Vitamin B12

Vitamin B12, also known as cobalamin, was the last true vitamin to be discovered (in 1948). It is water-soluble and contains the metal cobalt -- the only known function of cobalt in the human body.

Vitamin B12 is absorbed in the lower part of the small intestine, but only if a special carrier protein, called 'intrinsic factor', is present. Intrinsic factor is made in the stomach, and vitamin B12 deficiency can develop due to a lack this or acid production in the stomach, as well as disease of the small intestine (e.g. Crohn's). Unlike most water soluble vitamins, B12 can be stored in the body (to a certain extent) because our livers hold enough of it to last several years.

Prolonged deficiency leads to pernicious anaemia and other symptoms. If the deficiency is not corrected, your nerves in the spinal cord can be damaged, leading to a rare condition known as 'sub-acute' -- combined degeneration of the cord. Lack of vitamin B12 may be masked by taking folic acid supplements, which correct the changes that would otherwise be seen in red blood cells. If taking folic acid supplements, it is therefore important to ensure you also have a good intake of vitamin B12. This is especially important for vegetarians (see below).

Why you need it

Vitamin B12 is needed together with another vitamin, folic acid, when new genetic material (DNA) is made during cell division. It is most needed by cells with a rapid turnover, such as those found lining the gut (shed, on average, every three days), cells in hair follicles, and in the marrow which is continually producing new red blood cells. Lack of vitamin B12 causes production of cells that are larger than they should be which, in the case of red blood cells, leads to a form of anaemia.

Vitamin B12 also plays a role in the formation of healthy nerve sheaths (myelin) needed for the transmission of electrical signals down nerve endings. It is also needed for healthy immunity, appetite and for healing during convalescence.


Together with folic acid, vitamin B12 seems to protect against some congenital developmental disorders (neural tube defects) such as spina bifida.

A raised blood level of the amino acid, homocysteine is now recognized as an important risk factor for developing coronary heart disease and stroke. Homocysteine is formed in the body from the breakdown of the dietary amino acid, methionine. Normally, its level is tightly controlled by three different enzymes that convert homocysteine to cysteine - a safe end product used by cells for growth. When certain B vitamins are lacking, including vitamin B12, this conversion cannot occur so efficiently, and potentially harmful levels of homocysteine build up in the circulation. Taking supplements of B group vitamins (folic acid plus vitamins B6 and B12) has been shown to lower homocysteine levels in people with raised homocysteine levels - especially the elderly.

Research suggests that lack of vitamin B12 can be associated with infection of the stomach with Helicobacter pylori. Helicobacter pylori is a form of bacteria that burrows into the stomach lining to trigger inflammation. Although it doesn't cause symptoms in everyone, virtually all patients with duodenal ulcers are infected, plus three quarters of those with gastric ulcers. H pylori infection is also associated with an increased risk of gastric cancer.

How much you need

The EC RDA for vitamin B12 is 1mcg.

Low vitamin B12 levels are common in the elderly, both because of reduced dietary intake and reduced absorption from the gut (malabsorption), linked with reduced production of hydrochloric acid in the stomach.

Although vitamin B12 supplements to treat pernicious anaemia are traditionally given as regular injections, it can be taken orally in a very high dose (e.g. 2mg = 2000mcg daily). Research is also currently looking at giving it by absorption through the mucus membranes of the mouth or nose.

Symptoms that may be due to vitamin B12 deficiency

  • anaemia
  • smooth, sore tongue
  • shortness of breath
  • tiredness tiredness
  • exhaustion
  • menstrual disorders
  • numbness
  • tingling
  • trembling
  • clumsiness
  • difficulty walking, especially in the dark, when you can't see where you are going
  • poor memory
  • lack of concentration
  • confusion
  • depression

Lack of B12 causes a variety of nervous system symptoms, including psychiatric changes and a serious condition known as sub acute combined degeneration of the spinal cord. Because the symptoms are so variable, vitamin B12 deficiency should be checked for in all spinal cord, nerve and psychiatric disorders.

Foods containing vitamin B12 include

  • liver
  • kidney
  • oily fish - especially sardines
  • red meat
  • white fish
  • eggs
  • milk
  • yogurt
  • cheese

Vegetarians, especially vegans, are at risk of getting vitamin B12 deficiency. Vitamin B12 is only found in animal-based foods. No natural plant products contain consistent amounts of vitamin B12, with the possible exception of blue-green algae. There is some controversy over whether the B12 they contain is in an active form. Vitamin B12 is also made by bacteria, and supplements containing B12 derived from bacterial cultures are available that are ethically acceptable to most vegetarians.

Vitamin B12 supplements are best taken together with folic acid (folate) supplements.

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