Can the (excessive) consumption of milk negatively affect autoimmune diseases such as Multiple Sclerosis? In internet forums, it’s not uncommon for people affected to report problems after consuming dairy products, sometimes even a worsening of their symptoms. In contrast, the image of milk in advertising remains largely positive. In fact, since the late 1970s, a connection between milk and MS has been considered. In the nineties, a correlation between milk consumption and MS was proven, especially for the consumption of pure cow’s milk. This context is important when considering the new study from the working group led by Stefanie Kürten (Chunder R et al. Antibody cross-reactivity between casein and myelin-associated glycoprotein results in central nervous system demyelination. Proc Natl Acad Sci U S A. 2022 Mar 8;119(10):e2117034119. doi: 10.1073/pnas.2117034119. Epub 2022 Mar 2).
What was done?
The researchers injected different milk proteins into mice. Mice that were injected with casein showed a range of (mild) neurological symptoms. After injecting other milk proteins, these symptoms were not observed. Under an electron microscope, the nerves of these casein-immunized mice showed clear changes to the myelin sheath. This is the covering structure of nerve cells, which is also the primary target of immune cells in MS. Interestingly, the researchers could not find any immune cells in the altered nerves. This suggested that antibodies (which were formed against the milk protein casein) are responsible for the damage to the myelin sheath.
This finding suggested that the injection of casein led to a misguided immune reaction. Because the antibodies, which should have fended off the (foreign protein) casein, caused damage to the myelin sheath. Therefore, the researchers next examined whether there is cross-reactivity between casein and protein molecules of the myelin sheath. Such cross-reactivity can occur when two protein molecules are very structurally similar. Then there is a risk that the immune system confuses the two proteins.
Similarity between Casein and MAG
In fact, it could be shown that casein has a great similarity to the so-called myelin-associated glycoprotein (MAG). The serum from mice immunized with casein was able to recognize MAG on brain and spinal cord slices. Therefore, there is a reasonable suspicion that in the casein-treated mice, the body’s own defense also targets MAG, thereby destabilizing the animals’ myelin.
To clarify the question to what extent these results from the animal model can be transferred to humans, the researchers supplemented the results obtained from the mouse model with clinical data. Here it was shown that serum samples from patients with MS showed a significantly higher B-cell and antibody reactivity to casein than those from patients with other neurological diseases.
How should observations and study results be interpreted?
How can we bring together and interpret the observations of people affected by MS, that milk consumption leads to a worsening of symptoms, and the results of the Bonn working group? It is conceivable that the individuals developed an “allergy” to casein through the consumption of milk. When they consume fresh milk products, casein antibodies are formed, which, due to the cross-reactivity with MAG, damage the myelin layer around the nerve fibers.
Therefore, the Bonn working group is currently developing a self-test with which affected individuals can check whether they carry corresponding antibodies. In light of the current findings, this group of MS patients should avoid milk consumption. It is also of interest whether cow’s milk also increases the risk of developing MS in healthy individuals. Because even in healthy individuals, an immunological reaction to casein can be induced and theoretically cross-reactivity against MAG can occur. However, additional factors are needed to then trigger an autoimmune disease like MS.
The results on milk and autoimmunity are interesting and should lead us to reconsider our milk consumption in adulthood – also because of the climate.
