Pernicious anaemia

Also known as vitamin B12 deficiency

Key points about pernicious anaemia

  • Pernicious anaemia occurs when your body doesn’t have enough vitamin B12 to make red blood cells.
  • This may be caused by an autoimmune condition, digestive difficulties or not getting enough vitamin B12 in your diet.
  • Treatment with vitamin B12 injections is key to preventing serious health issues.


Foods containing Vitamin B12 on a table
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  • Most people absorb vitamin B12 from food such as eggs, diary and meat. Vitamin B12 is essential for your body to create new red blood cells, which carry oxygen around your body. It also has a role in helping your nerves and brain function.
  • Pernicious anaemia is an autoimmune condition where your immune system attacks cells in your stomach that make a protein called intrinsic factor. Intrinsic factor is needed for your body to absorb vitamin B12 from the food you eat. 
  • Without enough vitamin B12, you can feel tired, weak and lethargic. Over time, a lack of vitamin B12 can lead to serious health problems.
  • Treatment involves vitamin B12 injections.

What causes pernicious anaemia?

In pernicious anaemia, your body can't make enough healthy red blood cells because it doesn't have enough vitamin B12. This is caused by a lack of intrinsic factor, a protein made in your stomach. Without enough vitamin B12, your red blood cells don't divide normally and can’t carry out their job of moving oxygen around your body.

Other causes of low vitamin B12 include:

  • digestive conditions, such as Crohn's disease and coeliac disease
  • surgery to remove parts of your bowel
  • some medicines that affect the absorption of vitamin B12, such as proton pump inhibitors
  • not getting enough B12 from your food, eg, from having a strict vegan diet.

Without enough red blood cells to carry oxygen to your body, you may feel tired and weak.

Other symptoms of low vitamin B12 include:

  • sore tongue or mouth ulcers
  • pins and needles or numbness
  • vision problems
  • unsteadiness
  • depression
  • confusion
  • memory problems.

Severe or long-lasting pernicious anaemia can damage your heart, brain and other organs. It can also cause other problems, such as nerve damage, memory loss and gut problems. You may also may be at higher risk for weakened bone strength and stomach cancer.

Pernicious anaemia usually develops over the age of 50. Women are more often affected than men and it tends to run in families. It occurs more often in people who have other autoimmune diseases.

Other than people born with a lack of intrinsic factor, other people most at risk of vitamin B12 deficiency include:

  • vegans who don't take a vitamin B12 supplement
  • breastfed infants of vegan mothers – these infants can develop anaemia within months of being born because they haven't had enough time to store vitamin B12 in their bodies
  • people who drink alcohol to excess
  • older adults or others who may not get enough nutrients in their diets
  • people with undiagnosed gastrointestinal disorders, such as Crohn’s disease or coeliac disease.

See your doctor if you have the symptoms listed above. A blood test can measure vitamin B12 levels. If it is low, further blood tests can check for the antibodies found in pernicious anaemia.

Treatment for pernicious anaemia is essential to avoid long-term damage to your organs. You will need vitamin B12 injections to replace then keep up your body stores of vitamin B12. Vitamin B12 injection is also called hydroxocobalamin. Usually at the start of treatment, the injections are given frequently over 2-3 weeks. This quickly builds up your body's store of vitamin B12. Thereafter, you will need vitamin B12 injections less often (every 2-3 months).

Vitamin B12 tablets are not usually recommended to treat pernicious anaemia because very little vitamin B12 is absorbed from the gut. Also, vitamin B12 tablets that have high-enough doses of vitamin B12 needed to treat pernicious anaemia are not easily available. Some pharmacies may have to order it in specifically for you. Note that vitamin B complex tablets do not contain any vitamin B12. 

Good food sources of vitamin B12 include:

  • meats such as beef, liver, poultry and fish
  • eggs and dairy products (such as milk, yoghurt and cheese)
  • foods fortified with vitamin B12, such as soy-based drinks and breakfast cereals.

Vitamin B12 deficiency(external link) NHS, UK, 2019
Eating well to prevent vitamin B12 deficiency(external link) HealthInfo, NZ, 2018
Vitamin B12 fact sheet for consumers(external link) National Institute of Health, US, 2016


  1. Pernicious anaemia(external link) National Heart, Lung & Blood Institute, US 
  2. Pernicious anaemia and vitamin B12 deficiency(external link) Patient Info, UK, 2016 


Vitamin B12 fact sheet for consumers

National Institute of Health, US, 2016

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Credits: Content shared between HealthInfo Canterbury, KidsHealth and Healthify He Puna Waiora as part of a National Health Content Hub Collaborative.

Reviewed by: Dr Helen Kenealy, geriatrician and general physician, Counties Manukau DHB

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