Effects of A1 and A2 variants of β-casein on human health—is β-casomorphin-7 really a harmful peptide in cow milk?

This article aims to review the effects of cow milk containing A1 or A2 or mixed variants of β-casein on human health. The information based on the health effects of cow milk was collected from the most authentic scientific database including Scopus, PubMed, and Google Scholar by searching specific keywords like “cow milk”, “A1A2 beta-casein”, “beta-casomorphins”, “A2 cow milk”, and “A2 milk”. The search hits a total of 197 articles including patents in which about 70 most relevant articles were critically reviewed. The literature revealed that the most abundant category of cow milk found worldwide is mixed A1/A2 in which both A1 and A2 variants of β-casein are found in equal ratio. Among the major three categories, A2 cow milk received much attention both from the scientific community and the wider public due to its possible health benefits over A1 milk mainly in diabetes and heart-related problems. On the other hand, milk containing the A1 variant of β-casein is supposed to be harmful due to the formation of β-casomorphin-7 (BCM-7) peptide, although the scientific community is not unanimous for this claim. The claim for the harmful effects of the A1 variant should be further validated with more scientific studies.