There are four types of vitamin B12, none are naturally found in vegan food, but all are available as vegan supplements.
Cyanocobalamin and hydroxocobalamin are two types which have to be converted into active forms of B12 before our bodies can use them. These forms are not required by the body if active B12 is used instead. Hydroxocobalamin isn’t normally available in vegan products but is available via injections which may be vegan. Cyanocobalamin is an articificial form that isn’t found in nature, but is found in all B12 fortified foods and most supplements (including The Vegan Society supplement). When B12 was first discovered, contamination with cyanide from charcoal during its extraction from animal tissues led to this discovery producing cyanocobalamin, rather than the active forms of B12, and this form is still widely used. Cyanocobalamin is a far from ideal form for supplementation because:
- It can take up to 2 months for our bodies to convert it into usable forms
- It can’t be stored in the body for as long as active forms of B12
- Its conversion involves the release of a cyanide molecule, which then has to be removed by glutathione in the body. Glutathione synthesis is dependent on the methylation cycle working properly (which requires good levels of active B12), so the body would be unable to convert cyanocobalamin to usable B12, when a person is B12 deficient
- Some organisations advise smokers not to take it because smoking also releases cyanide into the body
- Some people are unable to convert non-active B12 into active B12
- The NHS and others advise pregnant women not to take it
All of the above points, except those on cyanide, are also applicable to hydroxocobalamin. Some vegans have taken cyanocobalamin for a long time without any issues, so for them this form is probably fine. When the above is considered however, it seems possible that even these people could get on better with active B12 (see below), and we wouldn’t advise the use of cyanocobalamin for people just starting out with supplements.
Methylcobalamin and adenosylcobalamin (also known as dibencozide) are the other 2 forms of B12. Methylcobalamin and adenosylcobalamin are never added to food, though naturally sourced vegan versions (from bacteria) are available. These are active forms of B12, so if absorbed, these types of B12 can be used by the body straight away. The body needs both of these types of B12. Methylcobalamin is used to breakdown homocysteine in the methylation cycle and adenosylcobalamin is used to breakdown methylmalonic acid (MMA) in the Krebs cycle. If only one active form is available, the body normally converts some of the form it has into the other, to have both. Some people cannot convert methylcobalamin into adenosylcobalamin, so it is sometimes necessary to supplement with both in order to recover from or avoid a deficiency.
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