Introduction 

Vitamin B12 or B9 (commonly called folate) deficiency anaemia occurs when a lack of vitamin B12 or folate causes the body to produce abnormally large red blood cells that cannot function properly.

Red blood cells carry oxygen around the body using a substance called haemoglobin.

Anaemia is the general term for having either fewer red blood cells than normal or having an abnormally low amount of haemoglobin in each red blood cell.

There are several different types of anaemia, and each one has a different cause. For example, a common form of anaemia is iron deficiency anaemia, which occurs when the body does not contain enough iron.

This topic focuses on anaemia caused by a lack of vitamin B12 or folate in the body.

Signs and symptoms

Vitamin B12 and folate perform several important functions in the body, including keeping the nervous system healthy.

A deficiency in either of these vitamins can cause a wide range of problems, including:

Some of these problems can also occur if you have a deficiency in vitamin B12 or folate, but do not have anaemia.

Read more about the symptoms of vitamin B12 deficiency or folate deficiency anaemia.

When to see your GP

You should see your GP if you think you may have a vitamin B12 or folate deficiency. These conditions can often be diagnosed based on your symptoms and the results of a blood test.

It's important for vitamin B12 or folate deficiency anaemia to be diagnosed and treated as soon as possible because, although many of the symptoms will improve with treatment, some problems caused by the condition can be irreversible.

Read more about diagnosing vitamin B12 or folate deficiency anaemia.

What can cause a vitamin B12 or folate deficiency?

There are a number of problems that can lead to a vitamin B12 or folate deficiency, including:

  • pernicious anaemia  where your immune system attacks healthy cells in your stomach, preventing your body from absorbing vitamin B12 from the food you eat; this is the most common cause of vitamin B12 deficiency in the UK.
  • a lack of these vitamins in your diet  this is uncommon, but can occur if you have a vegan diet, follow a fad diet or have a generally poor diet for a long time
  • medication – certain medications, including anticonvulsants and proton pump inhibitors (PPIs), can affect how much of these vitamins your body absorbs 

Both vitamin B12 deficiency and folate deficiency are more common in older people, affecting around 1 in 10 people aged 75 or over, and 1 in 20 people aged 65 to 74.

Read more about the causes of vitamin B12 or folate deficiency anaemia.

How vitamin B12 or folate deficiency anaemia is treated

Most cases of vitamin B12 and folate deficiency can be easily treated with injections or tablets to replace the vitamin you are deficient in.

Vitamin B12 supplements are usually given by injection at first. Then, depending on whether your B12 deficiency is related to your diet, you will either require B12 tablets between meals or regular injections. These treatments may be needed for the rest of your life.

Folic acid tablets are used to restore folate levels. These usually need to be taken for four months.

In some cases, improving your diet can help treat the condition and prevent it recurring. Vitamin B12 is found in meat, fish, eggs, dairy products, yeast extract (such as Marmite) and specially fortified foods. The best sources of folate include green vegetables such as broccoli, Brussels sprouts and peas.

Read more about treating vitamin B12 or folate deficiency.

Further problems

Although it is uncommon, vitamin B12 or folate deficiency (with or without anaemia) can lead to complications, particularly if you've been deficient in vitamin B12 or folate for some time.

Potential complications can include problems with the nervous system, temporary infertility, heart conditions, pregnancy complications and birth defects.  

Some complications will improve with appropriate treatment, but others  such as problems with the nervous system – can be permanent. 

Read more about the complications of vitamin B12 or folate deficiency anaemia.

Vitamin B12 or folate deficiency anaemia can cause the body to produce abnormally large red blood cells  

Page last reviewed: 21/05/2014

Next review due: 21/05/2016