A1- and A2-Milk and Their Effect on Human Health

Abstract

Milk proteins are a heterogeneous group of polymeric compounds that have a wide range of different molecular structures and properties. They occur as caseins, whey proteins, enzymes, minor proteins and nitrogen compounds. Caseins constitute about 80% of the total proteins of cow’s milk. β-casein is an important part of the caseins, which makes up about 37% of the total caseins. Within β-casein, there are a number of variants which are genetically determined. However, there are thirteen genetic variants of β-casein found in cow´s milk. A1 and A2 are the most common variants, which are called A1 β-casein (A1-milk) and A2 β-casein (A2-milk). The only difference between A1- and A2-milk is a difference in the 67th amino acid in the chain. At this position, A2-milk has a proline amino acid, while A1-milk has histidine amino acid. Several studies have reported that cow’s milk with a dominant or singular A2-milk may be healthier than A1-milk. These studies are based on digestion of A1-milk which lead to release β-casomorphin-7 (BCM-7). Subsequently increase inflammation, Type-1-diabetes, heart disease, autism, gastrointestinal discomfort and other disease in the consumer. For this reason, there is a growing global interest in A2-milk. In conclusion, the effects of A1-milk compared to A2-milk on human health show mixed results. On the basis of the available results, we cannot conclusively assess the health effects of A1-milk and A2-milk. Therefore, further investigations are needed.