Vitamin B12, also known as cobalamin, is an important water-soluble B vitamin involved in red blood cell production, and neurological health. A deficiency in this key vitamin can cause serious symptoms. Therefore, many people turn to vitamin B12 supplements to help meet their needs and prevent a deficiency.
Vitamin B12 supplements are typically derived from two sources : cyanocobalamin or methylcobalamin. Both are nearly identical and contain a cobalt ion surrounded by a corrin ring. However, each have a different molecule attached to the cobalt ion. While methylcobalamin contains a methyl group, cyanocobalamin contains a cyanide molecule.
Cyanocobalamin is a synthetic form of vitamin B12 that is not found in nature. It’s used more frequently in supplements, as it’s considered more stable and cheaper than other forms of vitamin B12.
When cyanocobalamin enters your body, it’s converted into either methylcobalamin or adenosylcobalamin in three distinct steps. This reaction is partly dependent on other vitamins and coenzymes and uses up the body’s resources; a clear disadvantage. Part of the cyanocobalamin obtains its methyl group from SAM, through which the latter is broken down and can no longer fulfill its aforementioned tasks. However, vitamin B12 is actually responsible for the formation of SAM.
Unlike cyanocobalamin, methylcobalamin is a naturally occurring form of vitamin B12. A study comparing the two forms reported that about three times as much cyanocobalamin was excreted through urine, indicating that methylcobalamin may be retained better within your body. Methylcobalamin is significantly better absorbed into the cells than cyanocobalamin. Although B12 blood values initially rise higher with cyanocobalamin than with methylcobalamin, shortly thereafter a large portion of the cyanocobalamin is excreted, whereas methylcobalamin reliably increases the vital cellular B12 level (1).
In light of these factors, natural, bioactive methylcobalamin proves to be a much better choice of active ingredient in vitamin B12 supplements than the synthetic cyanocobalamin. (2) (3) (4).
References：
(1). 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. PubMed PMID: 4696188.
(2). Kelly G. The co-enzyme forms of vitamin B12: Toward an understanding of their therapeutic potential. Alt Med Rev. 1997;2(6):459-471.
(3). Tsao C, S, Myashita K, Influence of Cobalamin on the Survival of Mice Bearing Ascites Tumor. Pathobiology 1993; 61:104-108.
(4).Tetsuya Watanabe, Ryuji Kaji, Nobuyuki Oka, William Bara, Jun Kimura, Ultra-high dose methylcobalamin promotes nerve regeneration in experimental acrylamide neuropathy, Journal of the Neurological Sciences, Volume 122, Issue 2, April 1994, Pages 140-143, ISSN 0022-510X.
