Several types of B12 exist, the important question to keep in mind is, are you getting sufficient amounts of the right kind of B12?
What Are the Four Types of Vitamin B12?
Vitamin B12 also known as cobalamin, and comprises a number of forms including cyano-, methyl-, deoxyadenosyl- and hydroxy-cobalamin.
- Cyanocobalamin is a synthetic compound formed in the lab, used in many nutritional supplements and injectables involving vitamin B12 preparation. It is usually found at most in trace amounts in human plasma, although people exposed to cigarette smoke (which contains cyanide) often have higher plasma cyanocobalamin levels. Cyanocobalamin must be converted to other cobalamins to become active, so this form is not the best type of B12 to ingest via supplementation or intramuscularly.
- Methylcobalamin and 5-deoxyadenosylcobalamin (also known as adenosyl-cobalamin) are the coenzyme forms of vitamin B12 that play a role in human metabolism. Methylcobalamin is the most readily absorbable form of vitamin B12. It is also most bioavailable because your body requires little effort to convert to the stable form since methylcobalamin already acquires methyl group. Hence, methylation is an important process, in which your body utilizes the methyl groups to stabilize free radicals and remove toxins. This essential step protects your brain from degeneration by decreasing the glutamate, a non-essential protein that causes neural damage.
- Hydroxycobalamin is also found in the human body; it is a stable form of vitamin B12 that can be converted to active coenzyme forms. Hydroxycobalamin is given intravenously or intramuscularly for vitamin B12 deficiency and for the treatment of cyanide poisoning.
- Adenosylcobalamin is the least stable form outside of the body and is not the best choice for oral supplementation.
What Are the Signs and Symptoms of Vitamin B12 Deficiency?
The neurological manifestations of vitamin B12 deficiency may become irreversible if not treated in a timely manner.
The long-term consequences of sub-clinical deficiency may include the following:
- Chronic fatigue
- Low energy
- Loss of memory
- Numbness and tingling in hands and feet
- Permanent nerve and brain damage
- Inability to maintain balance
- Tremors in adults
- Infants: feeding difficulties, irritation, slow growth, and tremors
- Low blood pressure
How is B12 absorbed and secreted?
Vitamin B12 in food is usually bound to protein. It is related to the protein by the combined action of gastric hydrochloric acid and pepsin and then binds to an intrinsic factor, which is secreted by the stomach. The B12 intrinsic factor complex is absorbed into the bloodstream in the ileum part of the small intestine.
Who is at risk for Vitamin B12 deficiency?
Malabsorption of vitamin B12 is most commonly seen in the elderly, second to gastric achlorhydria (low or absent hydrochloric acid). The symptoms of subclinical deficiency are subtle and often not recognized. Also, long-term use of certain medications causes vitamin B12 deficiency due to interaction with vitamin B12.
The following most common medications prescribed are known to cause B12 deficiency and the symptoms of low B12.
Acid-suppressive therapy: Histamine-2 (H2) blockers and proton pump inhibitors (PPI) have been reported to inhibit the absorption of vitamin B12.
- H2 blocker drugs include:
- Ranitidine (Zantac)
- Nizatidine (Axid)
- Famotidine (Pepcid)
- Cimetidine (Tagament)
- PPI drugs include:
- Omperazole (Prilosec, Prilosec OTC, Zegerid)
- Lansoprazole (Prevacid)
- Pantoprazole (Protonic)
- Rebeprazole (Aciphex)
- Esomeprazole (Nexium)
- Dexlansoprazole (Dexilant)
Gentamicin: Intramuscular administration of B12 (methylcobalamin) protects against the development of gentamicin-induced ototoxicity in guinea pigs.
Examples of glucocorticoids drugs include:
Metformin: Metformin, most commonly used to treat type 2 diabetes, has been reported to inhibit the absorption of vitamin B12. All my patients who have been on Metformin for longer than three months are vitamin B12 deficient. Our long-term goal with this group of patients is to reverse type 2 diabetes, so there would be no long-term need for Metformin use, and hence prevent vitamin B12 deficiency.
1. Dr. D’Souza, Jonathan. The 4 Types Of Vitamin B12 Supplements & Which One You Should Be taking. Bit.ly/whymethylcobalamin. Accessed July 2, 2017.
2. Gaby, Alan R. 2011. Nutritional Medicine. Concord, N.H: Fritz Perlberg Publishing.
3. O’Leary F, Samman S. Vitamin B12 in health and disease. Nutrients. 2010;2(3):299-316