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Vitamin B12 deficiency anaemia

Key points

  • You need vitamin B12 for many important processes, such as making red blood cells and keeping your nerves healthy.
  • Good sources of vitamin B12 include meat and other animal products, such as eggs and cheese, and fortified cereals.
  • Depending on what’s causing your deficiency, you may need to have vitamin B12 injections.

Vitamin B12 deficiency anaemia is a type of anaemia that you can get if you don't have enough vitamin B12 in your body. Anaemia is a condition in which your blood can’t carry enough oxygen to meet the needs of your body.

About vitamin B12 deficiency anaemia

You need vitamin B12 for many important processes inside your body, particularly for making red blood cells and keeping your nerves healthy. If you don’t have enough vitamin B12, your body won't be able to make as many red blood cells as normal. They will also be abnormally large and won't last as long as they should do.

If you don't have enough red blood cells, your tissues and organs may not get enough oxygen. This leads to the symptoms of anaemia.

Symptoms of vitamin B12 deficiency anaemia

Common symptoms of all types of anaemia include:

  • feeling tired
  • feeling short of breath
  • feeling your heart racing or thumping, which is called palpitations

If you have vitamin B12 deficiency anaemia, you may also develop problems such as:

  • losing your appetite
  • a sore mouth and tongue, which is called glossitis
  • diarrhoea
  • poor concentration and forgetfulness
  • depression
  • tingling, numbness and burning in your feet, hands, arms and legs
  • difficulty walking
  • poor vision

These symptoms may be caused by problems other than vitamin B12 deficiency anaemia. If you have any of these symptoms, see your GP for advice.

Complications of vitamin B12 deficiency anaemia

If you have anaemia, your heart has to work harder to deliver oxygen to your vital organs. If you don't get treatment, this can lead to problems with your heart and lungs. Vitamin B12 deficiency can also affect your nervous system and your movement, vision and co-ordination. It may also increase your risk of infertility and is associated with a slightly increased risk of stomach cancer.

However, if you get treatment for vitamin B12 deficiency anaemia, these complications are reversible.

Causes of vitamin B12 deficiency anaemia

The most common cause of vitamin B12 deficiency is pernicious anaemia. This is a condition that usually develops when your body lacks a protein called intrinsic factor. Normally, intrinsic factor is released by cells in your stomach lining, where it attaches to vitamin B12. This vitamin B12-intrinsic factor complex then enters your small bowel where it's absorbed into your bloodstream.

In pernicious anaemia, antibodies produced by your immune system attack the intrinsic factor when it’s released into your stomach. Or, they may attack the cells in your stomach lining that produce the intrinsic factor. Pernicious anaemia tends to run in families and is most common in people aged between 40 and 70.

Another reason for becoming deficient in vitamin B12 is if your small bowel is unable to absorb the vitamin B12-intrinsic factor complex. You then become deficient and develop anaemia.

Other causes of vitamin B12 deficiency anaemia are listed below.

  • Diet. Vitamin B12 is only found in meat and animal products, so if you follow a vegan diet, you may not get a sufficient amount for your needs.
  • Surgery. You can become deficient in vitamin B12 if you’ve had surgery to remove part of your stomach or small bowel
  • Bowel disease. If you have Crohn's or coeliac disease disease, for example, it can interfere with vitamin B12 absorption.
  • Medicines. Certain medicines, such as the antibiotic neomycin, the diabetes medicine metformin, and anticonvulsants, can interfere with vitamin B12 absorption.
  • Pregnancy. This can reduce your levels of vitamin B12.

Sometimes, children are born unable to produce enough intrinsic factor, or to absorb the combination of intrinsic factor and vitamin B12 in their small bowel.

Diagnosis of vitamin B12 deficiency anaemia

Your GP will ask about your symptoms and examine you. He or she may also ask about your medical history. If your GP suspects you have anaemia, he or she will ask you to have a blood test. Your blood will be sent to a laboratory to be tested for the following.

  • A full blood count. This is to check the level of haemoglobin in your blood and how many of each of the different types of blood cell you have. It also checks the size of your red cells and the amount of haemoglobin in each red cell.
  • Vitamin B12, iron and folate. This is to measure the levels of each of these in your blood.
  • A blood film. Your blood will be examined under a microscope to check the size and shape of your red blood cells. The different white cells that are present will also be assessed.
  • Intrinsic factor antibodies. If you have these antibodies in your blood, it may be a sign that you have pernicious anaemia.

You may need to have further tests to help identify the cause of your anaemia. Your GP may refer you to a haematologist (a doctor who specialises in identifying and treating conditions of the blood). Or your GP may refer you to see a gastroenterologist (a doctor who specialises in identifying and treating conditions that affect the digestive system).

Treatment of vitamin B12 deficiency anaemia

Your GP will try to identify why you’re deficient in vitamin B12 so that he or she can treat any underlying cause.


If you’re not getting enough vitamin B12 in your diet, your GP may advise you on how to adjust your diet, or refer you to a dietitian. Good sources of vitamin B12 include:

  • red meat and other animal products, such as eggs and cheese
  • salmon
  • yeast extract
  • fortified breakfast cereals and bread (this means that vitamin B12 has been added during manufacturing)


Your GP may advise you to take vitamin B12 supplements (cyanocobalamin) to make up for any shortage of vitamin B12 in your diet. He or she will usually recommend you take 50 to 150 milligrams daily between meals. Your GP will check the level of vitamin B12 in your blood after around eight weeks. Always read the patient information leaflet that comes with your supplements. If you have any questions, ask your GP or pharmacist for advice.

Depending on what’s causing your vitamin B12 anaemia, supplements may not be suitable for you. Your doctor may suggest you have injections of vitamin B12 (hydroxocobalamin) into a muscle, instead. Possible side-effects of vitamin B12 injections include:

  • feeling sick
  • a headache
  • feeling dizzy
  • a skin rash

If you have problems absorbing vitamin B12, such as in pernicious anaemia, you will need to have injections for the rest of your life. You will have these every two to three months.

Your GP will need to monitor you to check that your treatment is working. About 10 days after you start treatment, you may be asked to have a repeat blood count to make sure there is an improvement. You will have another blood test after about eight weeks to confirm that your haemoglobin and red blood cell levels have returned to normal.

If you have severe vitamin B12 deficiency anaemia, your doctor may suggest you consider having a blood transfusion. However, most people usually respond quickly to treatment with injections. Speak to your GP for more information.

Prevention of vitamin B12 deficiency anaemia

You only need a very small amount (1.5 micrograms) of vitamin B12 each day. If you eat a healthy, balanced diet and don't have a condition that affects your absorption of vitamin B12, you're unlikely to have a shortage.

Good sources of vitamin B12 include meat and other animal products, such as eggs and cheese. Some breakfast cereals and bread are fortified with vitamin B12. This means that vitamin B12 has been added during manufacturing.

If you eat a vegan diet, try to include foods fortified with vitamin B12. Your GP may suggest you take regular vitamin B12 supplements to prevent anaemia.


Reviewed by Rachael Mayfield-Blake, Bupa Health Information Team, November 2013.

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For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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