Vitamin B12 deficiency and pernicious anaemia

What is vitamin B12 deficiency?

Vitamin B12 deficiency occurs when a person has insufficient vitamin B12. Vitamin B12, also known as cobalamin, is a vitamin that plays a crucial role in various bodily functions. It’s an essential nutrient that the body needs but cannot produce on its own, so it must be obtained through diet or supplements.

Vitamin B12 is primarily involved in the production of red blood cells, the maintenance of a healthy nervous system, including brain function, and releasing energy from food. Vitamin B12 deficiency anaemia occurs when a lack of vitamin B12 causes the body to produce abnormally large red blood cells that cannot function properly. Folate deficiency causes the same type of anaemia.

Vitamin B12: What is it?

Vitamin B12 is essential for life. It is needed to make new cells in the body, such as the many new red blood cells which are made every day. Vitamin B12 is found in meat, fish, eggs and milk - but not in fruit or vegetables.

How much vitamin B12 do I need per day?

Adults (aged 19 to 64) need about 1.5 micrograms a day of vitamin B12. The recommendations for ages 1 to 18 are:

• Aged 1 to 3 years: 0.5 micrograms a day.

• Aged 4 to 6 years: 0.8 micrograms a day.

• Aged 7 to 10 years: 1.0 micrograms a day.

• Aged 11 to 14 years: 1.2 micrograms a day.

• Aged 15 to 18 years: 1.5 micrograms a day.

If you eat meat, fish or dairy foods, you should be able to get enough vitamin B12 from your diet. But as vitamin B12 is not found naturally in foods such as fruit, vegetables and grains, vegans may not get enough of it.

Although body stores of vitamin B12 are sufficient to last for 2–5 years, vitamin B12 deficiency is common.

Foods containing vitamin B12

Good sources of vitamin B12 include meat, fish, milk, cheese, eggs, and some fortified breakfast cereals.

Vitamin B12 deficiency symptoms

Cells in different parts of the body may be affected if you lack vitamin B12.

Symptoms due to anaemia

These are caused by the reduced amount of oxygen in the body. Common symptoms include:

• Tiredness.

• Lethargy.

• Sore mouth and tongue.

• Feeling faint.

• Becoming breathless.

Less common symptoms include:

• Headaches.

• A 'thumping heart' (palpitations).

• Shortness of breath.

• Altered taste.

• Loss of appetite.

• Ringing in the ears (tinnitus).

• You may look pale.

Other effects of B12 deficiency

If left untreated, problems with the nervous system and psychological problems can develop. Psychological problems may include depression, confusion, and difficulty with memory, or even dementia. Neurological symptoms may include numbness, pins and needles, vision changes and problems with balance.

What causes vitamin B12 deficiency?

Pernicious anaemia

Normally, when you eat foods with vitamin B12, the vitamin combines with a protein called intrinsic factor in the stomach. Intrinsic factor is essential to absorb vitamin b12 into the body.

The combined vitamin B12/intrinsic factor is absorbed into the body further down the gut at the end of the small intestine. Intrinsic factor is made by cells in the lining of the stomach and is needed for vitamin B12 to be absorbed. If the body does not absorb enough vitamin B12 then this causes various health problems, including anaemia. This type of anaemia is called pernicious anaemia.

Pernicious anaemia is classified as an autoimmune disease. The immune system normally makes antibodies to attack bacteria, viruses and other germs. If you have an autoimmune disease, the immune system makes antibodies against certain tissues of your body.

If you have pernicious anaemia, antibodies are formed against your intrinsic factor, or against the cells in your stomach which make intrinsic factor.

This stops intrinsic factor from attaching to vitamin B12, so the vitamin cannot be absorbed into your body. It is thought that something triggers the immune system to make antibodies against intrinsic factor. The trigger is not known.

Pernicious anaemia usually develops over the age of 50. Women are more commonly affected than men and it tends to run in families. It occurs more commonly in people who have other autoimmune diseases. For example:

• Thyroid diseases.

• Addison's disease.

• Vitiligo (a condition where white patches develop on the skin).

The antibodies which cause pernicious anaemia can be detected by a blood test to confirm the diagnosis.

Stomach or gut problems

Various problems of the stomach or gut can be a cause of vitamin B12 deficiency. They are all uncommon causes. They include:

• Surgery to remove the stomach (including weight loss surgery) or the end of the small intestine. This will mean absorption of vitamin B12 may not be possible.

• Some diseases that affect the end of the small intestine where vitamin B12 is absorbed may affect the absorption of the vitamin - for example, Crohn's disease.

• Some conditions of the stomach may affect the production of intrinsic factor which is needed to combine with vitamin B12 to be absorbed - for example, autoimmune gastritis.

Recreational use of nitrous oxide

Recreational use of nitrous oxide gas can cause vitamin B12 deficiency. Recreational use of nitrous oxide has increased rapidly in recent years and is now the second most commonly used recreational drug among young people in the UK. Treatment with vitamin B12 (see below) does not work unless the person stops using nitrous oxide as a recreational drug.

Medicines

Certain medicines used for other conditions may affect the absorption of vitamin B12. These include:

• Colchicine.

• H2-receptor antagonists.

• Metformin.

• Phenobarbital.

• Pregabalin.

• Primidone.

• Proton pump inhibitors.

• Topiramate.

Dietary causes

It is unusual to lack vitamin B12 if you eat a normal balanced diet. Strict vegans who consume no animal or dairy products may not eat enough vitamin B12.

Foods that contain vitamin B12

Good sources of vitamin B12 include meat, fish, milk, cheese, eggs and food fortified with vitamin B12 (eg, some soy products, breakfast cereals and some breads).

How is vitamin B12 deficiency diagnosed?

The initial blood tests will include a full blood count (FBC) to see whether you are anaemic. The full blood count test will also include a level called the mean cell volume (MCV), which is raised with vitamin B12 deficiency but also in some other conditions.

The vitamin B12 level can be measured by a blood test. However some people may have symptoms of vitamin B12 deficiency despite normal vitamin B12 blood test results, or may have low blood levels despite having no symptoms. Therefore, the results of these blood test need to be interpreted together with your symptoms.

The commonly used blood test for vitamin B12 measures the total amount of vitamin B12 in your blood. This includes "active" forms of vitamin B12 that can be used by your body, as well as the "inactive" forms, which cannot be used.

Therefore, if a significant amount of the vitamin B12 in your blood is inactive, a blood test may show that you have normal vitamin B12 levels, even though you have vitamin B12 deficiency because of insufficient "active" vitamin B12. Blood tests that only measure the amount of vitamin B12 in your blood that is "active" are not yet widely available.

Further tests are then needed to find out the cause of the vitamin B12 deficiency. These further tests include blood tests for intrinsic factor antibodies and gastric parietal cell antibodies. These blood tests help to find out whether you have pernicious anaemia.

Vitamin B12 deficiency treatment

Any specific cause of vitamin B12 deficiency must be addressed, eg, improving diet to increase vitamin B12 intake, stopping or changing any medicine that is causing vitamin B12 deficiency, or stopping recreational use of nitrous oxide.

Vitamin B12 can be given either as supplements (by mouth) or by giving vitamin B12 injections. Whether tablets or injections are needed will depend on the cause of the vitamin B12 deficiency and whether there are any complications, such as anaemia or nerve problems.

The length of time that treatment is required will also depend on the cause. If you have pernicious anaemia the treatment is needed for life. However, if the cause is diet-related or caused by a medicine then the treatment may be stopped once the cause has been addressed and body stores of vitamin B12 are back to normal.

The injections are usually given frequently at the start of treatment. This quickly builds up the body's store of vitamin B12. Vitamin B12 is stored in the liver. Once a store of vitamin B12 has built up, this can supply the body's needs for several months.

Apart from the discomfort of having an injection, you should have no side-effects from the treatment. The injections are simply replacing a vitamin that you need.

Read more in the separate leaflet called Diets suitable for people with anaemia.

Follow-up

The symptoms of anaemia usually start to improve within a few weeks once treatment has begun. You may be advised to have a blood test every year or so. This will check that the anaemia is being treated successfully. A blood test may also be done to see that your thyroid gland is working well. (Thyroid problems are more common in people with pernicious anaemia.)

Any psychological or nerve problems caused by vitamin B12 deficiency may take a long time to treat and may not fully resolve with treatment. Prolonged or severe vitamin B12 deficiency may therefore cause permanent brain or nerve damage.

If you have pernicious anaemia, you are about three times more likely to develop stomach cancer than someone without pernicious anaemia, even when the anaemia is treated. See a doctor soon if you develop any stomach symptoms such as indigestion or stomach pain.

Frequently asked questions

Can you overdose on vitamin B12?

There's not enough evidence to show what the effects may be of taking excessive doses of vitamin B12 supplements each day.

Can vitamin B12 deficiency be a sign of cancer?

There is currently no evidence to suggest that vitamin B12 deficiency is a sign of any type of cancer. However, people with autoimmune gastritis (pernicious anaemia) have an increased risk of getting stomach cancer.

How long to recover from vitamin B12 deficiency?

The usual response to treatment can vary and depends on the cause of the vitamin B12 deficiency. Symptoms may start to improve within 2 weeks of being diagnosed and treated, but improvement may take up to 3 months. It can take much longer for symptoms to disappear altogether. Symptoms may get worse initially during treatment.