Which vitamin B12 is best absorbed?

Many people take extra vitamin B12, especially vegetarians and vegans, because vitamin B12 naturally occurs mainly in animal products. If you take vitamin B12, it may be helpful to know which forms exist and which are more readily absorbed.

Vitamin B12 supplements

B12 with cyanocobalamin

Most B12 supplements contain cyanocobalamin. This form does not naturally occur in living organisms, but it has the advantage of being very stable. However, that stability comes with a downside. In order to use it, the body must first remove the cyano group, and then the cobalamin must be converted into the active forms of vitamin B12: methylcobalamin and adenosylcobalamin. The extent to which this conversion takes place can vary from person to person. Reduced stomach acid, for example, decreases the effectiveness of intrinsic factor and therefore the conversion of B12.

Active vitamin B12

There are clear indications that taking an active vitamin B12, such as methylcobalamin or adenosylcobalamin, is preferable to taking cyanocobalamin when B12 conversion is impaired. Methylcobalamin is retained by tissues better than cyanocobalamin. Methylcobalamin and adenosylcobalamin are forms of vitamin B12 that occur directly in the body. Methylcobalamin is mainly present in the cytoplasm of a cell, where it functions as a methyl-group donor. It contributes to the remethylation of homocysteine to methionine and, together with folate and vitamin B6, supports healthy homocysteine metabolism. Adenosylcobalamin is found in the mitochondria, where it acts as a cofactor in the conversion of methylmalonyl-CoA to succinyl-CoA—important for the metabolism of fatty acids and proteins and for energy production. Among other things, these forms differ in structure and in how they are used in the body.

Author: Sanne van der Rijt