Though the reference ranges in the US start around 200 as a minimum acceptable level, most of us here--and most o ther first world countries--think that figure is much too low. In Japan and most parts of Europe, the reference range starts at 500-550. Many of us would consider a range in the 700's (depending on whether supplements have been taken recently) to be a more acceptable minimum--and many of us here keep our levels well into four figures if we can.

Since B12 cannot hurt you, and it is cheap to use, you could do worse than to start on a 1000mcg dose daily--more if you like. An amount that large allows a decent amount of passive absorption even if you are malabsorbing from food due to stomach or other issues, so long as you take it apart from food or other supplements and meds (I'd say at least an hour window either way).

If you can, see if you can get methylcobalamin rather than the more common cyanocobalamin--the former has to go through far fewer metabolic hoops to be used (and who wants cyanide radicals that have to be eliminated from the body anyway?). One can get these in sublingual form--they can be held under the tongue and dissolve slowly.