Which B12 supplement should I take?
Recently I have been asked about vitamin B12 a lot: Which is the best B12 supplement? Do I need to take B12 now that I follow a vegan diet? What is the difference between cyanocobalamin, hydroxycobalamin and methylcobalamin?
Whole books had been written on the fascinating and complex subject of B12 but here I offer an overview of some of the key points .
What is vitamin B12?
Vitamin B12 (also known as cobalamin) is an essential vitamin. ‘Essential’ means your body cannot make its own B12 and therefore must obtain it through food.
It is a water-soluble vitamin like vitamins B1, B2, B3, B5, B6, folate and vitamin C, but it differs from the other water-soluble vitamins in that:
It is synthesised by bacteria and becomes incorporated upon ingestion in animal tissue; therefore the only sources of vitamin B12 are foods of animal origin. Foods of non-animal origin contain no B12 (they have no need for B12 as they do not contain cobalamin-dependent enzymes) unless they are fortified or contaminated by bacteria.
B12 is stored in the liver for about 4 years. Most water-soluble vitamins are rapidly lost from the body, partly because the water in cells dissolves these vitamins and they get excreted via the kidneys, but vitamins B6 and B12 are exceptions to this.
In the blood, B12 is transported bound to proteins, such as Transcobalamin and Haptocorrin.
Its absorption is unique: it requires a compound called intrinsic factor to be absorbed once eaten.
It has a very complex structure that contains cobalt, hence the name cobalamin.
The Functions of B12
Vitamin B12 has many functions
It is involved in the formation of red blood cells
B12 is needed to convert folate to its active forms
Energy metabolism
Nervous system: Plays a role in the formation of myelin sheath, which provides insulation around specific parts of most neurons.
Immune system: B12 is a key factor in the synthesis, development and activity of immune cells
It is needed to make new cells
Together with vitamin B6 and folate, B12 is needed to metabolise homocysteine, an amino acid which has been linked to an increased risk of heart diseases when present in high concentrations.
Types of B12
The type of vitamin B12 depends on the group attached to the cobalt that sits at the centre of this complex vitamin. There are four main types of vitamin B12:
Cyanocobalamin
Hydroxycobalamin
Adenosylcobalamin
Methylcobalamin
Hydroxycobalamin, methylcobalamin and adenosylcobalamin can be found naturally in foods. Cyanocobalamin is the synthetic form of B12. B12 supplements will contain one or more of these forms.
1. Cyanocobalamin
This is the cheapest form to produce and so is the form you will find in cheaper supplements. Due to its stability it is commonly used in pharmaceutical preparations.
This was the first form in which B12 was isolated. It does not occur naturally, but it is rather an artefact caused by the presence of cyanide in the charcoal used in the extraction procedure. It was a long, hard process to successfully isolate B12 for the first time. It was achieved in 1948 when researchers of B12 passed their concentrates through a charcoal column. The cyanide in the charcoal replaced the unstable metabolically active groups attached to the cobalt, resulting in the stable (but vitamin-inactive) cyanocobalamin.
Once ingested, cyanocobalamin has to be converted to an ‘active form’ before it can be utilized by the body. If it is not converted, cyanocobalamin may have antivitamin action, which means it can block the action of the active forms of B12. Cyanocobalamin supplementation has also been implicated in the neurological damage associated with cyanide intoxication, but this is very rare. Due to the cyanide component there are also concerns regarding supplementation of cyanocobalamin in smokers as they may already have an excess of thiocyanate in their blood.
2. Hydroxycobalamin
This is the form that is prescribed by GPs to manage B12 deficiency and is usually administered as an injection. It is also used to minimize cyanide poisoning.
Once ingested from foods or supplements, Hydroxycobalamin needs to be converted into the active forms, methylcobalamin and adenosylcobalamin, in order to be used by the body.
Cobalamins are transported in blood bound to proteins. Hydroxycobalamin has the highest affinity to plasma proteins so stays bound to them longer and is eliminated, via the kidneys, slower than other forms of B12.
3. Adenosylcobalamin
Adenosylcobalamin and methylcobalamin are the two active forms of B12, meaning that unlike cyanocobalamin and hydroxycobalamin they do not have to be converted by the body in order to be utilised.
Adenosylcobalamin is stored in the mitochondria and it is the primary storage form of B12.
It plays a role in the metabolism of carbohydrates, fat and amino acids and is involved in the formation of myelin sheath which surrounds the axon of nerve cells; thus is needed for the proper functioning of the nervous system.
4. Methylcobalamin
An active form of B12, this is found in the cytosol of cells and is the predominant form found in blood.
It is primarily involved along with folate in the formation of red blood cells and in the methylation of homocysteine to methionine, which is important for DNA and protein synthesis. If homocysteine is not recycled to methionine or converted to cysteine, then homocysteine levels build up which can then damage blood vessel linings and cause inflammation.
In recent years, methylcobalamin has been extensively used and promoted as being the preferred choice of B12 supplementation. Methylcobalamin can be taken orally or given as an injection. However, the methylcobalamin injection is unstable and can be expensive.
Should Vegans take B12?
As mentioned above, only foods of animal origin are good natural sources of vitamin B12. As such, vegans may develop a B12 deficiency over time. If you have just started a vegan diet you don’t need to supplement with B12 straight away (unless you were already deficient) but it’s worth ensuring you get a source of B12 in your diet from two years onward to avoid deficiency. Some vegan foods are fortified with B12, and other vitamins and minerals, to make this easier.
Is B12 easily absorbed?
Digestion, as with almost every other aspect of this vitamin, is a complex business. Uniquely, to be absorbed from the gut into the bloodstream B12 requires a compound called intrinsic factor to be present in the gut. Intrinsic factor is released from the cells of the stomach. Adequate stomach acid levels and good digestion are also needed to release B12 from the protein to which it is bound in the food state. The likelihood of having problems absorbing B12, along with the likelihood of a deficiency of B12, is increased in the elderly. Having a deficiency of intrinsic factor or being on medication that suppresses stomach acid production (such as proton pump inhibitors like Omeprazole) may mean that B12 supplementation in the form of injections is the most suitable option in some cases of B12 deficiency.
Key Takeaway…So which B12 supplement should I take?
This is definitely worthy of further debate, but for oral supplementation methylcobalamin is generally the preferred choice. However, it is certainly worth considering a supplement that contains a combination of both methylcobalamin and adenosylcobalamin, since they have distinct metabolic functions.
B12 supplements containing methylcobalamin are usually more expensive than B12 supplements that use cyanocobalamin or hydroxycobalamin. The label of any reputable supplement should tell you which forms of B12 are in the product.
