What Is Vitamin B12? Functions, Food Sources and Deficiency

Vitamin B12, also called cobalamin, is a water-soluble vitamin that helps the body make red blood cells, maintain a healthy nervous system, release energy from food and use folate. A lack of Vitamin B12 can lead to deficiency anaemia and may also affect the nervous system. (NHS: B vitamins and folic acid)

Most people can obtain Vitamin B12 from a varied diet, but dietary intake is only part of the picture. Some people have difficulty absorbing B12, and possible deficiency should be assessed by a healthcare professional rather than diagnosed from symptoms alone.

What does Vitamin B12 do?

Vitamin B12 supports several normal processes in the body. In particular, it helps with:

• normal red blood cell formation;
• normal function of the nervous system;
• releasing energy from food;
• the body’s use of folate.

Vitamin B12 is also involved in DNA synthesis and normal cell processes. These are essential functions, but they do not mean that taking more B12 than you need will automatically provide extra energy, improve memory or treat a health condition. (NHS; NIH Office of Dietary Supplements)

How much Vitamin B12 do UK adults need?

The NHS says adults aged 19 to 64 need about 1.5 micrograms of Vitamin B12 a day. Many people who regularly eat meat, fish, eggs or dairy products can obtain enough through food. Individual needs and the ability to absorb B12 can vary, so a reference amount is not a personal treatment recommendation. (NHS)

Which foods contain Vitamin B12?

Common food sources include:

• meat;
• fish;
• milk and other dairy products;
• eggs;
• foods fortified with Vitamin B12, such as some breakfast cereals and plant-based products.

Vitamin B12 is not naturally present in fruit, vegetables or grains. People following a vegan diet therefore need reliable fortified foods or other appropriate advice to meet their needs. Check food labels because the amount added varies between products. (NHS)

Who may be at greater risk of low Vitamin B12?

Low B12 is not always caused by diet. Possible risk factors include:

• following a vegan diet without reliable fortified foods or supplementation;
• pernicious anaemia, which affects the body’s ability to absorb B12;
• conditions or surgery that affect the stomach or intestines;
• some medicines that interfere with absorption;
• increasing age, because absorption can become less efficient.

NICE guidance covers recognising, diagnosing and managing B12 deficiency in people aged 16 and over. A clinician considers symptoms, medical history, risk factors and suitable tests together rather than relying on one online checklist. (NICE NG239; NHS deficiency overview)

What are the possible signs of Vitamin B12 deficiency?

Possible symptoms can include extreme tiredness, low energy, pins and needles, muscle weakness, a sore or red tongue, mouth ulcers, vision problems, and difficulties with memory or concentration. These symptoms can have many causes and do not confirm a B12 deficiency. (NHS)

If you think you may be deficient, speak to a GP. Prompt assessment matters because some problems associated with prolonged deficiency can become difficult to reverse. Seek professional advice rather than changing an existing treatment plan based on an article or online questionnaire.

How is possible deficiency checked?

A healthcare professional may consider your symptoms, diet, medicines and medical history before arranging suitable blood tests. Test interpretation is not always straightforward, and results need to be considered in context. NICE provides current UK guidance for clinicians on diagnosis and management. (NICE NG239)

Ampavit’s Vitamin B12 Deficiency Risk Assessment can help you organise possible risk factors before speaking to a professional, but it cannot diagnose deficiency or recommend treatment.

What are the different forms of Vitamin B12?

“Vitamin B12” is a family of compounds called cobalamins. Forms used in foods, supplements or clinical settings include cyanocobalamin, methylcobalamin and hydroxocobalamin.

Methylcobalamin is one metabolically active form. Cyanocobalamin and hydroxocobalamin are converted into active forms in the body. According to the NIH Office of Dietary Supplements, current evidence does not show that absorption rates from supplements differ by form. The most suitable form depends on the product, the reason it is being considered and professional advice—not on a universal claim that one form is best for everyone. (NIH Office of Dietary Supplements)

For a more focused explanation, read Ampavit’s guide to methylcobalamin.

Food, supplements and medical treatment are not interchangeable

A person with adequate absorption may be able to meet normal needs through food. Someone with a diagnosed deficiency may need a different approach depending on its cause. The NHS explains that treatment can involve tablets or clinician-administered medicine, and that the choice depends on whether the deficiency is diet-related and whether there are neurological concerns. (NHS treatment overview)

Do not use general product information as a substitute for diagnosis or personalised medical advice. If you are pregnant, breastfeeding, taking medicines or managing a medical condition, discuss supplements with an appropriate healthcare professional.