It's amazing how much impact a single vitamin can have, but that's why they are called Vitamins!
Dr Joe Chandy has been a GP in Easington in County Durham, UK for 40 years. I recently attended a presentation about the impact on the body systems of subclinical B12 levels in the tissue - not recognised by medical science because the blood levels were above the minimum required.
Dr Joe pointed out that the criteria for diagnosing B12 deficiency have been moving ever since he began highlighting the problem, from 150ng/ml to 200, from "it's not possible in pregnant women and children" to "they may need treatment too" and he highlights how easy it is to spot the symptoms (neuropathy, depression, various body effects) but how difficult to confirm deficiency in the lab with our current tests.
Of course the easiest test is to offer B12 supplements (low cost, few if any side effects) and see if the symptoms go away, but that seems to be too simple for modern doctors.
there's a B12 deficiency support group on www.b12d.org. The powerpoint presentation is 21MB and won't download in a hurry; we're planning to examine the themes and publish these it but it will take time. Please add comments.