I will most likely sound like a broken record by the time we are done, if I don't already; taking nutrients into your body that you are unable to metabolize is a bad idea. Protease are "essential" for the proper metabolism of vitamin B12.
That is most likely why taking supplements of B12 are not effective. They can however, dramatically increase your risk of cancer according to studies. Cancer cells put out receptors to B12.

As I stated about the heme biosynthetic pathway:

"The first component in the heme pathway is succinyl-CoA. Vitamin
B12 serves as a cofactor for methylmalonyl-CoA mutase which converts
methylmalonyl-CoA to succinyl-CoA. Therefore, a lack of vitamin B12
would lead to a failure in the entire heme pathway."


How does this apply to MS and other autoimmune diseases? MS patients are unable to metabolize vitamin B12. Numerous studies confirm this. Here are the titles to a few. These studies particularly refer to the inability of MS patients to "metabolize" vitamin B12.

Multiple Sclerosis Associated with Vitamin B12 Deficiency
Reynolds, E.H., J.C. Linnell, J.E. Faludy. 1991. Arch Neurol. 48(8):808-11.

Vitamin B12 Metabolism in Multiple Sclerosis
Reynolds, E.H., T Bottiglieri, M. Laundy, R.F. Crellin, S.G. Kirker. 1992. Arch Neurol.

Vitamin B12 and its Relationship to Age of Onset of Multiple
Sclerosis
Sandyk, R., G.I. Awerbuch. 1993. Int J Neurosci. 71(1-4):93-9.