Megaloblastic Anaemia

A type of anaemia caused by a lack of vitamin B12 or folic acid

  • More common over the age of 40
  • Gender, genetics, and lifestyle as risk factors depend on the cause

Two major vitamins, B12 and folic acid, play an essential role in the production of healthy red blood cells. Deficiency of either vitamin may lead to megaloblastic anaemia, in which large, abnormal red blood cells (megalo-blasts) are produced by the bone marrow, and the production of normal red blood cells is reduced. The blood may thus be unable to carry sufficient oxygen to the tissues.

What are the causes?

Lack of vitamin B12 is often due to an autoimmune disorder in which antibodies are produced that damage the stomach lining and prevent it from forming intrinsic factor, which is essential for the absorption of vitamin B12 from food in the intestines. This type of megaloblastic anaemia, called pernicious anaemia, tends to run in families and is more common in women and in people with other autoimmune disorders, such as Hashimoto’s thyroiditis (see Thyroiditis). Intestinal disorders, such as coeliac disease, or abdominal surgery can also interfere with vitamin B12 absorption. Because vitamin B12 occurs naturally only in foods of animal origin, vegans are at risk of deficiency and, therefore, of developing megaloblastic anaemia unless they take supplementary vitamin B12.

Folic acid deficiency is often due to a poor diet. People who abuse alcohol are at particular risk because alcohol interferes with the absorption of folic acid in the intestines. Pregnant women may also be at risk of deficiency because folic acid requirements are higher in pregnancy. Disorders causing a rapid turnover of cells, including severe psoriasis, may also cause folic acid deficiency. In rare cases, the deficiency is a side effect of certain drugs, such as anticonvulsants and anticancer drugs.

What are the symptoms?

The initial symptoms of megaloblastic anaemia, which are common to all anaemias, develop slowly and may include:

  • Tiredness and a feeling of faintness.

  • Pale skin.

  • Shortness of breath on mild exertion.

These symptoms of megaloblastic anaemia may worsen over time. Although lack of folic acid does not produce additional symptoms, lack of vitamin B12 may eventually damage the nervous system, possibly leading to:

  • Tingling in the hands and feet.

  • Weakness and loss of balance.

  • Loss of memory and confusion.

People who have pernicious anaemia may also notice a yellow tinge to their skin due to jaundice.

What might be done?

The diagnosis requires blood tests to look for megaloblasts and to measure the levels of vitamin B12, folic acid, and iron. You may also have a bone marrow aspiration and biopsy to obtain tissue samples for further examination.

Megaloblastic anaemia caused by an inability to absorb vitamin B12 may be improved by treating the underlying disorder, but some people, such as those who have pernicious anaemia and malabsorption caused by surgery, require lifelong regular injections of vitamin B12 (see Vitamins). Symptoms should subside within days, but existing damage to the nervous system may be irreversible.

If megaloblastic anaemia is caused by dietary deficiency, the condition usually disappears with an improved diet. Vegans may need to take vitamin B12 supplements.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

Back to top