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What is anaemia and what causes it?

Anaemia occurs when the concentration of the body’s red blood cells, or the oxygen-carrying pigment contained in them, haemoglobin, falls below normal levels. It is often a symptom of an underlying medical disorder. Broadly speaking, there are 3 main causes of anaemia.

Blood loss, for example, through heavy menstrual periods or gastrointestinal bleeding from an ulcer.

Defective red blood cell production, which can result from nutritional or vitamin deficiencies or a chronic illness where the bone marrow does not work properly.

Red blood cell destruction, which may be due to hereditary factors, some autoimmune disorders, or as a side effect of some drugs.

What are the signs of anaemia?

A person with anaemia often looks very pale and may also experience:


weak and rapid pulse;



dizziness, particularly when the person stands up;

shortness of breath, particularly on exertion; and

racing heart or palpitations, particularly on exertion.

However, anaemia may not be obvious, particularly in young people or people in otherwise good health, whose haemoglobin levels may fall significantly without any symptoms showing at all. In other cases symptoms may develop slowly over months or years.

Iron-deficiency anaemia

The body needs iron for red blood cell production. However, when bleeding occurs, iron is lost from the body, causing a deficiency over time. The normal dietary intake of iron can’t compensate for the amount lost and so the body’s small stores of iron become used up quickly. It is the most common form of anaemia worldwide. People most at risk include:

women of child-bearing age (because of monthly blood loss from their periods);

pregnant women (because of the drain on their iron stores by the developing baby);

breast-fed infants who are just starting a full diet (because at this stage of development the baby’s stores of iron from the mother are beginning to be depleted and there may not be enough iron in the milk); and

people with restricted diets. For those with vegetarian or vegan diets it is important to consume iron-containing foods such as lentils, dried beans and peas, wholegrain cereals (especially iron-fortified breakfast cereals), nuts and green leafy vegetables.

In men and women who have gone through the menopause, iron deficiency may indicate that gastrointestinal bleeding, perhaps in only microscopic amounts, is present.

Other forms of anaemia

Other forms of anaemia, which are less common, include the following.

Haemolytic anaemia, where red blood cells are destroyed faster than the body can produce new ones. This can result from autoimmune conditions such as systemic lupus erythematosus, or some types of cancer such as lymphoma, or the use of medications that can destroy red blood cells (for example, methyldopa). While symptoms are similar to those of other types of anaemia, some people can experience a ‘haemolytic crisis’ where blood cells are destroyed rapidly and suddenly, resulting in fever, chills, back and stomach pain and a sudden significant drop in blood pressure.

Pernicious anaemia, caused by the intestine’s inability to adequately absorb vitamin B12 from food. Because a deficiency of vitamin B12 can lead to damage to the nervous system, a person with pernicious anaemia must take B12 supplements for life. These are usually given by injection, but research suggests oral treatment may be as effective.

Folic acid deficiency anaemia, caused by a lack of folic acid (folate) in the diet. Folate is found in green, leafy vegetables, fresh fruit and meat. Because the body stores only a small amount of folate, a person who doesn’t eat much of these foods may develop a deficiency within a few months. Treatment consists of rectifying the diet and taking supplements if needed.

Bone marrow failure, which may be due to leukaemia or other cancer-like diseases infiltrating the bone marrow and affecting the production of red cells. Some medicines and treatments, such as chemotherapy agents or radiotherapy, can also affect the bone marrow’s ability to produce red cells.

Anaemia of chronic disease — it is common for people with significant chronic (longstanding) disease of any sort (for example, kidney failure) to have mild anaemia.

Aplastic anaemia — a defect in red blood cell production by the bone marrow (white cell and platelet production is also affected). Some cases have no known cause but others result from problems with the immune system.

Sickle cell anaemia and thalassaemia — disorders of haemoglobin. Sickle-cell anaemia is characterised by abnormally shaped red blood cells which block and damage small blood vessels, causing blocked blood vessels and eventually organ damage. It is more common in black people than Caucasians. Thalassaemias are a range of genetic disorders resulting from errors in the production of the amino acids that make up haemoglobin: anaemia is a common symptom of these disorders.

How do I know if I have it?

Your doctor can give you a range of simple blood tests that will allow the exact cause of your anaemia to be identified.

Prevention and treatment of anaemia

If you have anaemia your treatment will depend on its cause.

If you are deficient in iron, your doctor may recommend a supplement. You can buy these from a health food store or pharmacy.