Vitamin B12 helps your body make healthy red blood cells and keep nerves working. It also supports the production of DNA, the instructions inside your cells. Too little B12 can affect your blood, balance, sensation and thinking. Finding the cause matters because food changes alone do not correct every deficiency.
What does B12 deficiency mean?
Deficiency means the body does not have enough usable vitamin B12. This can happen when intake is too low or when the digestive system cannot absorb it properly. The body stores B12, so symptoms may take years to appear after intake falls. Feeling well today does not prove that a diet will supply enough over time.
B12 deficiency can cause megaloblastic anemia, in which the bone marrow produces unusually large, poorly functioning red blood cells. Anemia reduces the blood’s ability to carry oxygen. However, B12-related nerve problems can occur without anemia or unusually large cells on a blood count. NIH: Vitamin B12
Symptoms to watch for
Possible symptoms include:
- Persistent tiredness, weakness, dizziness or unusual paleness.
- Shortness of breath with activity or a racing or pounding heartbeat.
- A sore, smooth or red tongue, sometimes with mouth ulcers.
- Pins and needles, burning discomfort or numbness in the hands or feet.
- Muscle weakness, difficulty walking, poor balance or coordination.
- Problems with concentration or memory, confusion or changes in mood.
Symptoms can develop gradually and have many other causes. A symptom list cannot diagnose B12 deficiency. NHS: Symptoms
Arrange prompt medical assessment for new or worsening numbness, weakness, balance problems or changes in thinking. Nerve damage may become permanent if treatment is delayed. Do not wait for diet changes or a shop-bought supplement to solve neurological symptoms.
Sudden one-sided weakness, facial drooping or trouble speaking is an emergency. Call local emergency services rather than assuming it is a vitamin problem. CDC: Stroke warning signs
How is vegetarianism related?
People who eat little or no animal food have a higher risk of low B12 intake because ordinary plant foods do not provide a reliable natural supply. This does not mean every vegetarian is deficient. Risk depends on the actual foods eaten, fortified products, supplements and the ability to absorb B12.
Vegetarians who eat dairy products or eggs may obtain B12 from them, but small or occasional amounts may not meet their needs. A vegan diet needs a dependable source from B12-fortified foods and/or an appropriate supplement. A clinician or registered dietitian can help make a plan, particularly during pregnancy, breastfeeding and childhood. MedlinePlus: Food sources and requirements
Reliable sources of B12
- Dairy and eggs: milk, yogurt, cheese and eggs contain B12.
- Other animal foods: fish, shellfish, meat and poultry contain B12 for people who eat them.
- Fortified foods: some breakfast cereals, plant-based milks and nutritional yeast have B12 added. Check the label for vitamin B12 and the amount per serving. Not every product is fortified.
- Supplements: B12 tablets can provide a reliable source when food intake is insufficient. Products and doses differ, so prevention and treatment should not be treated as the same plan.
Vegetables, fruit, pulses and nuts have many nutritional benefits, but they should not be relied on to supply B12 unless specifically fortified. Fortified plant milk can help; unfortified plant milk is not an equivalent B12 source. NHLBI: B12 deficiency and food sources
Diet is only one possible cause
A person who eats animal foods can still develop deficiency. Causes include autoimmune damage to the stomach, often discussed as pernicious anemia, stomach or bowel surgery, and conditions such as coeliac disease or Crohn’s disease. These can interfere with absorption. Long-term use of metformin or some acid-reducing medicines can also increase risk. Do not stop a prescribed medicine yourself; ask whether your symptoms or risk factors warrant testing. NHS: Causes
What might a doctor test?
The assessment usually combines symptoms, diet, medicines and medical history with blood tests. These may include a complete blood count, total or active B12, and folate. If results are borderline or do not fit the symptoms, a clinician may request methylmalonic acid (MMA) or other tests. Further investigation may look for an absorption problem or autoimmune cause.
Tell the clinician about B12 tablets, multivitamins and injections you already use, as they can affect results. Samples are ideally taken before replacement starts, but treatment should not be delayed when a clinician suspects serious B12-related neurological disease. Results need interpretation with symptoms and the laboratory’s reference range, rather than a universal number taken from the internet. NICE: Diagnosis and management
Treatment depends on the cause
Some people need oral B12; others need injections, especially when absorption or neurological problems are involved. The dose, route and duration depend on the cause, severity and response. Some causes require lifelong replacement. Do not assume that a low-dose multivitamin is enough to treat a diagnosed deficiency.
Follow-up checks how symptoms and blood findings respond. Nerve symptoms may improve slowly and do not always fully reverse. Seek reassessment if symptoms worsen, new symptoms appear or treatment is not helping. NHLBI: Treatment and recovery
B12 and folate are different
Folate is vitamin B9. Both vitamins help make blood cells, and either deficiency can cause anemia, but folic acid does not replace B12. Folic acid alone can improve the anemia while an unrecognized B12 deficiency continues to harm nerves. That is why clinicians consider B12 status before treating suspected folate-deficiency anemia. Do not stop prescribed pregnancy folic acid on your own; discuss B12 concerns with your maternity team. NHS: B12 and folate treatment
A practical starting point is to check your regular B12 sources, note persistent symptoms and discuss risk factors with a clinician. Seek prompt help for neurological changes rather than waiting to see whether a dietary change works.
This article provides general health information and does not replace an individual assessment or treatment plan.
Sources and further reading
- NIH Office of Dietary Supplements: Vitamin B12
- MedlinePlus: Vitamin B12
- NHS: Symptoms of B12 or folate deficiency
- NHS: Causes of B12 or folate deficiency
- NHS: Treatment
- NICE NG239: Vitamin B12 deficiency in over 16s
- NHLBI: Vitamin B12-deficiency anemia
- CDC: Stroke warning signs
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