What is vitamin B12?

What are the symptoms of vitamin B12 deficiency, which foods can boost intake, and when should you consider a supplement? Find out with our expert guide.

What is vitamin B12?

Vitamin B12 – also known as cobalamin, is synthesised by bacteria. It is involved in many vital processes in the body, including:

  • Producing red blood cells
  • Keeping the nervous system healthy
  • Releasing energy from food
  • Creating DNA and RNA (the building blocks of every cell in the body)

Which foods contain vitamin B12?

Vitamin B12 is mainly found in meat, offal, milk, fish and eggs. The richest sources are liver, clams, kidneys and oysters.

For vegetarians and vegans, it is harder to obtain vitamin B12. It is found in some fermented foods, such as tempeh and more commonly in nori and nutritional yeast (or yeast extract like Marmite). Alternatively look out for vegan and vegatarian foods that are fortified with vitamin B12, such as some soya milks and breakfast cereals. Supplements are produced by a synthetic form of B12 and are widely available.

There is some evidence to suggest that the form and bioavailability of B12 found in vegetarian/vegan sources is not as able to meet our body’s requirements as animal sources. Those with a reduced intake of animal foods should speak to their GP or health professional in order to determine whether they should consider taking a supplement.

How much vitamin B12 you should eat per day?

Vitamin B12 is necessary in only very small amounts each day. The NHS advises that the recommended daily amount (RDA) is 1.5 micrograms (mcg) for adults.

How much of each food do you need to reach these amounts?

Most people will be able to meet their vitamin B12 needs through a balanced and varied diet. Some excellent food sources of vitamin B12 include:

100g clams = 99mcg
100g beef liver = 83mcg
100g mackerel = 19mcg
100ml soya milk = 2.4mcg
200g yogurt = 1.5mcg

Other good sources include most meats, salmon, cod, milk, cheese, eggs and fortified breakfast cereals.

What are the symptoms of a vitamin B12 deficiency?

Vitamin B12 deficiency is quite hard to detect and so can go undiagnosed for years. Symptoms can include fatigue, lethargy, shortness of breath, pale skin (possible with a pale yellow tinge), mouth ulcers, sensations of 'pins and needles', disturbed vision, impaired mental function and depression. Many of these symptoms are not unique to vitamin B12 deficiency, and not everyone who is diagnosed will experience these symptoms. If you are concerned that you may be deficient you should see your GP, who may wish to carry out a blood test.

A more severe form of vitamin B12 deficiency is called pernicious anaemia. This is an autoimmune disease which occurs due to issues with a specific glycoprotein called intrinsic factor (IF), which is created in the stomach and is necessary to absorb vitamin B12. Pernicious anaemia causes the immune system to attack the cells in the stomach which produce IF. Without IF, vitamin B12 cannot be absorbed and therefore deficiency can occur. Pernicious anaemia is now treated with B12 injections.

Read more from the NHS about vitamin B12 or folate deficiency anaemia and pernicious anaemia.

Who might be at risk of a vitamin B12 deficiency?

Anyone who is unable to eat a varied and balanced diet, including the elderly, may be more at risk of B12 deficiency. Additionally, people with certain medical conditions, such as coeliac disease and Crohn's disease, may be unable to absorb adequate B12 from food.

Strict vegans who do not include any fish, poultry, eggs or dairy products in their diet and are not taking vitamin B12 supplements are at increased risk of deficiency. For those eating an exclusively plant-based diet, it is recommended to get B12 levels checked regularly. Vegetarians who do not regularly include dairy in their diet may also be at risk and should see their GP if they are concerned.

Women who are pregnant or breastfeeding should consult their GP for guidance if they are concerned that they may be deficient in vitamin B12.

Anyone considering taking a B12 supplement should talk to their GP or associated health professional first. 

Recipe suggestions

Liver & bacon with onion gravy 
Warm mackerel & beetroot salad 
Vegan tomato & mushroom pancakes 


This article was published on 30th March 2017.

Jo Lewin works as a Community Nutritionist and private consultant. She is a Registered Nutritionist (Public Health) registered with the UKVRN. Visit her website at www.nutrijo.co.uk or follow her on Twitter @nutri_jo.

All health content on bbcgoodfood.com is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact  your local health care provider. See our website terms and conditions for more information.

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