Hi guys
We’ve been really looking into the vitamin B12 source issue as there were some links that have made us question things. Here’s a summary.
The links reference studies where there’s been deficiency of vitamin B12, mainly citing references on deficiency in post gastrectomy or stomach cancer patients who do not have the ability of produce intrinsic factor (IF), a vital protein that combines with vitamin B12 for its absorption. Eg http://www.ncbi.nlm.nih.gov/pubmed/21556950 - these people had vitamin B 12 malabsorption.
Adams JF, Ross SK, Mervyn L, Boddy K, King P. Absorption of cyanocobalamin, coenzyme B 12 , methylcobalamin, and hydroxocobalamin at different dose levels. Scand J Gastroenterol. 1971;6(3):249-52 - Found that all forms of B12 were absorbed at the same rate and they claimed that methylcobalamin with IF was efficient, while cyanocobalamin is better absorbed by passive diffusion.
Okuda K, Yashima K, Kitazaki T, Takara I. Intestinal absorption and concurrent chemical changes of methylcobalamin. J Lab Clin Med. 1973 Apr;81(4):557-67 - Suggest that once absorbed, methylcobalamin may be better retained than cyanocobalamin.
The links that claim megadoses of methylcobalamin are needed also claim that megadoses of other forms, including cyanocobalamin, are useful, which limits their credibility.
One point in: http://veganhealth.org/b12/noncyanob12 is where they say:
Currently, we do not have sufficient evidence to suggest that the benefits of using MeCbl or AdoCbl override that of using CNCbl or HOCbl in terms of bioavailability, biochemical effects, or clinical efficacy. There is uncertainty regarding the claimed superior role of [B12] coenzyme forms for prevention and treatment of [B12] deficiency. However, HOCbl may be an advantageous precursor of the cofactors, particularly in the inherited disorders of metabolic Cbl processing. CNCbl is a more stable and inexpensive form that appears to be best suited for oral supplementation and parenteral [intravenous] treatment as well.
Sure we might not have evidence to support the fact that MeCbl is better, but we do know that it’s preferentially tolerated. Also, CNCbl is not natural and the other forms are. Also, we do not consume megadoses from food. Even in a meat, egg and animal product-rich diet with large intakes of these foods, at most you’ll be consuming 30-50 mcg of vitamin B12 per day a lot less than the 1,000 + mcg claimed.
The other issue raised was the concern that the other bioactive form, adenosylcobalamine can be converted from MeCbl metabolism requires this form for different processes. This is a very valid concern as described in this report: http://www.ncbi.nlm.nih.gov/pubmed/25117994 and other links that question this point centre around that report. However, that report, again, was based on treating vitamin B12 deficiency not in well people. If you look at vitamin b12 metabolism, hydroxycobalamin, the most common form found in food, when it enters the cell, loses its hydroxyl part and becomes free cobalamin before the addition of a methyl or adenosyl group making the methylcobalamin or adenosylcobalamin molecule respectively. When methylcobalamin is being used as a co-factor for homocysteine metabolism, it loses its methyl group, making it free cobalamin; i.e. there is free cobalamin available for the adenosyl group top make adenosyl metabolism. This is demonstrated by this study: http://www.ncbi.nlm.nih.gov/pubmed/7241237
However, we accept that this is in vitro and, although this provides a very credible explanation due to there being conflicting evidence, we are adding cyanocobalamin back into the formula in the short term until we have looked into this issue more. The added cyanocobalamin will be on top of the methylcobalamin.
I will continue to update you.
