B12 is a group of cobalt-containing vitamins. Hydroxocobalamin and cyanocobalamin are synthetic forms of vitamin B12. The two forms of vitamin B12 naturally occurring in foods are methylcobalamin and adenosylcobalamin. These forms are biologically equivalent.
B12 is produced by a number of different species of bacteria which is found in the soil, on the surface of some plants and some red and green algae.
Lack of vitamin B12 can have serious consequences as does high levels of homocysteine. Determining the status of vitamin B12 and homocysteine can be difficult and can be determined by measuring serum vitamin B12, homocysteine and methylmalonic acid (MMA).
A number of products contain riboflavin, pyridoxine, folate, B12 and methionine way in excess of dietary requirements in an attempt to resolve B12 metabolism problems.
Many magnesium supplements contain pyridoxine which is usually unnecessary and possibly detrimental.