Vitamin B12 deficiency: treatment with injections or tablets

The NHS says vitamin B12 helps keep the nervous system healthy, and that a lack of it can cause the body to produce abnormally large red blood cells that cannot function properly, called vitamin B12 deficiency anaemia. NICE Clinical Knowledge Summaries (CKS) add that deficiency can also exist without anaemia. The key question for treatment is why the level is low, because that decides whether tablets will work and for how long treatment lasts.

The NHS lists extreme tiredness, lack of energy, pins and needles, a sore and red tongue, mouth ulcers, muscle weakness, problems with vision, psychological problems ranging from mild depression or anxiety to confusion and dementia, and problems with memory, understanding and judgement. It says some of these can occur with a deficiency even without anaemia. It advises seeing a GP if you think you may have a deficiency, since these conditions can often be diagnosed from symptoms and a blood test.

The NHS says causes include pernicious anaemia, where the immune system attacks healthy cells in the stomach and prevents absorption of B12 from food (the most common cause in the UK); a lack of B12 in the diet, which is uncommon but can happen on a vegan diet without supplements or fortified foods; and medicines, including anticonvulsants and proton pump inhibitors. CKS adds metformin, colchicine, nitrous oxide and H2-receptor antagonists among drugs, gastric surgery, malabsorption, ileal resection and Crohn's disease as other causes.

The NHS says deficiency is more common in older people, affecting around 1 in 10 people aged 75 or over and 1 in 20 people aged 65 to 74.

CKS says diagnosis rests on history, examination and investigations including a full blood count, blood film and measurement of folate and either total B12 or active B12. An anti-intrinsic factor antibody test should be considered if autoimmune gastritis is suspected or there are strong clinical features of B12 deficiency. If folate is low and malabsorption is suspected, tests for coeliac disease are suggested.

The NHS notes that before folic acid treatment starts, a GP checks B12 levels, because folic acid can improve symptoms so much that it masks an underlying B12 deficiency, which could then affect the nervous system if undetected.

The NHS says B12 deficiency anaemia is usually treated with hydroxocobalamin injections, given by a GP or nurse every other day at first, and that hydroxocobalamin is preferred to cyanocobalamin in the UK because it stays in the body longer. CKS gives the initial injection schedule as three times a week for 2 weeks when the injection route is needed. The long-term plan then depends on the cause.

Numbness or tingling in the hands and feet, unsteadiness, or problems with thinking, memory and behaviour mean the nervous system may be affected. The NHS says people with neurological symptoms are referred to a haematologist, who advises on how long injections should continue. CKS recommends seeking urgent specialist advice and, if advice is not immediately available, considering more frequent hydroxocobalamin injections until there is no further improvement. The NHS warns that some nervous system problems can be permanent, which is why prompt treatment matters.

The NHS says you may need blood tests to check treatment is working: often around 7 to 10 days after starting, to assess haemoglobin and reticulocytes, and another after approximately 8 weeks to confirm success. Most people will not need further monitoring unless symptoms return or treatment is ineffective.

Good dietary sources of B12 according to the NHS are meat, salmon and cod, milk and other dairy products and eggs, and fortified foods such as some yeast extracts, breakfast cereals and soy products for vegetarians and vegans. Diet advice does not replace injections when absorption is the problem.

Folate and B12 deficiency often travel together in the same conversation, but treatment differs. The NHS says folate deficiency anaemia is usually treated with daily folic acid tablets for about 4 months, longer if the cause continues, along with dietary advice. Folic acid on its own should not be used to treat B12 deficiency.

Testing and injections are normally arranged through a GP practice. If neurological symptoms are present, haematology referral is part of the NHS pathway. Private testing of B12 or private injection services exist, but a low result still needs the cause worked out, and any injection schedule should follow the clinical guidance above. Be cautious about regimens that are more frequent than your clinician has recommended without a clear reason.