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Vitamin B12-deficiency anaemia

Published by Bupa's health information team, February 2008.

This factsheet is for people who have anaemia caused by a lack of vitamin B12, or who would like information about it.

Anaemia is a condition where you have too few red blood cells or not enough haemoglobin in your blood. It can make you feel tired, breathless and faint.

About Vitamin B12-deficiency anaemia
Symptoms
Causes
Diagnosis
Treatment
Prevention
Further information
Questions and answers
Related topics
Sources

About Vitamin B12-deficiency anaemia

As well as causing symptoms of anaemia, a lack of vitamin B12 can also affect the nerves, and so affect the senses of touch and pain.

In adults, blood cells are made by red bone marrow, which is found inside the centre of the hips, ribs, breastbone and backbone, plus the ends of long bones such as the thigh. Red blood cells live for around 120 days before they are broken down and replaced, as part of a normal renewal process.

Vitamin B12 is a crucial ingredient in DNA, the chemical that carries genetic information for new cells. It's found in meat and animal products but not in vegetables. You need vitamin B12 to make red blood cells and for maintaining healthy nerves.

Symptoms

The symptoms of anaemia include:

breathlessness
feeling very tired
dizziness
feeling very cold all the time
a rapid, weak pulse
palpitations
headaches

People with vitamin B12-deficiency anaemia may also look pale or jaundiced (yellow-tinged skin and eyes).

As well as the symptoms of anaemia, vitamin B12 deficiency may cause neurological symptoms due to inflammation of the nerves (neuritis). This is called vitamin B12 neuropathy. It affects movement and sensation, especially in the legs, and causes numbness or pins and needles. It can also cause confusion, depression, poor concentration and forgetfulness.

Causes

There are many different causes of anaemia. A deficiency of vitamin B12 in your diet is just one possible cause.

Other nutrients that you need to make red blood cells include iron and folate (folic acid). A lack of these in the diet can also cause anaemia.

Most people who develop vitamin B12-deficiency anaemia can't produce enough of a substance called intrinsic factor in their stomach. This intrinsic factor is needed for vitamin B12 to be absorbed from food and drink. This is a condition called pernicious anaemia.

Pernicious anaemia is an autoimmune condition. Normally, antibodies produced by the body's immune system attack foreign substances such as viruses and bacteria. With autoimmune conditions, the immune system mistakes the person's own tissue as foreign and attacks it instead.

With pernicious anaemia, antibodies damage the cells in the stomach that produce intrinsic factor. The exact cause of pernicious anaemia isn't known. It's most common in people aged over 60. It affects women more than men, and is more common in people with blue eyes, early greying hair and blood group A. It also tends to run in families, especially if other autoimmune diseases run in the family. Pernicious anaemia can cause severe illness if it isn't treated.

Other causes of vitamin B12 deficiency include the following.

Parasites or bacteria. Poor absorption of vitamin B12 can be caused by parasites or having too many bacteria in the small intestine, which interfere with absorption of food.
Crohn's disease (a type of inflammatory bowel disease) - this can also interfere with vitamin B12 absorption.
Damage to the pancreas, liver or stomach. Vitamin B12 deficiency can be triggered if your pancreas isn't working properly, if you have liver damage (eg due to drinking excess alcohol) and by the surgical removal of part or all of your stomach.
Diet. Having a deficiency of vitamin B12 just because of eating a poor diet is rare in Western countries. But strict vegans may be at risk because their diet excludes meat and animal products - the foods that provide this vitamin. Vitamin B12 is the only vitamin that is not found in vegetables.

Diagnosis

If you have symptoms of anaemia, such as pale skin, weakness and fatigue, you should visit your GP. He or she will ask about your symptoms, medical history and current eating habits, and may examine you.

If your doctor suspects you have vitamin B12 deficiency anaemia, he or she will probably ask you to have a blood test called a full blood count (FBC).

The normal amount, or concentration, of haemoglobin for adults is at least 13.5g/dl for men (this is 13.5 grams of haemoglobin per decilitre of blood - a decilitre is 100ml) and 11.5g/dl for women. Levels lower than this show that you have anaemia.

Your doctor will also look at the size of your red blood cells from your blood sample.

Enlarged red cells are caused by vitamin B12 (and/or folate) deficiency. If they are found in the test, the condition is called macrocytic anaemia. Finding enlarged red cells in the blood can help to diagnose anaemia but does not show what has caused it.

The level of vitamin B12 can be measured with a blood test. If you have low levels of vitamin B12 in your blood, you may need to have further blood tests - for example tests for the antibodies that cause pernicious anaemia - to work out what has caused your anaemia.

Treatment

The treatment for vitamin B12 deficiency anaemia is usually injections of vitamin B12. The number of injections you need to have will depend on the exact type and severity of your anaemia. Vitamin B12 injections can sometimes cause bruising and soreness.

Prevention

You only need a small amount of vitamin B12 each day - about 1.5 micrograms. If you eat a healthy balanced diet, and don't have pernicious anaemia, you are unlikely to have a shortage. However, your body can't store vitamin B12 and you need a daily supply.

Good sources of vitamin B12 include meat and animal products, such as beef, liver, salmon, cod, cheese, yeast extract and eggs. Some breakfast cereals are fortified with vitamin B12.

If you eat a vegetarian diet, you should consider taking a regular vitamin B12 supplement to prevent anaemia. According to the UK's Food Standards Agency, taking a supplement of 2mg (which is about 1,000 times more than the minimum required) is unlikely to do any harm.

Further information

Food Standards Agency
www.eatwell.gov.uk
British Nutrition Foundation
020 7404 6504
www.nutrition.org.uk