What Are the Symptoms of Vitamin B12 Deficiency? Who Gets It?

In brief:

• B12 helps make red blood cells and keeps the nervous system healthy (NHS).
• Adults need about 1.5 micrograms of B12 a day (NHS); the NIH gives 2.4 micrograms.
• B12 is found naturally only in animal foods; people on a vegan diet are at risk of deficiency (NHS, NIH).
• Medicines that reduce stomach acid and metformin can reduce B12 absorption (NIH).
• Symptoms can occur even without anaemia. Early diagnosis matters because some nervous system problems can become permanent if treatment is delayed (NHS).

What does B12 do?

According to the NHS, B12 helps the body:

• make red blood cells and keep the nervous system healthy;
• release energy from food;
• use folate.

According to the NIH, B12 also helps make DNA, the genetic material in cells. In B12 deficiency the body produces abnormally large red blood cells that cannot work properly; this is called B12 deficiency anaemia (NHS).

What are the symptoms of B12 deficiency?

According to the NHS, B12 or folate deficiency can cause:

• Extreme tiredness
• Lack of energy
• Pins and needles
• A sore and red tongue
• Mouth ulcers
• Muscle weakness
• Problems with your vision
• Psychological problems, ranging from mild depression or anxiety to confusion and dementia
• Problems with memory, understanding and judgement

The NIH adds pale skin, palpitations, loss of appetite, weight loss, numbness in the hands and feet, balance problems and infertility.

According to the NHS, some of these problems can occur even before anaemia develops. According to the NIH, the body stores 1,000–2,000 times as much B12 as you take in a day. This is why symptoms can take years to appear.

Tiredness and forgetfulness also have other causes. For example, tiredness is common in iron deficiency too; we explain it in Iron Deficiency Symptoms.

What causes B12 deficiency?

Common causes according to the NHS and the NIH:

• Pernicious anaemia: a condition in which the immune system attacks healthy cells in the stomach and B12 cannot be absorbed from food. According to the NHS, it is the most common cause of B12 deficiency in the UK.
• Older age: according to the NIH, many older people do not have enough stomach acid to separate B12 from food. According to the NHS, B12 or folate deficiency affects about 1 in 10 people aged 75 and over and 1 in 20 people aged 65 to 74.
• Diet: B12 occurs naturally only in animal foods (NIH). According to the NHS, deficiency caused by diet is not common. However, it can occur in people on a vegan diet who do not take B12 supplements or foods with added B12, in people with very restricted diets, or in people who have had a poor diet for a long time.
• Stomach and bowel surgery and conditions: weight-loss surgery or removal of part of the stomach, coeliac disease and Crohn's disease (NIH).
• Medicines: medicines that reduce stomach acid (proton pump inhibitors), epilepsy medicines (NHS) and metformin, used in diabetes (NIH), can reduce B12 absorption.

Pregnancy and breastfeeding: according to the NIH, needs increase during pregnancy and breastfeeding. If a pregnant or breastfeeding mother is vegan or strictly vegetarian, the baby may not get enough B12 either.

How is B12 deficiency diagnosed?

According to the NHS, B12 deficiency is usually diagnosed from your symptoms and the result of a blood test. A full blood count shows whether the number of red blood cells is normal; the same test also looks for anaemias caused by B12 and folate deficiency (NHS). If needed, the doctor also checks the B12 level in the blood (NIH).

We explain which tests to have and when in Tests Every Woman Should Have Once a Year.

What is done for B12 deficiency?

According to the NHS, most B12 deficiency can be easily treated by replacing the missing vitamin with injections or tablets:

• At first, B12 is usually given by injection.
• If the deficiency is related to diet, tablets between meals may be needed afterwards; if not, regular injections may be needed.
• Treatment may last until the B12 level improves, or for life.

Your doctor will decide which approach is right for you. According to the NIH, people with pernicious anaemia absorb B12 poorly from both food and supplements, so doctors usually recommend B12 injections.

How much B12 do you need a day?

The two sources give different values; countries set their recommendations using different methods.

Which foods contain B12? According to the NHS: meat, fish, milk, cheese, eggs and some breakfast cereals with added B12. According to the NIH, clams, oysters and beef liver are among the best sources. Plant foods do not contain B12 unless it has been added (NIH).

Is too much harmful? According to the NHS, there is not enough evidence to show the effects of high-dose B12 supplements; taking 2 mg or less of B12 a day from supplements is unlikely to cause harm.

When should you see a doctor?

• You think you may have B12 or folate deficiency (NHS)
• You notice numbness or tingling in your hands and feet, balance problems or forgetfulness
• You are vegan and do not take B12 supplements or foods with added B12
• You have been taking a medicine that reduces stomach acid or metformin for a long time; do not stop your medicine on your own, ask your doctor
• You are pregnant, breastfeeding or planning a pregnancy

According to the NHS, early diagnosis matters: most symptoms improve with treatment, but some problems can be permanent.

Frequently asked

Can B12 deficiency cause hair loss?

The sources in this article do not list hair loss among the symptoms of B12 deficiency. The NHS lists hair loss among the less common symptoms of iron deficiency anaemia.

Can B12 deficiency cause numbness?

It can. The NHS lists pins and needles, and the NIH lists numbness or tingling in the hands and feet, among the symptoms of B12 deficiency; this is a sign of a nerve problem (NIH).

Is B12 deficiency the same as folate deficiency?

No, but they are similar. Both lead to abnormally large red blood cells that do not work properly and cause similar symptoms (NHS). According to the NHS, more than 1 mg of folic acid a day can hide the symptoms of B12 deficiency.

Should vegans take B12?

According to the NHS, because B12 is not found naturally in fruit, vegetables and grains, people on a vegan diet may not get enough. Ask your doctor or a dietitian what you need based on your diet.