In response to:  "How is the mom taking the vitamin?   If it is orally, most of it will not be
absorbed.   I believe a sublingual form will have better absorption and an
injection the best of all.   My understanding is that there is no harm with
taking large doses of B-12. Aloha, Gloria Thai" Arly replies:  B12 (cyanocobalamin) is absorbed well by the normal route (swallowing) by anyone who produces intrinsic factor in the gastric mucosa.  Intrinsic factor is something the body makes which enables the B12 to enter the bloodstream. This is the normal state of health for most of us; however, there are some diseases which interfere with either production of instrinsic factor or one of the other few steps of digestion and absorption of B12.  These are more prevalent in the elderly but fairly uncommon in women of breastfeeding age. Clearly, anyone receiving an injection is bypassing this route of absorption and the B12 enters the bloodstream directly.  There is a general concern with pharmacological doses (megadoses) of the B vitamins, as there are for other vitamins and minerals.  It took many people presenting with irreversible nerve damage from megadoses of B6 for us to recognize 20 years ago that it was quite possible to overdose on vitamin B6 (pyridoxine).  It is probably possible to cause damage from severe overloads of any vitamin B; what would consititute an overdose would vary between individuals.  At this point hypervitaminosis B12 (the disease caused by too much B12) is quite rare, and seems to be reversible by discontinuing the huge doses.  As people experiment on themselves with increasing dosages, we may discover hypervitaminosis toxicity which we would not see in nature, and we may find a point at which the damage is not so easily reversed.  Mostly anecdotal reports exist suggesting reversible symptoms of diarrhea, cutaneous rash, polycythemia and possibly peripheral vascular thrombosis.  We do know that B12 is very efficiently stored in the body for at least two years after consuming B12 ceases. Cyanocobalamin contains a structure which is similar to a structure in blood; it also contains cobalt and cyanide. It is involved with growth, and the nervous system and blood system in particular. Some people might be sensitive to megadoses that other people would be impervious to.  The safety mechanism here is that by swallowing the vitamin, instead of injecting it, theoretically any amount which was not matched by the body's own instrinsic factor should be just wasted and go through the intestinal tract unabsorbed, creating expensive fecal waste but no harm.  This is just an off-the-cuff hypothesis, and may not reflect what actually happens, since megadoses in general act as drugs as well as nutrients.  In summary, I found two citations for hypervitaminosis B12 on PubMed; one seemed to suggest acne as one possible sequelae.  Here is the abstract for the other:   Hypervitaminosis B12 in maintenance hemodialysis patients receiving massive supplementation of vitamin B12.  Mangiarotti G, et al. Int J Artif Organs. 1986 Nov;9(6):417-20.

"We have administered routinely a multivitamin preparation containing a megadose of B12 to 106 hemodialysis patients after dialysis treatments. We found that these patients had very high levels of serum vitamin B12 which returned to original values only after a period of three years after stopping the vitamin.*It is not known whether maintaining a prolonged high level of vitamin B12 is harmful. However, animal and epidemiologic studies have suggested that both cobalamin and cobalt may be potentially toxic. In view of the absence of demonstrable benefit and the possible risk of toxicity, we believe that the use of such megadose vitamin compounds in dialysis patients should be re-evaluated."  Yours, Arly Helm, MS, Nutrition and Food Sciences; IBCLC

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