HEALTH FOOD INDUSTRY MYTHOLOGY: You Need the Truth About B12 Supplements.
RE: cyanocobalamin vs. methylcobalamin
The most biologically active form of vitamin B12 is neither cyanocobalamin nor methylcobalamin. The most active form of vitamin B12, and the form found in foods, is hydroxocobalamin. However, you will never find hydroxocobalamin in a nutrition supplement made by an honest company. The reason is that hydroxocobalamin is completely unstable when put in a tablet or capsule, and can only be taken by injection. Hydroxocobalamin is the form of vitamin B12 used for patients with pernicious anemia or other pathologies that need megadoses of vitamin B12 --- and it is only given by injection.
Cyanocobalamin vs. methylcobalamin makes an interesting comparison. Methylcobalamin is slightly more biologically active than cyanocobalamin, and is retained in the body slightly better. However, methylcobalamin is not well absorbed when taken orally, yet cyanocobalamin is. The very slight superiority of methylcobalamin over cyanocobalamin once it is in the body is completely negated by cyanocobalamin's superior absorption. The companies that put methylcobalamin in their supplements and make a big deal about it being a better quality than cyanocobalamin never tell you that all the studies showing its superiority were done by injected methylcobalamin, not oral methylcobalamin. To benefit from methylcobalamin taken orally, several thousand additional micrograms per day must be taken to equal the benefit of cyanocobalamin.
Cyanocobalamin is by definition vitamin B12. Methylcobalamin is not a "superior" vitamin B12, it is merely vitamin B12 with a methyl group attached. That molecule thus functions not only as vitamin B12 but as a methyl donor in transmethylation reactions. Methylcobalamin has become popular in the health food industry because as a methyl donor (not because of its vitamin B12 activity), it participates in the metabolism of homocysteine, one of the villains in cardiovascular disease. But, as stated above, the absorption of methylcobalamin is woefully inferior in comparison to cyanocobalamin.