Emma has been a Registered Dietitian for over 17 years and has experience in adult and paediatric dietetics. She has been the Editor of NHD for seven years, steering the editorial content and supporting the production process. Emma currently works in industry.

Emma Coates, RD

Vitamin B12: the nutrient that can really get on your nerves... but that's ok!

Vitamin B12 is a nutrient we can’t live without. This essential vitamin is required to generate blood cells, for DNA synthesis and the myelination of nerves.(1,2) It contributes to normal functioning of the nervous system, but also plays a role in the health of the immune, cardiovascular and gastrointestinal systems.(2,3) It prevents the development of megaloblastic anaemia, where the body produces abnormally large red blood cells due to impaired DNA synthesis during cell production. This results in inadequate oxygen supply around the body.

Daily requirements vary throughout the lifespan, with healthy adults in the UK requiring 1.5ug per day.(4)

UK Vitamin B12 requirements (4)

0-1 years


1-3 years


4-6 years


7-10 years


11-14 years


15 years +



Vitamin B12 can be obtained from the diet predominantly from foods of animal origin, including meat, fish, milk and eggs.(5) Plant-based sources include some fortified breakfast cereals, soy products and plant milk drinks.(6)

Absorption of vitamin B12 is complex and relies on several parts of the gastrointestinal tract and the secretions that are produced along the way. For an overview of vitamin B12 digestion and absorption, take a look at this video here...


If there is inadequate intake, malabsorption, or low levels of vitamin B12 present in the body, deficiency occurs, impacting the function of multiple systems and resulting in a variety of symptoms.(3)

Common symptoms of deficiency include the following: (8-11)

  • Tiredness and fatigue
  • Lack of energy
  • Pale skin
  • Headaches
  • Shortness of breath
  • Feeling faint
  • Pins and needles
  • Muscle weakness
  • Problems with vision
  • Sore, red tongue (glossitis)
  • Loss of appetite
  • Diarrhoea
  • Weight loss
  • Psychological problems, which can include: depression, anxiety, confusion, memory problems, dementia
  • Reduced cutaneous sensation

If left untreated, vitamin B12 deficiency can lead to irreversible neurological damage, impact on fertility and the ability to conceive; it can increase the risk of neural tube defects if the patient is pregnant.(8) There is also an increased risk of stomach cancer if the cause of the deficiency
is autoimmune.(8)

The prevalence of vitamin B12 deficiency within the UK is not completely clear. However, it is estimated to affect around 6% of the adult population under the age of 60 years, which increases to around 20% in those over 60 years.(12)


The causes of vitamin B12 deficiency can vary and it can present in a wide range of patient groups. (2,12,13)

Dietary intake
Limited vitamin B12 consumption from the diet as a result of malnutrition, reduced animal product intake or a strict plant-based diet. Those who exclude animal products may be at risk of deficiency if adequate amounts of alternative non-animal sources are not consumed.

Gastric Atrophy (Atrophic Gastritis)
Chronic inflammation of the stomach lining can disrupt the production of intrinsic factor, which is required to utilise vitamin B12. Atrophic gastritis can develop as part of the ageing process or Helicobacter Pylori infection. It can be a consequence of autoimmune gastritis, where partial cells or intrinsic factor, or both are destroyed, both of which are required for the digestion and absorption of vitamin B12. In this case, pernicious anaemia is diagnosed.

Intestinal infection or disease Inflammatory bowel disease, pancreatitis, tapeworm, giardiasis, intestinal bacterial overgrowth, short bowel syndrome.
Chronic inflammation of the gastrointestinal tract or disruption to the gut flora can disturb the digestion and absorption of vitamin B12.

Surgical intervention Gastric bypass, partial gastrectomy, ileal resections, surgical anastomosis
Surgical intervention can interfere with or result in the removal of the gastrointestinal areas that are essential for the digestion and absorption of vitamin B12.

There are a wide variety of medications that can impact on vitamin B12 levels. These include – Metformin, proton pump inhibitors, oral contraceptives, Colchicine (to treat gout), Cimetidine (to treat gastric ulcers), Phenobarbital, Pregabalin, Primidone and Topiramate (to treat epilepsy).

Congenital/inherited disorders
Rare disorders that impact on the metabolism of vitamin B12.

Intrinsic factor receptor deficiency/defect - Imerslund Gräsback syndrome, Congenital deficiency of intrinsic factor - 'juvenile' pernicious anaemia, Cobalamin mutation (C-G-1 gene), Transcobalamin deficiency.

Other risks
Patient groups that are also at risk include those living with cancer, HIV/AIDS, liver disease, chronic alcoholism, those with autoimmune conditions such as Addison’s disease, thyroid disease, vitiligo. Lower vitamin B12 levels may be detected in pregnant women.


Folate deficiency can also cause megaloblastic anaemia, and symptoms can be very similar to those of vitamin B12 deficiency. Identifying the correct deficiency and providing appropriate treatment is vital to ensure that patients are managed effectively.(13) For example, where there is a combined low folate and B12 levels, tissue transglutaminase (TTG) levels should be checked (to exclude coeliac disease) regardless of the presence or absence of gastrointestinal symptoms of malabsorption.(13) For more information on folate deficiency and its management, visit Vitamin B12 or folate deficiency anaemia. (8)


NICE recommends the following:(14)

For those with neurological involvement - Initially a hydroxocobalamin 1mg intramuscular injection on alternate days until there is no further improvement, moving to hydroxocobalamin 1mg intramuscularly every two months.

For those with no neurological involvement - Initially a hydroxocobalamin 1mg intramuscular injection three times a week for two weeks. The maintenance dose depends on whether the deficiency is diet-related or not.

Not thought to be diet related - Hydroxocobalamin 1mg intramuscular injection every 2–3 months for life. Alternatively, daily large oral doses (500 to 1000 micrograms) can be considered for maintenance therapy.

Thought to be diet related - Either oral cyanocobalamin tablets 50–150 micrograms daily between meals, or have a twice-yearly hydroxocobalamin 1mg injection. In vegans, treatment may need to be life-long, whereas in other people with dietary deficiency replacement treatment can be stopped once the vitamin B12 levels have been corrected and the diet has improve.

For those where the vitamin B12 deficiency is thought to be diet-related, NICE also recommends providing this dietary advice: (14)

Encourage good sources of vitamin B12, for example:

  • Foods which have been fortified with vitamin B12 (for example some soy products, and some breakfast cereals and breads) are good alternative sources to meat, eggs, and dairy products
  • Milk and other dairy products
  • Salmon and cod


PA is an autoimmune disease caused by the impaired absorption of dietary vitamin B12 due to the atrophy of the gastric mucosa.(1) The atrophy leads to a reduction in parietal cells, which secrete intrinsic factor (IF), an essential substance for vitamin B12 absorption.(15) This means that absorption of dietary vitamin B12 is significantly inhibited and alternative supplementation is required. PA is not related to poor dietary intake of vitamin B12.

PA is the most common cause of vitamin B12 deficiency and megaloblastic anaemia.(16) It is more frequently diagnosed in women than men,(15) and usually affects people aged 40-70 years.(16) It’s estimated to affect 0.1% of the general population and 1.9% of those aged 60 years or above.(16)

The management of PA is provided via intramuscular injections of 1mg hydroxocobalamin every two to three months for life.(14)

Whilst there are NICE guidelines (14) to diagnose and manage PA, there are concerns regarding adequacy of diagnosing and treating the condition. A recent review concerning patient experiences of the diagnosis and treatment of PA and autoimmune gastritis highlighted significant gaps in understanding across the healthcare community.(17) It was also found that patients withdraw from seeking care due to delays in diagnosis and poor treatment protocols,(17) which is a concern given the potentially damaging effects of vitamin B12 deficiency.

Additionally, there are frequent and widespread concerns from patients regarding the current treatment regimen for PA.(18) A one-size-fits-all approach of a 1mg hydroxocobalamin injection every two to three months does not suit all patients. Whilst some people manage well on this amount over this timeframe, others struggle and may require more injections. However, due to the current NICE guidance,(14) many GPs are reluctant to deviate from the current recommendations. The Pernicious Anaemia Society has raised these concerns with the Department of Health and Social Care and have conducted research into this matter, working with clinic researchers to find solutions.


    1. Muhajir, M., et al. (2020) Pernicious anaemia. Pernicious anaemia | The BMJ
    2. Pernicious Anaemia Society (2023) What’s the difference between vitamin B12 deficiency and pernicious anaemia? The difference between B12 Deficiency and Pernicious Anaemia (pernicious-anaemia-society.org)
    3. Great Britain nutrition and health claims (NHC) register (2022) Vitamin B12. Great Britain nutrition and health claims (NHC) register - GOV.UK (www.gov.uk)
    4. COMA (1991) UK Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. pdf (publishing.service.gov.uk)
    5. British Nutrition Foundation (2024) Vitamins and Minerals. Vitamins and minerals - British Nutrition Foundation
    6. The Vegan Society (2024) What every vegan should know about vitamin B12. Vegan Nutrition | Vegan B12 | Everything you need to know (vegansociety.com)
    7. Hasudungan, A. (2015) Vitamin B12 Digestion and Absorption. Vitamin B12 Digestion and Absorption (youtube.com)
    8. NHS (2023) Vitamin B12 or folate deficiency anaemia – Overview. Vitamin B12 or folate deficiency anaemia - NHS (www.nhs.uk)
    9. NICE (2023) Anaemia - B12 and folate deficiency: What are the signs and symptoms of vitamin B12 or folate deficiency anaemia? Signs and symptoms | Diagnosis | Anaemia - B12 and folate deficiency | CKS | NICE
    10. University Hospitals Plymouth (2022) Patient Information Leaflet - Vitamin B12 Diet Sheet. cfm (plymouthhospitals.nhs.uk)
    11. Patient (2021) Vitamin B12 Deficiency and Pernicious Anaemia. (Vitamin B12 Deficiency and Pernicious Anaemia | Patient
    12. Hunt, A., Harrington, D., and Robinson, S. (2014) Vitamin B12 deficiency 763683 (bmj.com)
    13. NHS Greater Glasgow and Clyde (2021) Clinical guidelines - Vitamin B12: Treatment of Deficiency in Adults. vit-b12-fp-19.pdf (scot.nhs.uk)
    14. NICE (2023) Anaemia - B12 and folate deficiency: Scenario: Management of anaemia - vitamin B12 and folate deficiency. Scenario: Management | Management | Anaemia - B12 and folate deficiency | CKS | NICE
    15. NICE (2023) Anaemia - B12 and folate deficiency: What causes it? Causes | Background information | Anaemia - B12 and folate deficiency | CKS | NICE
    16. NICE (2023) How common is it? Prevalence | Background information | Anaemia - B12 and folate deficiency | CKS | NICE
    17. Cotton, M. and McCaddon, A. (2023) Examining the Diagnosis and Treatment Experiences of People Living With Autoimmune Gastritis and Pernicious Anaemia. Examining the Diagnosis and Treatment Experiences of People Living With Autoimmune Gastritis and Pernicious Anemia - Martine Cotton, Andrew McCaddon, 2023 (sagepub.com)
    18. Pernicious Anaemia Society (2023) Medical Professionals FAQs. Medical Professional's FAQ's | Pernicious Anaemia Society (pernicious-anaemia-society.org)