Vitamin B12

The human body relies on a wide spectrum of vitamins (vital amines) and minerals for good health and wellbeing. We need specific amounts of each micronutrient for proper function of our body.

Cobalamin, also known as vitamin B12, is among the most significant micronutrients as we need it for the development, myelination, and function of the central nervous system.

We also need vitamin B12 for the production of red blood cells, the synthesis of DNA, thyroid function and other functions.

Mechanism of vitamin B12 absorption

Vitamin B12 is a large molecule that requires a specific protein, intrinsic factor, for its absorption from the gut.

--Intrinsic factor is produced by the stomach parietal cells.

--In order for vitamin B12 to be absorbed, it must first bind to intrinsic factor and then be taken up by active transport across the intestine wall into the bloodstream.

--Normally, B12 accumulates in the liver, but its supply quickly ends, especially with various pathologies.

Reasons for low vitamin B12 

There are several reasons why this process may be disrupted:

Parietal cell damage: Autoimmune, gastric surgery, H. Pylori infection
Pernicious anemia: Intrinsic factor deficiency
Dietary insufficiency: Strict vegetarianism
Ileal resection: Resection of the end of the small intestine where B12 is absorbed
Diseases that interfere with ileal absorption: Crohn's, celiac, tropical sprue.
Other causes of malabsorption: pancreatic insufficiency, liver disease, bariatric surgery

Medications that interfere with vitamin B12 absorption

Vitamin B12 deficiency can also be caused by medications that decrease stomach acid production:

Proton pump inhibitors: omeprazole (Prilosec), lansoprazole (Prevacid), pantoprazole (Protonix), rabeprazole (Aciphex), esomeprazole (Nexium)

H2 blockers: cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), nizatidine (Axid)
Metformin: a medication used to treat diabetes
Diphyllobothrium latum: a type of tapeworm that can cause B12 deficiency

Some medications can also cause vitamin B12 deficiency by interfering with the binding of vitamin B12 to intrinsic factor:

--Chloramphenicol: an antibiotic

--Colchicine: a medication used to treat gout

--Doxycycline: an antibiotic

--Probiotics: "good" bacteria that are taken as a supplement or found in some foods like yogurt

--Rifamycins: a class of antibiotics that includes rifampin (Rifadin)

--St. John's wort: an herbal supplement

--Vitamin C: a vitamin found in many fruits and vegetables

How to diagnose vitamin B12 deficiency

One of the simple and wide spread measures is MCV, which is available on the common blood test (CBC), frequently performed by your doctor. vitamin B12 may be deficient if MCV values above 90 and MCHC values above 35 g / dL.

You can also directly measure vitamin B 12 level, which has very wide range.  Optimal values for adults: 550 - 800 pg / ml

Another useful test is to measure methylmalonic acid (MMA), which reflects intracellular availability of vitamin B12. 

What are the symptoms of low vitamin B12?

Mild Symptoms




--Pale skin

--Sore tongue

--Easy bruising or bleeding

--Numbness or tingling in the hands and feet

Moderate to severe symptoms

--Anemia (low red blood cell counts)

--Yellowing of the skin (jaundice)

--Mood changes

--Memory problems


--Psychosis (losing touch with reality)

--Nerve damage

--Muscle weakness

If left untreated, vitamin B12 deficiency can cause serious health problems. Complications of vitamin B12 deficiency include:

Anemia: Vitamin B12 is essential for the production of red blood cells. Red blood cells carry oxygen to all parts of your body. If you have anemia, your body does not get enough oxygen-rich blood.

Neurological problems: Vitamin B12 is needed for the proper function of your nervous system. Neurological problems caused by vitamin B12 deficiency can include numbness and tingling in your hands and feet, trouble walking, confusion, dementia, and depression.

Pregnancy problems: Vitamin B12 is important for the development of the fetus. Women who are pregnant and do not have enough vitamin B12 may be at risk for having a baby with a birth defect.

Treatment of vitamin B12 deficiency

What foods is vitamin B12 in?

Vitamin B12 deficiency can be treated with supplements. Treatment for vitamin B12 deficiency may also include eating foods that are rich in vitamin B12, such as meat, fish, poultry, eggs, and milk.

Vitamin B12 supplements

Main forms:





Cyanocobalamin is a synthetic form that can be obtained from supplements. It is not very effective and accumulation of cyanide have been raised as a concern.

Methylcobalamin and Adenosylcobalamin- active forms of B12, which are formed from the cyanocobalamine or from hydroxocobalamin

Hydroxocobalamin - is essentially a storage form and readily converts to methyl- and adenosyl-cobalamin

With problems with the gastrointestinal tract, more effect will be from Vitamin B12 in the form of a spray or tablets under the tongue.

Severe deficiency can be treated by intramusclular or subcutaneous injections of methylcobalamin, which is available throught compound pharmacy. 

Oral forms of vitamin B12 are available and sublinqual forms are preferred due to improved absorption. 

Hydroxocobalamin is a storage form and continues to be present in blood for over 12 hours. 

Here is an example of a good source of Hydroxocobalamin

Selected References:

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