However, it should be brought out (and perhaps the article does this), the problem with B12 and older people is that the vitamin is absorbed in the stomach. But, many older people lose the intrinsic factor necessary for absorption. Therefore, a person can swallow as much B12 as they wish and still not get the vitamin into their system.
What is necessary are b12 injections and I contend at much higher levels than is recognized now.
While overseas, a medical person put my apparently unrelated symptoms together and developed a hypothesis that I may have pernicious anemia or perhaps a b12 deficiency. So, I began daily injections, the “loading” doses of b12. Within 2 or 3 days, I noticed a major decrease in my “fuzzy, fungus-in-the-brain” headaches and I wasn’t losing my balance as much as before. I increased the dosages and the headaches stopped. As I decreased the dose the headaches and dizziness began coming back.
That was about 1.5 years ago. I still need b12 although not quite as much as in the beginning. It does make a difference. I know this isn’t substantiated at this time by science but I’m experiencing it.
So how much do you take?
It's not absorbed by the stomach. B12 in the form of cobalamin first forms a complex with R binding protein in the stomach. Intrinsic factor is also released from the stomach. "As this protein is digested in the small intestine, cobalamin is transferred to intrinsic factor(IF). This complex passes through the intestine until it reaches specific receptors on the mucosa of the distal ileum." (Thats's the part of the small intestine right before you reach the large intestine, aka colon.) Italics are mine, ditto typos. That's part of the caption for Figure 107-2, P. 676, Harrison's Internal Medicine, 15th Edition copyright 2001. R binding protein is new to me too. Thanks for the opportunity to update my knowledge.
A dementia work up has included blood tests for syphilis, folate(the ionized form folic acid) and vitamin B12 for well over a decade, maybe two decades. They didn't say how they nailed the dementia as Alzheimer's. There's more than one, Pick's disease and vascular come to mind. You can have the neurologic symptons long before it shows up as pernicious anemia, IIRC.
Homocysteine and holotranscobalamin and the risk of Alzheimer disease