What is anaemia?
Red blood cells contain haemoglobin, which is the molecule that carries oxygen in the blood. The red cells travel through the lungs where the haemoglobin becomes oxygenated (picks up oxygen) and bright red in colour. The red cells are then pumped by the heart to the rest of the body where the haemoglobin gives up its oxygen to the tissues and becomes dark blue in the process.
‘Anaemia’ means that the level of red cells, and therefore of haemoglobin, in the blood is abnormally low. As a result the oxygen-carrying capacity of blood is reduced. Anaemia may be caused by excessive bleeding, by destruction of red cells or by decreased production of red cells. Anaemia caused by decreased production of red blood cells is discussed here. Anaemia from excessive bleeding is discussed in a separate Factsheet.
What causes anaemia and who is at risk?
Decreased production of red cells is mainly caused by:
- not enough iron (iron deficiency),
- vitamin B12 deficiency, or
- folic acid (a vitamin, also called folate) deficiency.
For red blood cells to be produced by the bone marrow, many nutrients are needed, such as iron, vitamin B12 and folic acid. These are taken in by the body from food, and iron is also recycled from red cells that have died. Except for infants, a diet deficient in iron (which is predominantly found in red meat) does not cause anaemia. Generally, the only cause of iron-deficiency anaemia is chronic (prolonged) bleeding, during which the body’s supply of recycled iron is too low and the shortfall cannot be made up by the diet. Menstrual bleeding is the most common cause of iron-deficiency anaemia in women before the menopause, but after this and in men it is usually caused by bleeding from somewhere in the gut, such as a polyp (a benign growth), cancer of the large bowel or a peptic ulcer.
Chronic (prolonged) diseases, such as infections, rheumatoid arthritis and cancer, can cause iron-deficiency anaemia because the developing red cells in the bone marrow are unable to use the iron stores.
Red blood cells also need vitamin B12 and folic acid to mature. If either is lacking then an anaemia called ‘megaloblastic anaemia’ develops in which the red cells are large and abnormal (called ‘megaloblast cells’). The main cause of vitamin B12 deficiency anaemia is ‘pernicious anaemia’, in which there is inadequate absorption of vitamin B12 from the diet (mainly from meat and some vegetables).
Vitamin B12 binds a protein called intrinsic factor which is produced in the stomach; this complex of vitamin B12 and intrinsic factor travels to the small bowel where it is absorbed into the blood stream. Without intrinsic factor, vitamin B12 cannot be absorbed; in pernicious anaemia, the stomach does not produce intrinsic factor and so vitamin B12 is not absorbed, however much is taken in the diet.
This anaemia can often take more than two years to develop because there are large stores of vitamin B12 in the liver. In some diseases of the small bowel, such as Crohn’s disease, vitamin B12 absorption can be impaired. A strict vegetarian diet can also cause vitamin B12 deficiency.
A lack of folic acid, which is more common in the Western world than lack of vitamin B12, also leads to megaloblastic anaemia. The main cause is a diet poor in folic acid, which is mainly found in fresh fruit and raw vegetables. Reduced uptake of folic acid can be caused by excessive alcohol consumption and by certain medicines.
Some drugs used to treat cancer also cause megaloblastic anaemia.
What are the common symptoms and complications of anaemia?
The symptoms of anaemia include:
- dizziness (especially when standing), and
- a weak, rapid pulse.
Iron deficiency also causes:
- inflammation of the tongue,
- cracks at the sides of the mouth,
- deformities of the fingernails, and
- pica (a craving for earth, ice or other non-foods).
Vitamin B12 deficiency also causes:
- damage to nerves (abnormal sensation and movement),
- sore tongue,
- pigmented skin,
- colour blindness, and
- depression, confusion and decreased intellectual function.
Folic acid deficiency also causes:
- foetal malformations (including spina bifida) and
- neurological abnormalities in infants.
How do doctors recognise anaemia?
Anaemia is identified by blood tests to measure the number of red blood cells and the amount of haemoglobin in the blood. Iron, vitamin B12 and folic acid levels can be measured and megaloblast cells can also be seen under the microscope. The source of bleeding is usually investigated in iron-deficiency anaemia and other more involved tests can be done to check vitamin B12 uptake for pernicious anaemia.
What is the treatment for anaemia?
Self-care action plan
A varied diet should be followed. If you are a meat-eater, make sure you eat plenty of raw vegetables and fruit. If you are a strict vegetarian, you should consider vitamin B12 supplements to prevent the possibility of permanent neurological damage. Pregnant women should take iron and folic acid supplements because of the increased needs of the baby. Indeed, women should take folic acid before conception.
Iron-deficiency anaemia is treated by stopping any bleeding, which may necessitate surgery and/or medicines for conditions such as peptic ulcer or excessive blood loss from menstruation. Iron supplements are also given; they may cause constipation and turn the stools black (this is harmless). Iron supplements do not help the anaemia of chronic disease and doctors usually try to treat the underlying condition. Vitamin B12 deficiency is usually treated with life-long monthly injections of vitamin B12 because poor absorption when taken by mouth is usually the problem. Folic acid deficiency is usually treated with folic acid tablets or syrup.
What is the outcome of anaemia?
Most types of anaemia are easily treated with appropriate supplements. If bleeding is the cause of iron-deficiency anaemia, the outcome depends on the underlying cause, as is the case with anaemia of chronic disease.