Vitamin B12
Vitamins and MineralsVitamin B12

Vitamin B12

Vitamin B12

June 25, 2020

Vitamins and Minerals

What is Vitamin B12?

Vitamin B12 or Cobalamin is one of the eight B complex vitamins. It is a water-soluble vitamin that plays a fundamental role in the formation of red blood cells and the maintenance of the central nervous system.

Vitamin B12 cannot be produced by the body and needs to be supplied by the diet. It is mostly found in animal products, including meat, fish, dairy products and eggs.

People that exclude all animal products from their diet, for example vegans, have therefore a higher risk of being deficient of vitamin B12 if they do not eat fortified food or take supplements. Older people and people who have undergone gastric bypass operation can have problems absorbing enough vitamin B12 from food and therefore also have a higher risk of not getting enough vitamin B12.

Prolonged vitamin B12 deficiency often leads to anaemia, which is a condition in which you do not have sufficient amounts of healthy red blood cells to carry an adequate amount of oxygen around your body. However, it is also possible to have vitamin B12 deficiency without any sign of anaemia on the full blood count. Low vitamin B12 levels in the blood has been associated with decreased cognitive function in the elderly.

For more information about vitamin B12 and pregnancy specifically, click here.

Why is this analysis important?

Measurement of vitamin B12 levels in the blood is usually carried out to rule out or confirm vitamin B12 deficiency. Early signs of vitamin B12 deficiency can be very vague and nonspecific. It is especially important for people following a vegetarian or vegan diet, older people and those who have undergone a gastric bypass operation to regularly check their vitamin B12 levels in the blood to ensure that they get enough vitamin B12.

Doctors can also order a vitamin B12 test for the investigation of anaemia symptoms such as fatigue, paleness and shortness of breath or neurological symptoms such as memory problems, difficulty to concentrate or tingling/numbness/burning sensation in the hands and feet.

In short, it is useful to analyse vitamin B12 levels in the blood to:

  • Confirm or rule out vitamin B12 deficiency

  • Investigate the cause of anaemia (low blood count)

  • Investigate the cause of worsening cognitive ability and nervous system problems


The reference range for vitamin B12 levels in the blood can be different depending on the laboratory and technique used. Doctors usually also take into account a number of factors when evaluating vitamin B12 values.

High Vitamin B12 levels in the blood may be associated with:

  • Intake of supplements containing high amounts of vitamin B12

  • Liver diseases (such as cirrhosis or hepatitis)

  • Some types of blood cancer (leukemia)

Low Vitamin B12 levels in the blood may be associated with:

  • Diet poor in vitamin B12, as in vegan or vegetarian diets

  • Prolonged use of antacids, proton pump inhibitors (eg Omeprazole), H2 receptor inhibitors (eg Ranitidine), or Metformin

  • Atrophic gastritis

  • Helicobacter Pylori infection

  • Pancreatic insufficiency

  • After treatment with some antibiotics that alter the intestinal flora

  • Pernicious anaemia (an autoimmune disease that prevents the absorption of Vitamin B12)

  • Gastrectomy or gastric bypass surgeries

  • Hyperthyroidism

Other Considerations

Folate (vitamin B9) and vitamin B12 are associated with each other in many bodily processes. Deficiency in folate and vitamin B12 can lead to very similar symptoms. Folate levels can also be elevated in people with Vitamin B12 deficiency. Therefore, analysis of folate and vitamin B12 levels in the blood are usually carried out simultaneously.

Some individuals can have a so-called functional vitamin B12 deficiency, which means that even though their vitamin B12 level in the blood is within the reference range, they still do not have enough vitamin B12. Therefore, further testing can be necessary if clear symptoms of vitamin B12 deficiency are present.

Tests that include this marker


Causes and pathophysiology of vitamin B12 and folate deficiencies. Stanley L Schrier, MD. UpToDate Jul 02, 2018

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