See Vitamin B12: Your Guide to Benefits, Deficiencies and Supplementation – CNET
Notes that B-12 deficiency is of concern to older adults, vegans and vegetarians, those with some medical conditions such as celiac disease, and those on some medications that can impact the absorption. Even taking vitamin C can affect B-12 absorption.
The article quotes the recommended daily requirement of 2.4 mcgs of B-12. This can be misleading as that is how much you need to absorb – at my doctor’s direction, I take 1,000 mcg per day – and probably absorb 10-13 mcg of that. The 2.4 mcg was set in 1958; other countries recommend higher daily amounts.
