I just checked the vitamins that I take on a daily basis. They include 125mcg of B12 and state that this is 5000% of the recommended dose. Now getting a 2000mcg dose is then much higher than what doctors recommend.
Your gut will not be able to absorb anywhere near 125 mcg of B12. When you take that dose, you are probably only absorbing a few mg. This is because oral vitamin B12 can only be absorbed with the help of
intrinsic factor, which is secreted by cells in the stomach. But very little intrinsic factor is produced.
If you take a 1 mcg oral dose of B12, 56% of that will be absorbed with the aid of intrinsic factor; but as you increase the dosage, B12 absorption dramatically decreases because with higher doses the very limited capacity of intrinsic factor is exceeded. Ref:
here.
This is why if you want very high B12 doses, you have to look at other routes of administration such as B12 injections or B12 transdermal oils, or possibly B12 e-cigarettes.
But still you get a positive effect from it. What do you guys think is the mechanic behind this? Is this flooding of Vit B12 forcing the cells to take some of it up when otherwise they would reject it (due to sickness)?
Nobody knows for sure why high doses of B12 help ME/CFS. Part of the problem is that we do not know what causes ME/CFS and its symptoms such as brain fog in the first place.
But generally speaking, the effect of any supplement or drug is often proportional to its dose, and vitamins are no exception. The various physiological effects that a vitamin has in the body do not become saturated once you reach the dose that prevents deficiency; doses beyond that which prevents deficiency thus have further effects.
Ultra-high dose methylcobalamin
has been shown to promote nerve regeneration, and
shown to protect against glutamate-induced neurotoxicity. And high dose methylcobalamin is
known to boost natural killer cell and CD8 cell immunity. However, whether any of those mechanisms can explain the benefits of high dose B12 for ME/CFS is anyone's guess.
Dr Sarah Myhill has a page on the
rationale for using vitamin B12 in CFS, but reading it does not leave us much wiser in terms of pinpointing the mechanism of action.
Prof Carl-Gerhard Gottfries observed in a
study that an injection of 1 mg of vitamin B12 given every 4 days plus folic acid 7 mg daily helps ME/CFS. Gottfries found methylcobalamin injections give better results than hydroxocobalamin.