A2 Milk by Donagh Berry
Approximately 25-30% of cow’s milk is beta-casein (ß-casein). There are several types of ß-casein, the most common of which are A1 and A2 – other types include A3, B, C, D, E, F, G, H1, H2, and I. It is thought that the A2 variant was the original variant with the A1 mutation originating approximately 5,000 to 10,000 years ago. A2 milk currently commands twice the price of regular milk in the southern hemisphere, and this milk type is now migrating onto European and US supermarket shelves. The question remains, is A2 milk the next trend in dairy? This was the question posed at the recent VistaMilk A2-milk Masterclass held in Teagasc Moorepark for Vistamilk members.
A1 milk and human health – ß-casomorphin (BCM-7)
There is a hypothesis that consumption of the A1 ß-casein has unfavourable health implications, most notably increasing the incidence of Type-I diabetes, ischaemic heart disease (the major cardiovascular disease) and as well as intensifying the symptoms of some neurological conditions such as autism, schizophrenia, post-partum depression, and sudden infant death syndrome.
Digestion of A1 ß-casein in the human small intestine releases a bioactive seven-amino-acid peptide, ß-casomorphin (BCM-7) which is known to have opioid properties. The hypothesis of the impact of BCM-7 on human health is that BCM7 enters circulation in susceptible people and suppresses immune surveillance or response to antigenic agents as well as possibly crossing the blood:brain barrier and influencing neurological function. Any effect of BCM-7 on human health is thought to only exist is individuals suffering from “leaky gut” which includes infants as well as possibly people on antibiotics; coeliacs are also thought to be potentially at risk.
The scientific evidence to support most of these hypothesise is, however, at best, weak. As was demonstrated in the European Food Safety Report (2009), a causal relationship could not be established between the consumption of the BCM-7 and the incidence of the various pathologies. On top of this Dr Ian Givens at the recent VistaMilk A2 Milk Masterclass in Moorepark presented results from published studies using animal models to examine the impact of A2 or A1 milk on a variety of pathologies such as diabetes, cardiovascular diseases and Neurological disorders. For each of these pathologies, no difference between A1 and A2 milk was observed, or the trends were far from conclusive; evidence that A1 beta-Casein is related to schizophrenia is very scant.
A2 milk and the cow
The difference between whether a cow produces A1 and A2-type milk is simply one DNA variant within the whole three billion pieces of DNA. The variant is called a SNP (pronounced “snip”) and we know where that DNA variant is. All animals genotyped in Ireland have information on whether or not their animals carry that DNA variant. The DNA variant is directly inherited from the parents and is also directly transmitted to the offspring. There are three possible genotypes of cows for the A2-type milk. The frequency of variants in Irish cows is in the Table below. A1A1 cows are those that have two copies of the A1 variant and they produce only A1-type milk. A2A2 cows are cows that have two copies of the A2 variant and only produce A2-type milk. A1A2 cows produce a mixture of A1 and A2 milk.
Preliminary Teagasc analysis 10 years ago revealed that the A2 variant is associated with higher milk yield and protein yield but not unfavourably associated with any other known trait routinely measured in Ireland. However, because the beta-casein gene resides close to other genes, such as the kappa-casein gene, associations between granular measures of milk quality are likely to exist and further investigations are merited. At the VistaMilk A2-milk masterclass, Dr Henk Bovenhuis from Wageningen University demonstrated that selection of cows for the A2 beta-casein variant has been associated with positive impacts on milk fat and protein yield, but a reduction in kappa-casein content which can have repercussion for the renneting characteristics of milk. Such results highlight there may be downstream processing considerations should an industry decide to migrate to an A2 herd.
A2 milk and VistaMilk
Vistamilk is a recently funded centre based at Teagasc, Moorepark with over 40 industry partners. It aims to digitalise dairy production and processing in Ireland all the way from the soil, through to the grass and animal, and eventually into the milk and resulting products while considering the impact at the level of the human gut. The centre will develop advanced sensing, communication and analytical solutions to current and future problem statements across the dairy-food chain; the pillars of focus include the 1) soil and pasture, 2) cow (i.e., genetics and management) and 3) food. By always considering the entire production chain, any potential upstream and downstream ramifications of modifications in any link along the chain can be readily quantified. This is important from the perspective of A2 milk which is dictated solely by one genetic variant but can have downstream ramifications for processing capabilities and eventual human health.
VistaMilk plans to carry out research to address some of the unknowns and ambiguity around A2 milk to enable farmers, processors and consumers to make more informed decisions. This includes the impact on genetic gain from selection on the A2 beta-casein variant but also the impact, if any, on the processability of the milk. While the immediate focus is on A2 milk, all other genetic variances in the different caseins (e.g., kappa-casein) and other milk-related genes (e.g., beta-lactoglobulin) will also be interrogated.
In conclusion, there is limited robust scientific evidence to support any claims related to the consumption of A2 dairy products. Such claims in the past have been paramount in the innovation and formulation of new dairy products. Therefore, if A2 is to become the next dairy trend, at present, this will be driven more by consumer perception, indulgence and marketing than by science. Nonetheless, any recommendation to remove milk products from the human diet, as a source of other valuable nutrients, could be more harmful than good. Dr Marianne Walsh from the Irish National Dairy Council outlined at the VistaMilk A2 Masterclass that market research on A2 milk in Ireland is limited. Therefore, it is plausible to assume that the Irish consumer is relatively unaware of A2 milk, but that the production of A2 dairy products could fill a niche.