What are the causes of vitamin B12 deficiency?

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Pernicious anaemia

Normally, when you eat foods with vitamin B12, the vitamin combines with a protein called intrinsic factor in the stomach. The combined vitamin B12/intrinsic factor is then absorbed into the body further down in the gut. (Intrinsic factor is made by cells in the lining of the stomach and is needed for vitamin B12 to be absorbed.)

Pernicious anaemia is the common cause of B12 deficiency. It is due to an 'autoimmune disease'. The immune system normally makes antibodies to attack bacteria, viruses and other 'germs'. If you have an autoimmune disease, the immune system makes antibodies against certain tissues of your body. If you have pernicious anaemia, antibodies are formed against your intrinsic factor, or against the cells in your stomach which make intrinsic factor. This stops intrinsic factor from attaching to vitamin B12, and so the vitamin cannot be absorbed into your body. It is thought that something triggers the immune system to make antibodies against intrinsic factor. The 'trigger' is not known.

Pernicious anaemia usually develops over the age of 50. Women are more commonly affected than men, and it tends to run in families. It occurs more commonly in people who have other autoimmune diseases such as thyroid diseases and vitiligo. The antibodies which cause pernicious anaemia can be detected by a blood test to confirm the diagnosis.

Stomach or gut problems

Past surgery to remove the stomach or certain parts of the gut will mean absorption of vitamin B12 may not be possible. Some diseases which affect the area of gut where vitamin B12 is absorbed may affect the absorption of the vitamin. For example, Crohn's disease.

Dietary causes

It is unusual to lack vitamin B12 if you eat a normal diet. Strict vegans who take no animal or dairy produce may become vitamin B12 deficient.

What is the treatment for vitamin B12 deficiency?

You will need vitamin B12 injections. About six injections are given at first, one every 2-4 days. This quickly builds up the body's store of vitamin B12. Vitamin B12 is stored in the liver. Once a store of vitamin B12 is built up, this can supply the body's needs for several months. An injection is then only needed every three months to top up the supply.

The injections are needed for life. You should have no side-effects from the treatment as it is simply replacing a vitamin that you need.

Follow up

The symptoms of anaemia usually improve quickly once treatment has begun. You may be advised to have a blood test every year or so. This will check that the anaemia is being treated successfully. A blood test may also be done to see that your thyroid gland is working well. (Thyroid problems are more common in people with pernicious anaemia.)
If you have pernicious anaemia, you have an increased chance of developing cancer of the stomach. It is about three times the normal chance, which means that about 4 in 100 people with pernicious anaemia develop stomach cancer (even when the anaemia is treated). See a doctor soon if you develop any stomach symptoms such as regular indigestion or stomach pain.

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