Betsey Wingren wrote a question about B12 in the Vegetarian diet.

I have been a vegetarian, mostly Vegan  (no animal products) for several
years.  I slip up often enough to have gotten enough B12 as I
occasionally eat fish or lamb.  However,  a recent blood test showed I
was deficient in B12 and my doctor advised that I take a supplement.

I read that elderly people in general (I am 70)  have a tendency toward a
B12 deficiency which can cause a lot of problems for them; including
"Alzheimer-ish symptoms".  The article also noted that taking ordinary
supplement tablets wont work.  The B12 must be mixed with saliva in order
to get into our systems. My doctor said to "chew the tablet".  (not too
pleasant with the ordinary kind.)

Checked with the pharmacist, and sure enough, he had a B12 supplement
that comes as a little tablet that one puts under the tongue to dissolve.
It actually has a very pleasant flavor.  After a month I was re-tested
and my B12 is back up to normal, and I was told to cut down to taking the
B12 every other day.  I have to go back for another blood test in 2
months.

I am also "carbohydrate intolerant" which is just another name for the
early stages of Adult Onset Diabetes.  For that I take a daily tablet of
GTF (Glucose Tolerance Factor) Chromium and stick much more closely to my
Vegan diet, giving up desserts and exercising as often as possible.

Hope this information is helpful.                           Maggie