Vitamin B12: function, foods, deficiency and supplements

Find out all about vitamin B12 (cyanocobalamin), including what it does, how much you need, where to find it and who might need to supplement their diet

Overview

What is vitamin B12 and what does it do?

Like all the B vitamins, vitamin B12 (cynocobalamin) is needed to help your body convert food into energy. It’s also essential for:^1,2

• making red blood cells
• a healthy nervous system
• normal psychological function
• reducing tiredness and fatigue

Vitamin B12 is water-soluble, which means we need to eat enough every day. Our body can store a small amount of B12 in the liver,³ but we still have to get the right amount from our daily diet. However, vitamin B12 is only naturally found in animal products such as meat and dairy, so vegans and vegetarians are at risk of low intakes. Older people and others who don’t produce enough stomach acid to absorb B12 properly, may also be at risk of deficiency. Symptoms of a B12 deficiency include extreme fatigue, feeling weak and depression.⁴

Function of vitamin B12

What does vitamin B12 do in the body?

As part of the B-vitamin family, B12 helps release energy from the food we eat. But it’s also involved in:^5,6

• producing red blood cells
• normal nervous system function
• supporting the immune system
• maintaining healthy psychological function
• helping the body absorb folic acid
• fighting fatigue
• creating DNA during cell divisions

How much vitamin B12 do I need?

All adults need 1.5mcg of vitamin B12 every day.⁷ You should be able to get this from eating a well-balanced diet, but you’re more at risk of a vitamin B12 deficiency  if you don’t eat meat or animal products.

Breast-feeding mothers may need an extra 0.5mcg a day, particularly if they’re also vegetarian or vegan.⁸

Do children need vitamin B12?

Vitamin B12 is needed for healthy cell division,⁹ so it’s important for growing children:

• 1-3 years old – 0.5mcg a day
• 4-6 years – 0.8mcg a day
• 7-10 years – 1mcg a day
• 11-14 years – 1.2mcg a day
• 15-18 years – 1.5mcg a day¹⁰

Vitamin B12 foods

Which foods are the best sources of vitamin B12?

The richest sources of B12 are animal-based, including:¹¹

• meat and liver
• fish
• clams
• milk and dairy products
• eggs

Plant-based sources of vitamin B12 include:¹²

• yeast extract
• fortified plant milks
• fortified breakfast cereals
• soya foods fortified with B12

The synthetic (man-made) version of B12 is called cyanocobalamin, which you may see in supplements.

Vitamin B12 deficiency

What are the symptoms of vitamin B12 deficiency?

A lack of vitamin B12 can lead to megaloblastic anaemia; your body produces fewer red blood cells, which are also larger than normal.¹³ Symptoms of a B12 deficiency¹⁴ include:

• fatigue/exhaustion
• muscle weakness
• vision problems
• pins and needles
• sore tongue or mouth ulcers
• issues with memory
• depression

A vitamin B12 deficiency is most likely to affect vegetarians or vegans, and older people. Vegans and vegetarians are at risk because they don’t eat meat, while older people may not absorb vitamin B12 properly from their food due to declining levels of stomach acid.¹⁵

What happens if I consume too much vitamin B12?

There’s no set upper limit for vitamin B12, as there is very little evidence that too much is harmful.¹⁶ But the NHS advises having no more than 2mcg a day.¹⁷

Vitamin B12 supplements

When should I take vitamin B12 supplement?

If you’re following a plant-based diet, taking a vitamin B12 supplement can help prevent a deficiency. Breast-feeding mothers could also consider a supplement, as they need an extra 0.5mcg a day.¹⁸ Older people, or those taking medication to reduce production of stomach acid, may need a B12 supplement to boost absorption.¹⁹

Should children take a vitamin B12 supplement?

Unless your child is vegan or vegetarian, there’s no need for them to take a B12 supplement.

Should women take a vitamin B12 supplement during pregnancy?

No – if you eat meat, you’ll get all the B12 you need. If you’re vegetarian or vegan, talk to your GP before deciding to take any supplements.

What are the potential benefits of taking vitamin B12 supplements?

Homocysteine, a type of amino acid, has been linked to heart disease due to its negative effects on arteries.²⁰ But a 2010 study found that people taking vitamin B12 supplements had lower homocysteine levels.²¹ It may also help protect against osteoporosis. US researchers reported that people with low vitamin B12 levels also had lower than normal levels of bone mineral density.²² Shop Vitamins Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies. By Rosalind Ryan on December 7, 2018 Reviewed by dietititan & nutritionist Azmina Govindji on December 10, 2018

Sources
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3. Vegetarian Society. Vitamin B12. Available from: https://www.vegsoc.org/B12
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5. Nic Fleming. The Guardian. Everything you need to know about vitamin B12 deficiency. Available from: https://www.theguardian.com/lifeandstyle/2017/feb/28/everything-need-to-know-about-vitamin-b12-deficiency-immune-system
6. O’Leary F, Samman S. Vitamin B12 in health and disease. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257642/
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8. Expert Group on Vitamins and Minerals. Safe Upper Limits for Vitamins and Minerals. Available from: https://cot.food.gov.uk/sites/default/files/vitmin2003.pdf
9. As Source 6
10. Public Health England. Government Dietary Recommendations. Available from: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/618167/government_dietary_recommendations.pdf
11. National Institutes of Health. Vitamin B12. Available from: https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/
12. As Source 3
13. Healthline. Megaloblastic Anaemia. Available from: https://www.healthline.com/health/megaloblastic-anemia
14. As Source 4
15. British Nutrition Foundation. Vitamin B12 (cyanocobalamin). Available from: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/vitamins.html?limit=1&start=10
16. As Source 8
17. As Source 1
18. As Source 8
19. Andrès E, et al. Vitamin B12 (cobalamin) deficiency in elderly patients. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC490077/
20. Ganguly P, Alam SF. Role of homocysteine in the development of cardiovascular disease. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326479/
21. Armitage JM, et al. Effects of homocysteine-lowering with folic acid plus vitamin B12 vs placebo on mortality and major morbidity in myocardial infarction survivors: a randomized trial. Available from: https://www.ncbi.nlm.nih.gov/pubmed/20571015

22. Tucker KL, et al. Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Study. Available from: https://www.ncbi.nlm.nih.gov/pubmed/15619681