Find out how much vitamin B12 you need per day based on your age, sex, and life stage — with extra guidance for vegans and vegetarians.
Vitamin B12 (cobalamin) is essential for:
Red blood cell formation: B12 is needed to make healthy red blood cells. Deficiency leads to megaloblastic anaemia — large, immature red blood cells that can't carry oxygen efficiently.
Nervous system function: B12 maintains the myelin sheath that protects nerve fibres. Deficiency can cause peripheral neuropathy (numbness, tingling), difficulty walking, and cognitive problems.
DNA synthesis: Every cell in your body needs B12 to divide properly. This is particularly important during pregnancy and for growing children.
Homocysteine metabolism: B12 helps convert homocysteine to methionine. Elevated homocysteine (from B12 or folate deficiency) is a risk factor for cardiovascular disease.
Vegans and strict vegetarians: B12 is only found naturally in animal products (meat, fish, eggs, dairy). If you eat no animal products, you must supplement or eat B12-fortified foods.
Adults over 50: Up to 30% of older adults have reduced stomach acid (atrophic gastritis), which impairs B12 absorption from food. Crystalline B12 in supplements and fortified foods is still absorbed normally.
People with GI conditions: Crohn's disease, coeliac disease, and other conditions affecting the small intestine can reduce B12 absorption.
Pernicious anaemia: An autoimmune condition where the body cannot make intrinsic factor (needed to absorb B12). Requires lifelong B12 injections.
Metformin users: Long-term metformin use (for type 2 diabetes) can reduce B12 absorption. Annual B12 monitoring is recommended.
Post-bariatric surgery: Gastric bypass and sleeve gastrectomy reduce B12 absorption. Lifelong supplementation is required.
Proton pump inhibitors (PPIs): Long-term use of omeprazole, pantoprazole, etc. can reduce B12 absorption by lowering stomach acid.
Animal sources (naturally occurring):
Beef liver (75g): 53µg. Clams (75g): 74µg. Salmon (100g): 3.2µg. Beef (100g): 2.5µg. Tuna (100g): 2.2µg. Milk (250ml): 1.2µg. Eggs (2 large): 1.6µg. Yoghurt (200g): 1.0µg. Cheese (30g): 0.4µg. Chicken (100g): 0.3µg.
Fortified foods (for vegans/vegetarians):
Nutritional yeast (1 tbsp, fortified): 2.0–4.0µg. Soy milk (250ml, fortified): 1.0–2.5µg. Plant-based meat (1 serve, fortified): 0.5–2.5µg. Fortified breakfast cereal (1 serve): 0.6–2.0µg. Marmite/Vegemite (1 tsp): 0.5µg.
Important: Nori, tempeh, spirulina, and mushrooms are sometimes claimed as plant B12 sources, but they contain B12 analogues that are not bioavailable — your body cannot use them. Vegans must use supplements or reliably fortified foods.
See your GP about vitamin B12 if you:
Experience persistent fatigue, weakness, or shortness of breath. Have numbness, tingling, or pins and needles in your hands or feet. Notice balance problems or difficulty walking. Have mood changes, memory problems, or confusion. Follow a vegan or vegetarian diet and have not been supplementing. Take metformin, PPIs, or other medications that affect B12. Have had bariatric surgery. Have a family history of pernicious anaemia.
Your GP can check your B12 level with a simple blood test. If deficiency is confirmed, treatment may include high-dose oral supplements or B12 injections depending on the cause and severity.