Anaemia due to vitamin B12 deficiency (pernicious anaemia)

Anaemia due to vitamin B12 deficiency (pernicious anaemia)

What is anaemia?
You get anaemia when you don't have enough red blood cells. This makes it difficult for your blood to carry oxygen, causing unusual tiredness and other symptoms.

The number of red blood cells can drop if there is:


a reduction in the number of red blood cells produced


an increase in the loss of red blood cells.
Red blood cells and oxygen

Through its pumping action, the heart propels blood around the body through the arteries.

The red blood cells take up oxygen in the lungs and carry it to all the body's cells. Your cells use this oxygen to fuel the combustion (burning) of sugar and fat which produces the body's energy.

During this process carbon dioxide is created as a waste product. It binds itself to the red blood cells that have delivered the oxygen.

The red blood cells then transport the carbon dioxide back to the lungs. We exchange this carbon dioxide for fresh oxygen by breathing.

This process is called oxidation.


Why does vitamin B12 deficiency cause anaemia?

Red blood cells are made in the bone marrow and circulate in the blood. They only have a life expectancy of about four months.

The body needs iron, vitamin B12 and folic acid (one of the B group of vitamins) to produce more red blood cells. If there is a lack of one or more of these nutrients, anaemia will develop.

Anaemia due to a lack of vitamin B12 is also called pernicious anaemia.

Vitamin B12 is essential for the nervous system, which is why a deficiency can also cause inflammation of the nerves (neuritis) and dementia (mental deterioration).

Elderly people are particularly at risk of vitamin B12 deficiency, although it may also be present in the young women.

What causes this type of anaemia?


Not eating enough foods that contain vitamin B12. A vegetarian or vegan diet can cause deficiency because vitamin B12 is only found in foods of animal origin, such as meat, fish, eggs and milk.


Inability of the small intestine to absorb vitamin B12. The stomach produces a substance called intrinsic factor to absorb vitamin B12 from food. In the UK, the most common cause of B12 deficiency is a lack of intrinsic factor.


What causes a low production of intrinsic factor?


Antibodies can form against the cells that produce intrinsic factor. The cells then die, leading to B12 deficiency and anaemia.


Stomach cancer and ulcers can take up so much room in the stomach that there are too few cells left to produce intrinsic factor.


Diseases of the small intestine, fish tapeworm and the after-effects of bowel surgery can all result in the surface of the small intestine being too small to absorb B12 and intrinsic factor effectively.




What are the symptoms of this type of anaemia?

If a person is otherwise healthy, it can take some time for the signs of anaemia to appear.


The first symptoms will be tiredness and palpitations (awareness of heartbeat).


Shortness of breath and dizziness (fainting) are also common.


If the anaemia is severe, it can result in angina (chest pain), headache and leg pains (intermittent claudication).


Red, sore tongue and mouth.


Weight loss.


Diarrhoea.


Some people with vitamin B12 deficiency will experience symptoms in their nervous system first, such as:


altered or reduced sense of touch


less sensitivity to vibration (inability to feel the vibrations of a tuning fork)


colour blindness


tingling in the hands and feet


muscle weakness


difficulties with walking and coordination


psychological symptoms such as memory loss, confusion and depression.


With pernicious anaemia there is an increased danger of developing stomach cancer.

How is pernicious anaemia diagnosed?

A blood sample is taken and sent off to the laboratory. An analysis of the red blood cells is usually included with the result of the test.

In cases of vitamin B12 deficiency, the red blood cells will be the usual colour but larger than normal.

If the blood test shows a low vitamin B12 count, it must be established whether it is pernicious anaemia or if there is some other cause.

The Schilling test measures the body's ability to absorb vitamin B12 from the bowel. This will show whether the anaemia is caused by a lack of intrinsic factor.

Blood tests will also confirm if you have any antibodies to intrinsic factor.

How is pernicious anaemia treated?

Your GP will prescribe vitamin B12 injections. These are given every three months and will usually be continued throughout life. The injections have few side-effects.

Even if the pernicious anaemia is treated, there is a slightly increased risk of stomach cancer.

While the injections can cure vitamin B12 deficiency, if the treatment is started too late there is a risk of permanent damage to the nervous system.

What can be done to avoid vitamin B12 deficiency?


Eat a varied diet. Good sources of vitamin B12 are liver, fish and eggs.


Vegans should take vitamin B12 supplements to avoid deficiency.


If a family member has pernicious anaemia, you should take extra care to prevent deficiency.


Anyone who has undergone surgery in their small intestine or stomach should pay attention to any of the symptoms mentioned above.