I didn’t read any of the links and I’m no doctor or chemist, but here’s what I’ve learned (right or wrong) about B12, having been found deficient ten years ago.
As I recall, the liver does store a few years’ worth of B12, as someone mentioned above. To extract B12 from food (mostly found in animal products) is a very complex and delicate process. Stomach acid is necessary and that’s where I got into trouble because I was taking antacids long-term for acid reflux. It eliminated enough acid so that my digestive system couldn’t extract enough B12 from my diet.
What I’ve been doing for the past ten years is to take sublingual B12 tablets, as they are absorbed under the tongue directly into the bloodstream, by-passing the digestive system.
Some people think that “if some is good, more is better.” Not necessarily true, especially with vitamins or other essential nutrients. Being deficient in B12 can have horrible symptoms; it can mimic multiple sclerosis, among other things. Vitamin C deficiency (scurvy) can cause old mended bone fractures to break again, teeth can fall out, and you will eventually die. BUT, flooding your body with excess vitamins won’t give you “super health.”
Your body knows what it needs, and with water-soluble vitamins like B or C, the excess is flushed out in the urine. From what I understand, an excess of fat soluble vitamins CAN be toxic because they are stored in fat cells. Something like that. A few years ago my doc found I am also deficient in D, although there were no symptoms yet – so I take those also. Most of this is just because I’m old (68 next month) and things just don’t work as well as when we’re young.
In general, if you are not deficient in vitamins (blood test) it is pointless to take supplements.