Vitamin B12, also known as cobalamin, is a water-soluble vitamin essential for red blood cell production, nervous system health, and DNA synthesis. This vital nutrient supports oxygen transport throughout the body, maintains the protective myelin sheath around nerve fibres, and works alongside folate in cell division. Whilst the body stores B12 in the liver for several years, regular dietary intake remains important. Deficiency can lead to megaloblastic anaemia and potentially irreversible neurological damage. Understanding what B12 does helps identify those at risk and ensures appropriate dietary intake or supplementation when needed.

What Does Vitamin B12 Do in Your Body?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that plays essential roles in maintaining human health. B12 is stored primarily in the liver, with substantial reserves that can last for 2-4 years, though regular dietary intake remains important for optimal health.

This vitamin is crucial for the production of red blood cells in the bone marrow. Without adequate B12, red blood cells develop abnormally large and cannot function properly, leading to a condition called megaloblastic anaemia. These malformed cells are less efficient at carrying oxygen throughout the body, which can result in fatigue and weakness.

B12 is also vital for maintaining the health of the nervous system. It contributes to the formation and maintenance of myelin, the protective sheath that surrounds nerve fibres and enables efficient transmission of nerve signals. Damage to this myelin sheath due to B12 deficiency can lead to neurological symptoms that may become irreversible if left untreated.

Additionally, vitamin B12 works alongside folate (vitamin B9) in DNA synthesis and cell division. This partnership is particularly important during periods of rapid cell growth, such as during pregnancy and infancy. B12 also plays a role in metabolising homocysteine, an amino acid that, when elevated, has been associated with increased cardiovascular risk. However, while B12 can lower homocysteine levels when deficient, supplementation has not been shown to reduce cardiovascular events in clinical trials.

Key Functions and Health Benefits of B12

The physiological functions of vitamin B12 extend across multiple body systems, making it indispensable for overall health and wellbeing.

Haematological function: B12 is essential for normal red blood cell formation. It acts as a cofactor for methionine synthase, enabling folate-dependent DNA synthesis necessary for proper cell division. Without adequate B12, DNA synthesis is impaired, leading to megaloblastic changes in developing red blood cells and ultimately anaemia.

Neurological health: The vitamin supports cognitive function and helps maintain the structural integrity of the central and peripheral nervous systems. B12 deficiency has been associated with memory problems, difficulty concentrating, and in severe cases, peripheral neuropathy characterised by tingling, numbness, or burning sensations in the hands and feet. Early detection and treatment are crucial, as some neurological damage may be permanent.

Energy metabolism: Whilst B12 is often marketed for 'energy boosting', its role is more nuanced. The vitamin participates in the metabolism of fats and carbohydrates, helping convert food into usable energy at the cellular level. However, there is no official link between B12 supplementation and increased energy in individuals with normal B12 status.

Mood and mental health: Some research suggests a relationship between B12 levels and mood regulation, though the evidence remains inconclusive. B12 is involved in the synthesis of neurotransmitters such as serotonin and dopamine, which influence mood. However, supplementation has not been definitively proven to improve depression or anxiety in those without deficiency.

Signs You May Need More Vitamin B12

Vitamin B12 deficiency can develop gradually, and symptoms may be subtle initially, making early recognition challenging. The clinical presentation varies depending on the severity and duration of deficiency.

Haematological symptoms often appear first and include:

• Persistent tiredness and weakness that doesn't improve with rest

• Breathlessness, even with minimal exertion

• Pale or jaundiced (yellowish) skin

• Heart palpitations or rapid heartbeat

Neurological and cognitive symptoms may develop alongside or independently of anaemia:

• Pins and needles sensation (paraesthesia), typically in hands and feet

• Difficulty walking or problems with balance

• Memory problems or difficulty concentrating

• Mood changes, including depression or irritability

• Glossitis (sore, red tongue) or mouth ulcers

In severe or prolonged deficiency, more serious neurological complications can occur, including peripheral neuropathy, subacute combined degeneration of the spinal cord, and cognitive impairment. These conditions underscore the importance of early detection and treatment.

It is important to note that these symptoms are non-specific and can be caused by numerous other conditions. If you experience persistent symptoms, particularly neurological signs, you should contact your GP promptly. Blood tests measuring serum B12 levels, along with full blood count and other markers, can confirm deficiency. If results are borderline or discordant with symptoms, additional tests such as holotranscobalamin or methylmalonic acid may be helpful. Anti-intrinsic factor antibodies may be tested when pernicious anaemia is suspected.

Importantly, if significant neurological symptoms suggest B12 deficiency, treatment should be started promptly and not delayed while awaiting test results. Additionally, folic acid should not be given alone when B12 deficiency is suspected, as it may mask anaemia while allowing neurological damage to progress.

How to Get Enough B12: Food Sources and Supplements

Vitamin B12 is naturally found almost exclusively in animal-derived foods, which presents particular challenges for those following plant-based diets.

Dietary sources rich in B12 include:

• Meat and poultry: Beef, lamb, pork, and chicken, particularly organ meats like liver and kidney

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

• Dairy products: Milk, cheese, and yoghurt provide moderate amounts

• Eggs: Particularly the yolk

• Fortified foods: Many breakfast cereals, plant-based milk alternatives, and fortified nutritional yeast contain added B12

The recommended daily intake for adults in the UK is 1.5 micrograms, according to NHS guidance. Most people consuming a varied diet including animal products can meet this requirement through food alone.

Supplementation may be necessary for certain groups. B12 supplements are available in several forms:

• Oral tablets: Cyanocobalamin is the most common and stable form, whilst methylcobalamin is also available. Oral supplements (typically 50-150 micrograms daily between meals) are appropriate for dietary deficiency.

• Sublingual preparations: Designed to dissolve under the tongue, though these have no proven advantage over standard oral tablets

• Intramuscular injections: Hydroxocobalamin injections are used when oral absorption is impaired

For those with pernicious anaemia or malabsorption conditions, oral supplementation is often ineffective, and lifelong B12 injections are required. The standard treatment regimen for B12 deficiency without neurological involvement is 1 mg hydroxocobalamin intramuscularly three times a week for 2 weeks. For those with neurological symptoms, 1 mg is given on alternate days until no further improvement, followed by maintenance therapy. Maintenance doses are typically 1 mg every 2-3 months.

If you are considering B12 supplements, discuss this with your GP or a registered dietitian, particularly if you have existing health conditions or take medications that may interact with supplementation.

Who Is at Risk of B12 Deficiency in the UK?

Certain population groups face increased risk of developing vitamin B12 deficiency due to dietary, physiological, or medical factors.

Dietary factors:

• Vegans and strict vegetarians: As B12 is found almost exclusively in animal products, those avoiding all animal-derived foods are at high risk unless they consume fortified foods or supplements regularly

• Older adults: Reduced stomach acid production with age can impair B12 absorption from food, with risk increasing progressively with advancing age

Medical conditions affecting absorption:

• Pernicious anaemia: An autoimmune condition where the body cannot produce intrinsic factor, a protein essential for B12 absorption in the small intestine

• Gastrointestinal disorders: Crohn's disease, coeliac disease, and other conditions affecting the terminal ileum can impair B12 uptake

• Post-surgical patients: Those who have undergone gastric bypass or removal of parts of the stomach or small intestine

Medication-related risk:

• Metformin: Commonly prescribed for type 2 diabetes, long-term use can reduce B12 absorption. The MHRA advises checking B12 levels if symptoms occur and considering periodic monitoring in those at risk.

• Proton pump inhibitors (PPIs): Used for acid reflux, these medications reduce stomach acid needed to release B12 from food

• H2-receptor antagonists: Another class of acid-suppressing medications

Other at-risk groups:

• Pregnant and breastfeeding women, particularly those following plant-based diets

• Individuals with chronic alcohol misuse

• People exposed to nitrous oxide (recreational or occupational), which can cause rapid B12 inactivation and neurological deterioration

While routine population screening is not recommended, testing for B12 deficiency should be considered in those with risk factors or suggestive symptoms. If you fall into any of these categories, speak with your GP about whether B12 testing or supplementation is appropriate for you.

Frequently Asked Questions