Vitamin B12 (cobalamin) is essential for red blood cell formation, neurological function, and DNA synthesis. In the UK, adults aged 15 and over require 1.5 micrograms (mcg) per day, according to the Department of Health's Reference Nutrient Intake. This modest requirement reflects the body's efficient recycling mechanisms and substantial liver storage capacity. Whilst most people obtain adequate B12 through a balanced diet containing animal products, certain groups—including vegans, older adults, and those with malabsorption conditions—may need additional attention to their B12 status. Understanding daily requirements helps ensure optimal health across all life stages.

Recommended Daily B12 Intake in the UK

Vitamin B12 (cobalamin) is an essential water-soluble vitamin that plays a critical role in red blood cell formation, neurological function, and DNA synthesis. In the United Kingdom, the Reference Nutrient Intake (RNI) for vitamin B12 is set at 1.5 micrograms (mcg) per day for adults aged 15 years and over, as established by the Department of Health's Committee on Medical Aspects of Food Policy (COMA).

The RNI represents the amount of a nutrient sufficient to ensure that the needs of nearly all individuals in a group are met. For vitamin B12, this relatively modest daily requirement reflects the body's efficient recycling mechanisms and the vitamin's storage capacity in the liver, which can maintain reserves for several years (typically 2-5 mg). Unlike some other vitamins, B12 is not required in large quantities, but consistent intake is essential because the body cannot synthesise it independently.

NHS guidance emphasises that most people should be able to obtain adequate B12 through a balanced diet containing animal products. However, certain population groups—including older adults, vegans, and individuals with malabsorption conditions—may require additional attention to their B12 status. The UK's approach differs slightly from recommendations by the European Food Safety Authority (EFSA), which sets an Adequate Intake of 4 mcg per day for adults, reflecting a more cautious margin of safety. Understanding these baseline requirements helps individuals and healthcare professionals assess whether dietary intake or supplementation may be necessary.

How Much Vitamin B12 Do Different Age Groups Need?

Vitamin B12 requirements vary across the lifespan, reflecting changing physiological needs during growth, development, and ageing. The UK's Reference Nutrient Intakes provide age-specific guidance to ensure optimal health at every stage.

Infants and young children have lower absolute requirements but higher needs relative to body weight. For infants aged 0–6 months, the RNI is 0.3 mcg per day, rising to 0.4 mcg per day for those aged 7–12 months. These needs are typically met through breast milk or infant formula. For children aged 1–3 years, the recommendation increases to 0.5 mcg per day, then to 0.8 mcg per day for ages 4–6 years, and 1.0 mcg per day for ages 7–10 years.

Adolescents aged 11–14 years require 1.2 mcg per day, reflecting increased demands during puberty and rapid growth. From age 15 onwards through adulthood, the standard RNI of 1.5 mcg per day applies to both men and women.

Pregnant women maintain the same RNI of 1.5 mcg per day as non-pregnant women. Lactating women require more to ensure adequate B12 in breast milk, with an RNI of 2.0 mcg per day.

Older adults maintain the same 1.5 mcg RNI, but absorption efficiency often declines with age due to reduced stomach acid production and intrinsic factor availability. The British Dietetic Association notes that adults over 50 may benefit from fortified foods or supplements to compensate for reduced absorption. Testing for B12 status should be based on symptoms or risk factors rather than routine screening, with healthcare professionals assessing individuals who may be at higher risk of deficiency.

When You Might Need Higher B12 Doses

While the standard RNI of 1.5 mcg per day suffices for most healthy adults, certain medical conditions, dietary patterns, and medications can substantially increase B12 requirements or impair absorption, necessitating higher therapeutic doses under medical supervision.

Pernicious anaemia, an autoimmune condition affecting approximately 0.1-0.2% of the UK population (higher in older adults), destroys gastric parietal cells that produce intrinsic factor—a protein essential for B12 absorption in the terminal ileum. Patients with this condition typically require injectable B12. According to NICE Clinical Knowledge Summaries and the British National Formulary, the standard treatment is intramuscular injections of 1,000 mcg (1 mg) hydroxocobalamin. For patients without neurological involvement, this is given three times weekly for two weeks; for those with neurological symptoms, it's given on alternate days until no further improvement occurs. Maintenance therapy is typically 1 mg every 2–3 months for life. While high-dose oral B12 (1,000 mcg daily) may be effective in some cases, intramuscular hydroxocobalamin remains the standard NHS practice.

Gastrointestinal disorders including Crohn's disease, coeliac disease, and previous gastric or ileal surgery can severely compromise B12 absorption. These patients often require therapeutic doses under medical supervision. Metformin, commonly prescribed for type 2 diabetes, can reduce B12 absorption with long-term use. The MHRA recommends considering periodic B12 monitoring in patients on metformin who have risk factors for deficiency, and testing if symptoms develop.

Proton pump inhibitors (PPIs) and H2-receptor antagonists, used for acid reflux, reduce stomach acid production and may affect B12 release from food proteins. Long-term users should be assessed if symptoms of deficiency develop, with supplementation provided if deficiency is confirmed.

Strict vegans and vegetarians consuming no animal products require reliable B12 sources through fortified foods or supplements, typically 10 mcg daily or 2,000 mcg weekly, as recommended by the British Dietetic Association. Absorption efficiency decreases with higher single doses, which explains these supplementation strategies.

Signs You're Not Getting Enough B12

Vitamin B12 deficiency develops insidiously, often over months to years, as the liver's substantial reserves become gradually depleted. Recognising early warning signs is crucial because neurological damage can become irreversible if deficiency persists untreated.

Haematological manifestations typically appear first. Macrocytic anaemia—characterised by abnormally large red blood cells—develops as B12 deficiency impairs DNA synthesis. Patients may experience progressive fatigue, weakness, pallor, and shortness of breath on exertion. However, folate supplementation can mask these haematological changes whilst neurological damage continues, highlighting the importance of checking B12 status before commencing folate therapy.

Neurological symptoms can occur even before anaemia develops and include paraesthesia (pins and needles) in the hands and feet, numbness, difficulty walking, and balance problems due to subacute combined degeneration of the spinal cord. Cognitive changes may manifest as memory impairment, confusion, depression, or irritability. In severe cases, patients may develop visual disturbances due to optic neuropathy.

Other symptoms include glossitis (sore, red tongue) and mouth ulcers. Some patients may experience unexplained weight loss.

When to seek medical attention: Contact your GP if you experience persistent fatigue alongside neurological symptoms, particularly if you have risk factors such as being vegan, having gastrointestinal disease, or taking medications affecting B12 absorption. The NHS recommends urgent assessment for rapidly progressive neurological symptoms. Diagnosis involves serum B12 measurement (levels below 148 pmol/L indicate deficiency; 148–258 pmol/L may warrant further investigation with methylmalonic acid or homocysteine testing). Anti-intrinsic factor antibodies help diagnose pernicious anaemia. According to the British Society for Haematology, treatment should not be delayed when neurological symptoms are present. Early detection and treatment prevent irreversible complications.

How to Meet Your Daily B12 Requirements

Meeting the UK's recommended 1.5 mcg daily B12 intake is straightforward for most people consuming animal products, as vitamin B12 is found almost exclusively in foods of animal origin. Understanding rich dietary sources and appropriate supplementation strategies ensures adequate intake across different dietary patterns.

Excellent dietary sources include:

• Liver and organ meats: Beef liver provides approximately 70 mcg per 100g—far exceeding daily needs

• Shellfish: Clams, mussels, and crab are exceptionally rich sources

• Fish: Salmon (5 mcg per 100g), trout, tuna, and mackerel provide substantial amounts

• Meat and poultry: Beef, lamb, and chicken contain 1–3 mcg per 100g

• Dairy products: Milk (0.4 mcg per 100ml), cheese, and yoghurt contribute meaningfully

• Eggs: One large egg provides approximately 0.6 mcg

For vegans and vegetarians, reliable B12 sources are essential as plant foods contain no bioavailable B12 (despite some claims about algae or fermented products). Options include:

• Fortified foods: Nutritional yeast, plant-based milk alternatives, breakfast cereals, and meat substitutes fortified with B12 (check labels for content)

• Supplements: Daily supplements of 10 mcg or weekly doses of 2,000 mcg ensure adequate intake, as recommended by the British Dietetic Association

The body absorbs approximately 50% of a 1–2 mcg dose but only about 1% of a 1,000 mcg dose through passive diffusion. This explains why therapeutic doses are substantially higher than dietary requirements.

Practical tips for optimising B12 status include consuming B12-rich foods regularly throughout the week rather than sporadically, considering fortified foods if reducing animal product intake, and discussing supplementation with your GP or registered dietitian if you have absorption concerns. For those requiring supplements, cyanocobalamin and hydroxocobalamin are both effective forms available in the UK, with hydroxocobalamin preferred for injections due to superior tissue retention, as noted in the British National Formulary.

Frequently Asked Questions