Discipline: dairy & health; Keywords: A1 & A2 milk, histidine, Holstein, BCM-7, autism, artherosclerosis; insulin dependent diabetes mellitus.
What is A1 and A2 milk: The difference is associated with variation in the protein composition of cow’s milk. Both A1 and A2 variants are proteins in the casein group which makes up about 80 % of the proteins. The two variants are almost identical apart from differing in one amino acid at position 67 of the polypeptide (amino acid chain): A1 has histidine whereas A2 has proline. Current dairy breeds differ in composition of A1 and A2 in their milk: the highest frequency of the A1 variant is observed in Holstein (0.31-0.66) and Ayrshire (0.43-0.72) and A2 in Guernsey (0.88 -0.97) and Jersey (0.49 -0.72). Being the most popular breed and providing the most milk, the Holstein does introduce a comparatively high proportion of A1 milk into the South African market.
Claims to the negative effect of A1 milk: This is associated with the histidine at position 67 of the polypeptide. When A1 milk products are digested, the histidine results in a cut of the polypeptide into a shorter peptide with seven amino acids. This peptide is called ß-casomorphin-7 (BCM-7). In the case of A2 milk the proline prevents a split at this site that prevents the BCM-7 to be released. BCM-7 is associated with opioid and cyto-modulatory properties that amongst others, could have inhibitory effects on the immune system. It has also been implied that A1 milk does not digest and absorb as easy as A2 milk and some have claimed that A1 or A1A2 milk may be associated with increased risk of developing Type 1 Diabetes, autism and schizophrenia as well as coronary heart disease. Most claims put the focus on BCM-7, which then suggests an investigation into its relationship with these diseases.
Outcomes of research on BCMs: The following gives a summary of research results:
- The presence of BCMs (e.g. BCM-7) or related peptides in unprocessed milk obtained from healthy cows has not been convincingly demonstrated. There is however evidence that proteases in fermented milk or cheese manufacture can potentially hydrolyze β-casein BCMs and further degrade these peptides to shorter-chain peptides, but heat treatment during processing does not appear to affect the occurrence of BCMs in the final products.
- Although cow BCM-7 can act as an opioid receptor as mentioned above, it is not a potent receptor as BCMs in some other food products.
- Peptides with more than three amino acids normally do not transport through the intestinal epithelium and therefore is unlikely to be transported to other organs; blood tests appear to support this argument as it is normally not picked up in the blood stream.
- In concert, opioid peptides, including BCM-7, are highly sensitive to hydrolysis by peptidase, thereby strongly limiting or preventing their transfer intact across the intestinal mucosa and the blood-brain barrier.
- A link between casein-derived peptides and autism in patients with increased intestinal permeability has been suggested. However, recent data do not provide any support for such a relationship, which is in line with the argument of unlikely transfer of BCM-7 across the blood-brain barrier.
- It has been suggested that BCM-7 might be atherogenic through an oxidative action on LDL, but no studies confirmed this. Similarly, the possibility that BCM-7 could contribute to an increased risk of atherosclerosis and cardio-vascular disease has been suggested, but the control of other contributing variables in the studies was poor.
- Some ecological studies have linked the intake of BCM-7 with insulin dependent diabetes mellitus. However, ecological studies have the shortcoming of being unable to establish a cause-effect relationship and they cannot adjust for possible confounding factors.
- In conclusion: none of the outcomes of studies done could either show a likelihood of a relationship or establish a cause-effect relationship between the oral intake of BCM-7 or related peptides and the aetiology and development of any of the suggested diseases.
Reasons for the Organised Dairy Industry’s position: Bearing in mind (1) the research evidence above, (2) the fact that milk presented to the consumer has mostly been processed in bulk from various sources, and (3) that even dairy breeds with comparatively high frequencies of A1, do contain A2, the Organised Dairy Industry cannot support any action to discredit A1 milk or promote A2 milk at the expense of A1 milk. From the regulatory environment the position is supported by the DALRRD with the following pronouncement: “The Department is aware that there are local producers/manufacturers /retailers who are considering indicating the presence of the A2 protein or the absence of the A2 Protein (or both) in their milk/dairy products. However, in view of the current lack of South African based supporting scientific research around A2 type of beta-casein protein, the absence of a commercially available test and the legal status of the trade mark, the use of the above mentioned claims on dairy products regulated under regulation R 1510 dated 22 November 2019, will not be allowed in terms of regulation 32(3)(a) and (5)”.
EFSA, 2009. Review of the potential health impact of β casomorphins and related peptides. EFSA Scientific Report (2009) 231, 1-107. European Food Safety Authority, 2009.
Truswell, A.S., 2005. The A2 milk case: a critical review. European Journal of Clinical Nutrition 59, 623–631.