Please read -
https://en.wikipedia.org/wiki/A2_milk
in which it says -
Health effects
The European Food Safety Authority (EFSA) reviewed the scientific literature and published their results in 2009. As part of their evaluation, the EFSA looked at the laboratory studies that had been done on
BCM-7 where they had found that BCM-7 can act as a weak
opioid receptor agonist.
[2] The EFSA found no relationship between chronic diseases and drinking milk with the A1 protein.
[2] In most of the animal studies, BCM-7 was not administered orally, as humans would be exposed to it, but rather was given to animals by injection
into the peritoneal cavity or even directly
into the spinal cord or brain, which makes these studies not useful for understanding how BCM-7 might affect humans.
[2] The EFSA study emphasized
the dangers of drawing conclusions from correlations identified in epidemiological studies and
the dangers of not reviewing all the evidence at hand.
[2] Another 2009 review found no demonstration that consuming milk with A1 casein causes diabetes.
[4] A 2014 review of research into the relationship between consumption of dairy products (including A1 and A2 proteins) and the incidence of diabetes found that while there appears to be a positive correlation between consumption of dairy products by babies and the incidence of type 1 diabetes (T1D), and an inverse relationship between the consumption of dairy products and the development of type 2 diabetes (T2D), these correlations are tentative; it is impossible to determine what component or components of milk might be responsible for these effects, and it is unlikely that the expensive and complex research to determine the answers to these questions will ever be conducted.
[5]
Milk with predominantly A2 protein is not a milk substitute for infants with cow milk protein allergies.
[6]
The a2 Milk Company claims that people who experience discomfort drinking ordinary cows' milk may experience relief when they switch to milk with predominantly A2 protein.
[7][8][9]
(20min delay)