The recommended amount of B12 is 1.5 micrograms daily for UK adults aged 19 to 64 years, according to Department of Health and Social Care guidance. This water-soluble vitamin, also known as cobalamin, is essential for red blood cell formation, nervous system function, and DNA synthesis. Whilst the required amount seems tiny, vitamin B12 plays a vital role in preventing anaemia and neurological complications. Requirements vary across life stages, with breastfeeding women needing 2.0 micrograms daily and children requiring progressively higher amounts as they grow. Understanding your individual B12 needs—and how to meet them through diet, fortified foods, or supplementation—is crucial for maintaining optimal health.

What Is the Recommended Daily Amount of Vitamin B12?

The Reference Nutrient Intake (RNI) for vitamin B12 varies according to age and life stage. In the UK, the Department of Health and Social Care advises that adults aged 19 to 64 years require 1.5 micrograms (µg) of vitamin B12 per day. This recommendation is designed to maintain adequate stores and prevent deficiency in the general population.

For infants and children, requirements increase gradually with age. Babies aged 7 to 9 months need around 0.4 µg daily, whilst those aged 10 to 12 months require 0.5 µg. Children aged 1 to 3 years require 0.5 µg, increasing to 0.8 µg for those aged 4 to 6 years, and 1.0 µg for children aged 7 to 10 years. Adolescents aged 11 to 14 years need 1.2 µg daily, rising to the adult recommendation of 1.5 µg from age 15 onwards. The RNI for adults over 65 years remains at 1.5 µg per day.

For pregnant women, the UK RNI remains at 1.5 µg daily. Breastfeeding women have slightly higher requirements with an RNI of 2.0 µg per day to ensure adequate vitamin B12 passes into breast milk for the infant's neurological development.

It is worth noting that vitamin B12 is measured in micrograms (sometimes labelled as 'mcg' on supplements), which are extremely small units—one microgram equals one millionth of a gram. Despite these tiny amounts, vitamin B12 plays a disproportionately large role in maintaining health. The body stores vitamin B12 primarily in the liver, with reserves typically lasting several years in healthy individuals with adequate intake. However, because the body cannot produce vitamin B12 independently, regular dietary intake or supplementation is essential to maintain these stores and prevent deficiency-related complications.

Why Vitamin B12 Is Essential for Your Health

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that performs several critical functions within the human body. Its primary roles include supporting red blood cell formation, maintaining nervous system integrity, and facilitating DNA synthesis—all processes fundamental to health and wellbeing.

Red blood cell production is perhaps the most recognised function of vitamin B12. The vitamin works alongside folate to enable the maturation of red blood cells in the bone marrow. Without adequate B12, red blood cells become abnormally large and dysfunctional, a condition known as megaloblastic anaemia. This impairs the blood's oxygen-carrying capacity, leading to fatigue, weakness, and breathlessness—symptoms that can significantly impact quality of life.

The neurological functions of vitamin B12 are equally vital. The vitamin is essential for maintaining the myelin sheath, a protective coating surrounding nerve fibres that enables efficient transmission of electrical signals throughout the nervous system. Vitamin B12 deficiency can cause demyelination, resulting in neurological symptoms such as numbness, tingling (particularly in the hands and feet), difficulty walking, memory problems, and mood disturbances. If left untreated, these neurological changes may become irreversible.

Vitamin B12 also plays a crucial role in DNA synthesis and cellular metabolism. It acts as a cofactor for two important enzymes: methionine synthase, which is involved in DNA production and the metabolism of homocysteine (an amino acid that may be linked to cardiovascular risk when elevated), and methylmalonyl-CoA mutase, which is essential for energy production from fats and proteins. Through these mechanisms, vitamin B12 supports cellular growth, repair, and energy metabolism throughout the body. Adequate B12 status is therefore important not only for preventing deficiency diseases but also for maintaining optimal physiological function across multiple organ systems.

Who Is at Higher Risk of Vitamin B12 Deficiency?

Certain groups are at increased risk of vitamin B12 deficiency, primarily due to impaired absorption or inadequate dietary intake. Identifying these at-risk populations is essential for preventing deficiency and its associated complications.

Older adults are at significantly increased risk of vitamin B12 deficiency. Age-related changes in the gastrointestinal tract, particularly reduced stomach acid production (achlorhydria or hypochlorhydria), impair the release of vitamin B12 from food proteins. Additionally, atrophic gastritis—inflammation and thinning of the stomach lining—affects many older adults and further compromises B12 absorption. Older adults with risk factors may benefit from discussing their B12 status with a GP or dietitian, who can advise on appropriate fortified foods or supplements.

Individuals following plant-based diets—including vegans and, to a lesser extent, vegetarians—face particular challenges in meeting B12 requirements. Vitamin B12 is naturally found almost exclusively in animal-derived foods, meaning those who avoid meat, fish, eggs, and dairy products are at high risk of deficiency unless they consume fortified foods or take supplements. The British Dietetic Association recommends that vegans take a daily B12 supplement of at least 10 µg or a weekly supplement of 2,000 µg. Unfortified plant foods such as seaweed, spirulina or fermented foods are unreliable sources of active B12.

People with malabsorption conditions require special consideration. Conditions such as pernicious anaemia (an autoimmune condition affecting intrinsic factor production, which should be confirmed with intrinsic factor antibody testing), Crohn's disease, coeliac disease, and those who have undergone gastric surgery (including bariatric procedures) may have severely impaired B12 absorption. These individuals often require intramuscular B12 injections rather than oral supplementation. In the UK, hydroxocobalamin 1 mg is typically administered three times a week for two weeks (if no neurological symptoms are present), followed by maintenance doses of 1 mg every 2-3 months. If neurological symptoms are present, treatment may involve 1 mg on alternate days until no further improvement, then maintenance doses of 1 mg every 2 months.

Additionally, long-term use of certain medications can interfere with B12 absorption. The Medicines and Healthcare products Regulatory Agency (MHRA) advises that metformin can reduce vitamin B12 levels and recommends checking B12 status in patients with symptoms of deficiency and considering periodic monitoring in those with risk factors. Proton pump inhibitors (PPIs) and H2-receptor antagonists may also affect B12 absorption with long-term use. Patients should not stop prescribed medications without consulting their healthcare provider.

Signs You May Not Be Getting Enough Vitamin B12

Vitamin B12 deficiency develops gradually, often over months or years, as the body depletes its hepatic stores. Early recognition of deficiency signs is important, as prompt treatment can prevent irreversible neurological damage.

Haematological symptoms typically appear first and include fatigue, weakness, and breathlessness—manifestations of megaloblastic anaemia. Individuals may appear pale or develop a slight yellowing of the skin (jaundice) due to increased breakdown of abnormal red blood cells. Some people notice a sore, red tongue (glossitis) or mouth ulcers. These symptoms reflect impaired red blood cell production and reduced oxygen delivery to tissues.

Neurological and psychiatric manifestations can be more insidious and may occur even before anaemia develops. Common neurological symptoms include:

• Paraesthesia (pins and needles) in the hands and feet

• Numbness or altered sensation

• Difficulty walking or balance problems (sensory ataxia)

• Muscle weakness and reduced coordination

• Cognitive changes, including memory problems, confusion, or difficulty concentrating

• Mood disturbances, such as depression or irritability

In severe cases, vitamin B12 deficiency can cause subacute combined degeneration of the spinal cord, a serious condition affecting both sensory and motor pathways. This presents with progressive weakness, spasticity, and sensory loss, and requires urgent medical attention.

When to contact your GP: You should arrange an appointment if you experience persistent fatigue alongside any neurological symptoms, particularly if you belong to an at-risk group. For acute neurological symptoms, arrange a same-day GP appointment or contact NHS 111. If you develop sudden or severe neurological symptoms—such as significant weakness, loss of balance, or marked confusion—call 999 for emergency assessment.

Diagnosis typically involves blood tests measuring serum B12 levels, full blood count, and sometimes additional markers such as methylmalonic acid or homocysteine in equivocal cases. Intrinsic factor antibodies and red cell folate may also be tested where appropriate. Importantly, folic acid should not be given until vitamin B12 deficiency has been excluded or treated, as this can worsen neurological damage. Treatment should not be delayed whilst awaiting test results if clinical suspicion of deficiency is high, particularly when neurological symptoms are present.

How to Meet Your Daily B12 Requirements

Meeting your daily vitamin B12 requirements is achievable through a combination of dietary sources, fortified foods, and supplements when necessary. The approach depends on your dietary preferences, age, and any underlying health conditions.

Dietary sources provide the most natural route to adequate B12 intake for those consuming animal products. Excellent sources include:

• Meat and poultry: Beef, lamb, pork, and chicken (liver and kidney are particularly rich sources but should be avoided during pregnancy due to their vitamin A content)

• Fish and seafood: Salmon, trout, tuna, sardines, and shellfish such as mussels and crab

• Dairy products: Milk, cheese, and yoghurt

• Eggs: Particularly the yolk

A varied diet including these foods typically provides well above the recommended 1.5 µg daily. For example, a 100g portion of salmon contains approximately 3–4 µg of vitamin B12, whilst a glass of milk provides around 0.6 µg.

Fortified foods are essential for those following plant-based diets. Many breakfast cereals, plant-based milk alternatives (soya, almond, oat), yeast extracts, and nutritional yeast are fortified with vitamin B12. Always check product labels, as fortification levels vary considerably between brands. Consuming fortified foods several times daily can help vegans and vegetarians meet their requirements, though supplementation is generally more reliable.

Supplementation is recommended for at-risk groups. Oral supplements are available in various forms, including cyanocobalamin and methylcobalamin, with doses typically ranging from 10 µg to 2,000 µg. The British Dietetic Association recommends that vegans take either at least 10 µg daily or 2,000 µg weekly, with cyanocobalamin being a commonly recommended form. For most people, oral supplementation is effective and well-tolerated.

Individuals with malabsorption conditions or pernicious anaemia require intramuscular injections of hydroxocobalamin. In the UK, the standard regimen is 1 mg administered three times a week for two weeks (if no neurological symptoms are present), followed by maintenance doses of 1 mg every 2-3 months. If neurological symptoms are present, treatment may involve 1 mg on alternate days until no further improvement, then maintenance doses of 1 mg every 2 months.

Vitamin B12 has a very low toxicity profile, and there is no established upper limit for intake in the UK, as excess amounts are readily excreted in urine. However, it is always advisable to follow dosing recommendations and consult your GP or a registered dietitian if you are unsure about supplementation. If you experience any suspected adverse effects from supplements or injections, report them through the MHRA Yellow Card scheme. Regular monitoring through blood tests may be appropriate for those at high risk of deficiency or those receiving treatment for confirmed deficiency.

Frequently Asked Questions