Vitamin B12 deficiency (anaemia or pernicious anaemia)

Reviewed by: Dr Patrick Davey, Cardiologist and Dr Rachel Green,
Consultant Haematologist

What is anaemia?

Meat, fish and cheese are all good sources of vitamin B12.
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Anaemia is a deficiency of red blood cells which can lead to a
mild lack of oxygen causing unusual tiredness. Red blood cells are
manufactured in the bone marrow and have a life expectancy
of approximately four months. Anaemia occurs either through
the reduced production of red blood cells or an increased
loss of red blood cells.

What are red blood cells?

Red blood cells are the cells which circulate in the blood
plasma (fluid). Through its pumping action, the heart propels
the blood around the body through the arteries. The red blood
cells obtain oxygen in the lungs and carry it to all the
body's cells.

The cells use the oxygen to fuel the combustion (burning) of
sugar and fat which produces the body's energy.

During the use of the muscles, carbon dioxide is created as
a waste product. It binds itself to the red blood cells
which have delivered their load of oxygen. The carbon dioxide
is then transported back to the lungs where it is exchanged
for fresh oxygen by breathing.

Why does a vitamin B12 deficiency cause anaemia?

To produce red blood cells, the body needs, among other things,
iron, vitamin B12 and folic acid (one of the B group of vitamins).
If there one or more of these ingredients is lacking,
anaemia will develop.

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

B12 deficiency is frequently caused either by the inability
of the small bowel to absorb B12, or by a lack of food
containing B12.

It frequently occurs in elderly people although it may also be
present in the young, particularly women.

What are the causes of vitamin B12 deficiency?

A vegetarian or vegan diet can cause vitamin B12 deficiency
because vitamin B12 is only found in foods of animal origin,
such as meat, liver, fish, eggs and milk.
In the UK, by far the most common cause of B12 deficiency
is a lack of 'Intrinsic Factor' a substance which is produced
in the stomach and enables the body to absorb vitamin B12
from the diet.

Causes for a reduced production of intrinsic factor are:

The formation of antibodies against the cells producing
intrinsic factor. The cells then die and B12 deficiency and
anaemia (also called pernicious anaemia) develop.

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

Diseases of the small intestine, fish tapeworm and the
after-effects of surgery to the small intestine can all mean
that the surface of the small intestine is too small to
obtain B12 and intrinsic factor effectively.

What are the symptoms of anaemia due to vitamin B12 deficiency?

The first symptoms will be unusual tiredness, difficulty in
breathing and dizziness.

Further symptoms specific to B12 deficiency are:
A red, irritated and possibly shiny, tongue
A reduced sense of taste
Altered or reduced sense of touch
Reduced sense of vibration (an inability to feel the vibrations
of a tuning fork)

Some people with B12 deficiency will experience symptoms in their
nervous system first.

Headache

Psychological symptoms

Pains in the legs (intermittent claudication), difficulties
with walking and coordination will gradually occur together
with muscle spasm paralysis

A less sensitive sense of touch

Shortness of breath, palpitation and chest pains (angina)

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

What can be done to avoid vitamin B12 deficiency?

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

Because vitamin B12 is only found in food of animal origin,
strict vegetarians should take B12 supplements to avoid deficiency

If a family member also suffers from pernicious anaemia extra
care should be taken to prevent deficiency

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

How does the doctor diagnose vitamin B12 deficiency and anaemia?

First the doctor must be sure that the patient is suffering from
anaemia.

A blood sample will be taken and an analysis of the red blood
cells will usually be included. In cases of 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 patient will be given the Schilling test
to measure 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 show if the patient has any antibodies to
intrinsic factor or to other organs in the body.

What can the doctor do?

Examine the patient and prescribe treatment to deal with the
causes of the disease

Prescribe vitamin B12 injections. These are given every three
months and will usually be continued throughout the patient's
life. They have few side effects.

Prognosis

By eliminating the cause and taking the necessary vitamins
by supplement or injection, there will be a complete recovery.

However, even if the pernicious anaemia is treated, there is
a slightly increased risk of cancer of the stomach and if the
treatment is started too late there is a risk of permanent
damage to the nervous system.