Background：There are several genetically-determined variants of β-casein, the protein which constitutes about 25-30% of cows』 milk proteins. One variant, A1 β- casein, has been implicated as a potential etiological factor in type 1 diabetes mellitus (DM-1), ischaemic heart disease (IHD), schizophrenia, and autism.

Another variant (A2 β-casein) has not been implicated in these diseases. It is known that nutrition in early life has important health consequences in both childhood and adulthood. Cows』 milk is a basic food for most infants and children and a common food for adults in most western societies. Therefore, if some components of milk are causative or protective of the diseases mentioned, it would have major public health implications.

The evidence to support the hypothesis that the A1/A2 composition of milk is an etiological factor in these diseases is reviewed.