed milk) leads to generation of bioactive peptide, beta casomorphin 7 (BCM7). Infants may absorb BCM-7 due to an immature gastrointestinal tract whereas adults gather the biological activity locally on the intestinal brush boarder. In hydrolysed milk with variant A1 of beta-casein, BCM-7 level is 4-fold higher than in A2 milk. Initial studies on indigenous cow (Zebu type), buffalo and exotic cows (taurine type) have revealed that A1 allele is more frequent in exotic cattle while Indian native dairy cow and buffalo have only A2 allele, and hence are a source for safe milk.
Recently, a relationship between disease risk and consumption of a specific bovine β-casein fraction with either A1 or A2 genetic variants has been identified. BCM7 is suggested to be associated as a risk factor for human health hazards as it can potentially affect numerous opioid receptors in the nervous, endocrine and immune system. It is also known to be an oxidant of low dietary lipoproteins (LDL) and oxidation of LDL is believed to be important in formation of arterial plaque. Epidemiological evidences claim that consumption of beta-casein A1 milk is associated as a risk factor for type-1 diabetes, coronary heart disease, arteriosclerosis, sudden infant death syndrome, autism, schizophrenia etc.[3,4] A broad range of studies from American and European investigations has shown reduction in autistic and schizophrenic symptoms with decrease in A1 milk intake. Further, animal trials have also supported the linking of type-1 diabetes to milk exposure in general and A1 beta-casein in particular.
Populations, which consume milk containing high levels of β-casein A2 variant, have a lower incidence of cardiovascular disease and type-1 diabetes. The A1/A2 hypothesis is both intriguing and potentially very important for public health if it is proved correct. It should be taken seriously and deeper research is needed to verify the range and nature of BCM7 interactions with the human gastrointestinal tract and whole organism. This requires more of animal trials and generation of data on human subjects having the problems related to A1/A2 beta-casein milk consumption.
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A2 Milk Facts
February 9, 2017
By Gonca Pasin, Ph.D.
What is A2 Milk?
A2 milk is cow’s milk that contains only the A2 variant of beta-casein protein. In referring to A2 milk, we are talking only about the specific type of protein it contains, called beta casein, and nothing else (not fat or carbohydrates).
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.
Two major protein groups are present in cow’s milk – approximately 82 percent of protein is casein and approximately 18 percent is whey protein. Both groups have excellent nutritional benefits.
Caseins are a group of proteins. Among the caseins, beta casein is the second most abundant protein (about one-third of the caseins) and has an excellent nutritional balance of amino acids.
The beta casein group has two common variants: A1 and A2 beta casein. Most milk contains a mixture of these proteins. Approximately 60 percent of the beta casein is A2, and 40 percent is A1.
The proportion of A2 and A1 beta casein in milk can vary with different breeds of dairy cattle – A2 milk contains only A2 beta casein.
Marketing of A2 Milk
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. Claims have been made that A2 milk is benign in this respect. However, these arguments—strongly advanced by proponents of the benefits of A2 milk—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, where A2 milk is marketed by the A2 Milk Company (previously A2 Corporation) as being a lower risk factor for disease development. However, the suggestions that A2 beta casein provides levels of protection from developing schizophrenia, autism, diabetes, and CHD are unproven.
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.
In summary, despite the A2 Milk Company’s claims that many studies support the health benefits of A2 milk, the scientific evidence is very thin. The human clinical studies conducted to date do not provide evidence of any benefit of A2 milk.
The strongest evidence for any possible benefit of A2 milk are the rat studies that demonstrate BCM-7, which is released during digestion of the A1 beta casein variant, causes inflammatory immune response.
The majority of science communities agree that there is a lack of evidence to prove A2 milk is better for health, and A2’s beneficiary effects are anecdotal and not based on credible evidence.
Despite published studies evaluating the benefits of milk solely containing A2 proteins, no convincing evidence demonstrates its benefits over consumption of milk and dairy products containing a combination of A1 and A2 beta casein.
Current science supports the continued consumption of cow’s milk and dairy products.
All cow’s milk provides complete nutrition for infants. It contains the essential micronutrients needed for growth and development of human health, as well as for the neonate animal.
All cow’s milk naturally provides nine essential nutrients in one tasty, convenient, and affordable package. Whichever milk you choose, you are doing your health a favor.
All cow’s milk is part of a balanced diet, and a good source of many different nutrients. Milk containing predominantly A2 beta casein is as safe and wholesome as any other milk.
The 2015 U.S. Dietary Guidelines for Americans recommends three servings a day of dairy foods as part of a healthy, balanced diet.
-Gonca Pasin, RD, Ph.D., is the executive director at the California Dairy Research Foundation (CDRF), based in Davis, Ca. The California Dairy Research Foundation is a nonprofit research management organization that leads and delivers research and science-based programs to support a more innovative and sustainable California and U.S. dairy industry. For more information about the CDRF, visit www.cdrf.org.