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B12 Deficiency: Symptoms, Causes, Testing and Treatment

Learn the signs of vitamin B12 deficiency, who is at risk, how it is diagnosed, the benefits of B12 and how it is treated.

By Editorial Team · Updated · 2 min read

Protein-rich foods including meat, salmon, eggs, nuts and grains laid out on a table
Photo: f0976531950131 · Public domain

This article is awaiting review by a qualified medical professional.

Quick answer

Vitamin B12 deficiency can cause tiredness, pale skin, a sore tongue, tingling in the hands and feet, memory problems and anemia. Common causes are a vegan diet without supplements, pernicious anemia, older age, and medicines such as metformin. It is diagnosed with a blood test and treated with B12 injections or high-dose tablets.

Vitamin B12 (cobalamin) is a nutrient your body cannot make. It is found mainly in animal foods and is needed for healthy nerves, red blood cells and DNA. A shortage can develop slowly over years.

Benefits of vitamin B12

  • Healthy red blood cells: prevents a type of anemia in which red blood cells are too large and work poorly
  • Nerve health: protects the nerves and the covering around them
  • DNA production: needed by every cell in your body
  • Brain function: supports memory and thinking
  • Pregnancy: important for a baby's brain and nervous system development

Extra B12 does not give extra energy, improve mood or help weight loss in people who are not deficient.

Symptoms of B12 deficiency

  • Extreme tiredness and weakness
  • Pale or slightly yellow skin
  • Shortness of breath and dizziness
  • A sore, smooth, red tongue and mouth ulcers
  • Pins and needles, numbness or burning in the hands and feet
  • Difficulty walking or balance problems
  • Memory problems, confusion or low mood
  • Vision changes

Causes and risk factors

  • Vegan or strict vegetarian diet without fortified foods or supplements
  • Pernicious anemia: an autoimmune condition that stops B12 being absorbed from food
  • Older age: lower stomach acid makes absorption harder
  • Metformin for diabetes, and long-term use of acid-reducing medicines
  • Stomach or bowel surgery, including weight-loss surgery
  • Coeliac disease and Crohn's disease
  • Heavy alcohol use
  • Regular nitrous oxide use

How B12 deficiency is diagnosed

A doctor will use blood tests, which may include:

  • Serum B12 level: levels below about 200 pg/mL (148 pmol/L) suggest deficiency, and borderline results are checked further
  • Full blood count to look for anemia
  • Methylmalonic acid or homocysteine, which rise when B12 is low
  • Intrinsic factor antibodies to check for pernicious anemia

Treatment

  • B12 injections are often used at first, especially when there are nerve symptoms or absorption problems
  • High-dose B12 tablets taken daily can also work, even when absorption is poor
  • Diet changes: meat, fish, shellfish, eggs, dairy, and fortified cereals and plant milks
  • Lifelong treatment may be needed for pernicious anemia or after some surgery

Do not self-treat for months without a diagnosis, because other conditions can cause the same symptoms.

When to see a doctor

See a doctor if you have symptoms of B12 deficiency, or if you follow a vegan diet, take metformin, or have a digestive condition. Seek prompt care for numbness, balance problems or confusion, as untreated deficiency can cause permanent nerve damage.

Frequently asked questions

What are the first signs of B12 deficiency?

Early signs are often tiredness, weakness, a sore or red tongue, and pins and needles in the hands or feet. Because these are common to many conditions, a blood test is needed to confirm it.

How much vitamin B12 do adults need?

Adults need about 2.4 micrograms a day, rising to 2.6 in pregnancy and 2.8 while breastfeeding. Most people who eat meat, fish, eggs or dairy get enough, while vegans need fortified foods or a supplement.

Can B12 deficiency be reversed?

Yes, most symptoms improve with treatment. However, nerve damage from a long-standing deficiency may be permanent, which is why early treatment matters.

Does vitamin B12 give you energy?

B12 helps release energy from food and prevents deficiency-related fatigue, but taking extra B12 does not boost energy in people whose levels are already normal.

Sources

  1. NIH Office of Dietary Supplements: Vitamin B12 fact sheet
  2. NHS: Vitamin B12 or folate deficiency anaemia

This article is for educational purposes only and does not replace advice from a doctor or other qualified health professional. See our medical disclaimer.

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