In order to bring you the best possible user experience, this site uses Javascript. If you are seeing this message, it is likely that the Javascript option in your browser is disabled. For optimal viewing of this site, please ensure that Javascript is enabled for your browser.

Vitamin B12-deficiency anaemia

Anaemia is when there are too few red blood cells or not enough haemoglobin in the blood. Vitamin B12-deficiency anaemia is caused when there isn’t enough vitamin B12 in the body.

You need vitamin B12 for many important body processes, particularly for making red blood cells and keeping your nerves healthy. If it’s in short supply, your body won't make as many red blood cells; they will be abnormally large and won't last for as long as they should. If you don’t have enough red blood cells, your tissues and organs may not get enough oxygen. This leads to the symptoms of anaemia.

Symptoms of vitamin B12-deficiency anaemia 

The symptoms of vitamin B12-deficiency anaemia include:

  • feeling very tired
  • breathlessness even after little exercise
  • heart palpitations
  • headaches
  • a reduced appetite
  • a sore mouth and tongue.

If you have vitamin B12-deficiency anaemia, you may also look pale or jaundiced (have a yellowy tinge to your skin and the whites of your eyes).

As well as the symptoms of anaemia, vitamin B12-deficiency may cause symptoms related to your nerves. This is called vitamin B12 neuropathy. It may affect your movement and sensation, especially in your legs, cause numbness or pins and needles and decrease your sensitivity to touch, vibration or pain. It can also cause confusion, depression, poor concentration and forgetfulness.

These symptoms aren't always due to vitamin B12-deficiency anaemia, but if you have them see your GP.

Complications of vitamin B12-deficiency anaemia 

If vitamin B12-deficiency anaemia isn't treated, there’s a range of possible complications. For example, it can affect your movement and co-ordination. It can also put you at risk of heart problems. Talk to your GP for more information.

Causes of vitamin B12-deficiency anaemia 

Pernicious anaemia

Pernicious anaemia is the most common cause of vitamin B12-deficiency anaemia. It develops if your body can't absorb vitamin B12 from food as it normally would.

Pernicious anaemia is an autoimmune disease, caused by antibodies from your immune system attacking your own body tissue, which it mistakes as being foreign. This causes inflammation in the lining of your stomach.

Normally, a protein known as intrinsic factor, which is made in your stomach, attaches to the vitamin B12 released from the food you have eaten and then carries the vitamin through your bowel wall into your blood. If you have pernicious anaemia, the stomach cells that produce intrinsic factor may be damaged, meaning vitamin B12 can no longer be absorbed and a deficiency develops, leading to anaemia.

The exact reasons why you may develop pernicious anaemia aren't fully understood at present. It tends to run in families and is most common in people over 60. It affects women more than men. If you have another autoimmune disease, such as Addison's disease, you may be more likely to develop pernicious anaemia.

Other causes

Other, less common, causes of vitamin B12-deficiency anaemia include:

  • Diet. Not getting enough vitamin B12 in your diet can cause vitamin B12-deficiency anaemia. This is rare in Western countries because this vitamin is normally stored in the liver and most of us have a supply that lasts for some years. But strict vegans may be at risk because their diet excludes meat and animal products which are the foods that provide this vitamin. If you don’t eat meat but do eat dairy products, you should be getting enough vitamin B12. If you are vegan, make sure that you include foods fortified with vitamin B12, and you may also want to take a regular supplement.
  • Inflammatory bowel diseases. Conditions that affect the small bowel, such as Crohn’s disease, can interfere with vitamin B12 absorption.
  • Surgery. Any kind of surgery that removes part of or all of your stomach can cause vitamin B12-deficiency anaemia because intrinsic factor is produced in the stomach.
  • Liver disorders. These can reduce your body's ability to use or store vitamin B12.
  • Parasites. Parasitic infestation or too much bacteria in your bowel can interfere with the absorption of vitamin B12.

Diagnosis of vitamin B12-deficiency anaemia 

Your GP will ask about your symptoms, examine you and may also ask you about your medical history.

You may be asked to have a blood test. This includes a full blood count (FBC) that will give information about your haemoglobin levels (the oxygen carrying pigment in blood) and how many of each of the different types of blood cells you have. An FBC will also give information about the size of your red cells and the amount of haemoglobin each one contains.

If you have low levels of vitamin B12, you may need to have a test for the antibodies that cause pernicious anaemia.

Your GP may refer you to a haematologist (a doctor who specialises in treating blood disorders) to have further tests. This may include a biopsy (surgical removal of a small amount of tissue to examine your bone marrow).

Treating vitamin B12-deficiency anaemia 

Your GP will first try to identify why you're deficient in vitamin B12 so that the cause can be treated. If you don't get enough vitamin B12 in your diet for example, you may be referred to an accredited practising dietitian for advice on how to improve your vitamin B12 intake.

Vitamin B12-deficiency anaemia is usually treated with vitamin B12 supplementation. This will begin with a course of injections, for example once a week for six weeks. After this, you may need repeated doses every three months or so. If you have pernicious anaemia, you’ll need to have injections for the rest of your life.

Vitamin B12 injections can sometimes cause bruising and soreness at the site of injection. Other side-effects include feeling sick, headaches and dizziness, but these are rare.

Your GP will monitor you to check that your treatment is working. Shortly after you start, you’ll be asked to have a blood test to check that it's starting to have a beneficial effect. You’ll then need another blood test after about eight weeks to confirm that your haemoglobin and red blood cell levels have returned to normal.

Prevention of vitamin B12-deficiency anaemia 

You only need a small amount of vitamin B12 each day – about 2.4 micrograms daily according to the Medical Health and Research Council. If you eat a healthy well-balanced diet and don't have a condition that affects your absorption of vitamin B12 (see Causes of vitamin B12 anaemia above) you're unlikely to have a shortage.

Good sources of vitamin B12 include meat and other animal products such as eggs and cheese. Some breakfast cereals are fortified with vitamin B12. This means that vitamin B12 has been added during manufacturing.

If you eat a vegetarian or vegan diet, it can be difficult for you to get enough vitamin B12 because it isn't found in fruit, vegetables or grains. Try to include foods fortified with vitamin B12. Yeast products such as Marmite (but not Vegemite) are also good sources of vitamin B12 and can be used by vegetarians. Your GP may suggest that you take regular vitamin B12 supplements to prevent anaemia.

Further information 

Dietitians Association of Australia

Food Standards Australia New Zealand


Australian Red Cross Blood Service. Why haemoglobin and iron are important. [online] Sept 2010 [Accessed 1 Jul 2011] Sourced from:

Clinical Knowledge Summaries. Anaemia – vitamin B12 and folate deficiency. [online] London: National Institutes for Health and Clinical Excellence. 2007 [last updated Jan 2011, accessed 1 Jul 2011] Available from:

Food Standards Australia New Zealand. Spread, yeast, marmite. [online] 2010 [accessed 4 Jul 2011] Available from:

Food Standards Australia New Zealand. Spread, yeast, vegemite. [online] 2010 [accessed 4 Jul 2011] Available from:

Merck Manuals Online Medical Dictionary. Vitamin B12. [online] Whitehouse Station, NJ: Merck, Sharp and Dohme Corp. [Last updated Apr 2007, accessed 1 Jul 2011] Available from:

National Health & Medical Research Council. Nutrient Reference Values – Vitamin B12. [online] Canberra, ACT: Commonwealth of Australia. c2009 [accessed 1 Jul 2011] Available from:

National Institute for Health and Clinical Excellence (NICE). Anaemia management in chronic kidney disease: full guideline. [online] 2006 [Accessed 1 Jul 2011] Available from:

Last published: 30 July 2011

This information has been developed and reviewed for Bupa by health professionals. To the best of their knowledge it is current and based on reputable sources of medical research. It should be used as a guide only and should not be relied upon as a substitute for professional medical or other health professional advice.

Bupa Australia Pty Ltd makes no warranties or representations regarding the completeness or accuracy of the information. Bupa Australia is not liable for any loss or damage you suffer arising out of the use of or reliance on the information. Except that which cannot be excluded by law. We recommend that you consult your doctor or other qualified health professional if you have questions or concerns about your health. For more details on how we produce our health content, visit the About our health information page.