--taken over a long period of time, do impact the absoprtion of a number of vitamins and minerals, B12 prominent among them, as the reduced acid production makes it much more difficult to break these nutrients out of food by the usual chemical digestion process.

It is a good idea to take the methylcobalamin B12--the megadosing, 1000-5000mcg/day is designed so that 1-2%, enough for daily requirements and perhaps a bit more, will be passively absorbed, bypassing the usual stomach route--but it's best to take it on an empty stomach, well apart from anything else, as the cobalamin molecule is the largest the body regularly uses and it is very to interfere with its absorption--any fiber or food will interfere with best absorption, as will a lot of medications.