B12 deficiency

Your body needs vitamin B12 in order to create red blood cells and keep the nervous system healthy. It is also needed to absorb folic acid and it helps to release energy. B12 is absorbed through your intestines from a variety of foods, but mainly meat, fish and dairy products. It can be stored in the body in small amounts, and around 80% of this is stored in the liver. It may take three or four years for the symptoms of deficiency to develop.

Vitamin B12 cannot be absorbed on its own. It has to combine with another substance called 'intrinsic factor', which is produced by your stomach lining.

Vitamin B12 deficiency usually develops for one of the following reasons:

  • Your stomach cannot produce enough intrinsic factor.
  • Your intestine cannot absorb enough vitamin B12.
  • You do not eat enough food containing vitamin B12 (this may happen to people following a vegan diet).

Red blood cells


Red blood cells transport oxygen around the body and remove carbon dioxide.

Liver


The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.

Deficiency

If you have a deficiency it means you are lacking in a particular substance needed by the body.

Stomach


The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.

Vitamin B12 is needed by all cells of the body in order to allow them to multiply. A shortage of vitamin B12 mainly affects red blood cells, because millions need be made every minute. A lack of red blood cells can lead to anaemia. The common symptoms of anaemia are tiredness, shortness of breath and palpitations.

There is also a type of B12 deficiency anaemia caused by lack of intrinsic factor. This is called pernicious anaemia. A shortage of intrinsic factor means that B12 cannot be absorbed properly. Pernicious anaemia has the same symptoms as anaemia, including tiredness, shortness of breath and fatigue. Other symptoms of anaemia can include:

  • soreness of the tongue,
  • loss of weight,
  • pale skin, often with a lemon tint,
  • intermittent diarrhoea,
  • menstrual problems, and
  • poor resistance to infections.

If the deficiency goes on too long, the nervous system is liable to be affected, causing:

  • tingling of the fingers and toes,
  • muscle weakness,
  • staggering,
  • tenderness in the calves, and
  • confusion.

Glossary

Fatigue
Fatigue is extreme tiredness and lack of energy.
Diarrhoea
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Red blood cells
Red blood cells transport oxygen around the body and remove carbon dioxide.
Deficiency
If you have a deficiency it means you are lacking in a particular substance needed by the body.
Palpitations
Palpitations refer to an irregular heartbeat, or the sensation of skipped or extra heartbeats.

The immune system normally makes antibodies to attack bacteria and viruses. Pernicious anaemia is caused by an autoimmune disease, which causes the immune system to make antibodies against other parts of your body. In pernicious anaemia, antibodies are formed that attack the stomach lining and damage the cells that produce intrinsic factor. This stops intrinsic factor from attaching to B12, and so the vitamin cannot be absorbed into your body.

Another cause is where the bowel cannot absorb the vitamin B12 because it has been damaged by disease (e.g. Crohn's disease) or shortened by surgery (usually to treat bowel disease). If the bowel has been shortened by surgery, these problems can contribute to a condition known as short bowel syndrome. Short bowel syndrome is a group of problems affecting people who have had half or more of their small intestine removed. Common symptoms are diarrhoea, cramping and heartburn. Some people become malnourished because their remaining small intestine is unable to absorb enough water, vitamins, and other nutrients from food.

Occasionally, some people who follow a vegan diet may become deficient in B12. This is because B12 is not found in vegetable foods (such as fruit, vegetables and grains).

Glossary

Immune
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Diarrhoea
Diarrhoea is the passing of frequent watery stools when you go to the toilet.
Antibodies
Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
Stomach
The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.
Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.
Heartburn
Heartburn, also known as indigestion, is a painful, burning discomfort felt in the chest, usually after eating.

Your GP will normally carry out a physical examination to look for signs of vitamin B12 deficiency, such as a rapid pulse and pale skin. A blood test may be taken to check the number and appearance of red blood cells. People with a B12 deficiency have large red blood cells that look unusual. Laboratory tests can also be used to measure the level of vitamin B12 in the blood.

Sometimes, your GP may want to check your blood for intrinsic factor antibody levels. This test is used to identify whether you have pernicious anaemia, as most people who lack intrinsic factor have these antibodies in their blood.

Occasionally, a biopsy of bone marrow may be taken to confirm the diagnosis. It can be used to rule out other causes of anaemia and red cell abnormalities.

Glossary

Deficiency
If you have a deficiency it means you are lacking in a particular substance needed by the body.
Red cell
Red blood cells transport oxygen around the body and remove carbon dioxide.
Biopsy
A biopsy is a test that involves taking a small sample of tissue from the body so it can be examined.
Blood test
During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Bone marrow
Bone marrow is the soft, spongy tissue in the centre of bones that produces blood cells.
Antibodies
Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.

B12 deficiency is treated with a course of vitamin injections. A form of vitamin B12 known as hydroxocobalamin is injected into a muscle once every two to four days. Around six injections are given, which is enough to build up a store of vitamin B12 in the body.

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.

It is common to need maintenance injections of vitamin B12 every three months for life to stop the problems coming back.

Glossary

Blood test
During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory.
Deficiency
If you have a deficiency it means you are lacking in a particular substance needed by the body.

Strict vegetarians (who do not eat eggs) and vegans can help to prevent B12 deficiency by choosing breakfast cereals fortified with B12, and taking mineral supplements. Most people should be able to get all the B12 they need by eating a balanced diet containing meat, fish and dairy foods.

Glossary

Deficiency
If you have a deficiency it means you are lacking in a particular substance needed by the body.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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