This is a very interesting blog from Science Based Medicine discussing B12 deficiencies and supplementation. B12 has come up on this forum a number of times (including as an ingredient in Magic Milo! 
) so I thought it may be of interest:
Interesting article. I have had B12 injections every 3 months for the last 10 years, I was below the reference range when tested on the NHS, even with the B12 shots my blood levels dont go high. I have no problem with intrinsic factor (they tested everything) including giving me the schilling test, I am not veggie and love red meat, especially good for the blood sugar.
They couldnt find a reason that I am low on B12. The injections make me feel rotton for a week, but then I think they do help but nothing that I could say I notice, I just know when I am late for my injection I seem to go downhill, so they do a little, but not a lot.
Christine
— Begin quote from “cmoc”
Interesting article. I have had B12 injections every 3 months for the last 10 years, I was below the reference range when tested on the NHS, even with the B12 shots my blood levels dont go high. I have no problem with intrinsic factor (they tested everything) including giving me the schilling test, I am not veggie and love red meat, especially good for the blood sugar.
They couldnt find a reason that I am low on B12. The injections make me feel rotton for a week, but then I think they do help but nothing that I could say I notice, I just know when I am late for my injection I seem to go downhill, so they do a little, but not a lot.
Christine
— End quote
I take 500 microgram of B12 daily which is several hundred times more than the RDA. Although I have taken this dose for over a year my blood tests show B12 levels somewhere between middling to high. I expected I would be at the top end of the normal scale if not well beyond it!
I haven’t had a test for intrinsic factor and I’m not planning to as my B12 levels seem adequate. The wonder is that the B12 level is not really high.
-Wexan
That’s a really good article Vic.
There is a huge industry making tons of money out of people’s worries and concerns, when there is very little scientific evidence to support taking vitamins unless you have a medical reason to do so (e.g. malabsorption caused by pernicious anaemia, or by certain drugs), or have a very restricted diet.
And as an aside, it’s usually much better to take in vitamins through diet rather than as a supplement, as often they are not as well absorbed when in non-dietary forms.
Beachleaf, I share your bias in favor of dietary intake rather than popping pills. OTOH, when they discovered I had bone loss–and I realized I’d loss two inches–they started me on chalk pills, and told me that high dietary calcium didn’t necessarily get absorbed as well, even if I ate the same amount of Vitamin D as the CaCO3 pills contain.