A2 Milk: The Impact of Genetic Variation in Milk Protein on Human Health

Recently, a new type of cow's milk has been commercialized in the markets, called A2 milk. It is derived from a specific allelic composition on chromosome 6. The only difference between A1 and A2 milk results from the polymorphism at the 67 amino acid chain. In this position, A2 milk has a proline amino acid, while A1 milk has a histidine amino acid. Proteins are one of the most important components of milk, especially casein, and have received significant attention as they are the source of bioactive opioid peptides called beta-casomorphin-7. Peptides are released through enzymatic digestion of casein and whey proteins. More precisely, this bioactive peptide is produced by sequential gastrointestinal digestion of bovine A1 variants proteins, while this phenomenon is not present in variant A2. Studies have reported that A1 milk can be harmful to health not only for adults but also for infants and that β-casein A2 becomes a safer choice following the relationship between disease risk and consumption of the beta-casomorphin-7 peptide. Indeed, epidemiological studies suggest that the released beta-casomorphin-7 peptide is a risk factor for the development of diseases in humans, but this has not yet been validated by other studies. In contrast, A2 milk has been suggested as an appropriate substitute for A1 milk since populations consuming milk containing high levels of the A2 beta-casein variant have lower rates of diseases, such as diabetes, coronary heart disease, autism, and schizophrenia.