Vitamin B12 Deficiency: Causes, Testing and Treatment Overview

Overview

Vitamin B12 deficiency means the body does not have enough of the vitamin. It can happen because too little is eaten, but more often because too little is absorbed. The NHS (UK) says it is important for B12 or folate deficiency anemia to be diagnosed and treated as soon as possible, because some problems can be permanent. [1] This page explains the usual causes, tests and treatments so you can have a better conversation with a clinician. It is not a self-test. For the vitamin itself see Vitamin B12, and for everyday tiredness see Why am I so tired?.

Why seeing a clinician matters

The NHS says some symptoms improve with treatment but others can be irreversible if left untreated, and the longer the condition goes untreated, the higher the chance of permanent damage. [2] It lists nervous-system problems among complications that can sometimes be permanent. [1] Low B12 should not be treated on a guess. Ask a GP, doctor or pharmacist before starting a supplement, and do not stop a prescribed medicine yourself.

Symptoms (many have other causes)

The NHS lists extreme tiredness, lack of energy, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, and psychological changes from mild depression or anxiety to confusion and dementia. [1] Nervous-system symptoms can include numbness, problems with balance and coordination, and incontinence. [2] MedlinePlus (US) lists anemia, loss of balance, numbness or tingling in the arms and legs, weakness and dementia due to metabolic causes. [3] These symptoms overlap with many other conditions, and some can occur without anemia. [2] Symptoms alone cannot confirm deficiency.

Causes

Deficiency is more common with age: the NHS says B12 or folate deficiency affects around 1 in 10 people aged 75 or over and 1 in 20 aged 65 to 74 (UK). [1] MedlinePlus lists people over 50, people on vegetarian or vegan diets, people who have had stomach or intestinal surgery including weight-loss surgery, and people with celiac or Crohn disease. [3] See Pernicious Anemia and Intrinsic Factor and Vitamin B12 and Medicines.

Testing and its limits

• First tests. Blood tests check hemoglobin, red blood cell size, B12 and folate. The NHS notes that some people have symptoms with normal levels and others have low levels with no symptoms, so symptoms are considered too. [5]
• Serum B12 has limits. A review in the journal Frontiers in Molecular Biosciences says serum B12 has limited value as a stand-alone marker: low levels do not always mean deficiency, and severe functional deficiency has been documented with normal or even high levels. [6]
• Methylmalonic acid (MMA). A US family-medicine review says serum MMA should be used to confirm deficiency in high-risk people without symptoms who have low-normal B12. [7] See Vitamin B12 Tests.
• Pernicious anemia tests. Extra blood tests are used but are not always conclusive. [5]
• Folic acid can mask B12 deficiency. Before folic acid treatment the NHS says the GP checks B12 levels, because folic acid can improve symptoms enough to hide a B12 deficiency. [8]
• Other factors. MedlinePlus says B vitamin test results are not always clear: inflammation and certain medicines can affect them, and labs use different ranges. [9]
• Home or mail-order B12 tests: Proper evidence not found in the NHS, MedlinePlus and PubMed pages we read, so none is described. See At-Home Vitamin Test Kits.

Who may be screened

The same US review says screening average-risk adults is not recommended, and lists risk factors for which screening may be warranted: stomach or small-intestine surgery, inflammatory bowel disease, metformin for more than four months, PPIs or H2 blockers for more than 12 months, vegans or strict vegetarians, and adults older than 75. [7]

Treatment overview (UK guidance, clinician-led)

This describes what NHS guidance says; your clinician decides what applies to you.

• B12 deficiency anemia is usually treated with injections of hydroxocobalamin, given every other day at first. [8]
• If the cause is diet, the NHS says tablets daily between meals or an injection twice a year may be advised, and people who cannot get enough from diet, such as vegans, may need tablets for life. [8]
• If the cause is not diet-related, such as pernicious anemia, an injection every 2 to 3 months for life is usual, and every 2 months if there are neurological symptoms. [8]
• Oral compared with injection. A Cochrane review of three small trials (153 people, 3 to 4 months) found low-quality evidence of no clinically relevant difference in blood B12 between 1,000 mcg a day by mouth and injection. These were study amounts, not advice. [10] A clinical review says injections work faster and should be considered for severe deficiency or severe nerve symptoms. [7] See Vitamin B12 Injections.
• Follow-up. The NHS describes blood tests around 7 to 10 days and about 8 weeks after starting treatment. [8]

Official intake references

For adults in the UK, the NHS says 2 mg a day or less from supplements is unlikely to cause harm, though there is not enough evidence on the effects of high doses. [11] See RDA, AI, DV and UL for how these terms differ.