A lack of B12 causes the body to produce abnormally large red blood cells which can’t function properly, which can cause anaemia.

Anaemia is the general term for having either fewer red blood cells than normal or having an abnormally low amount of haemoglobin in each red blood cell.

This can then lead to problems with the nervous system and heart conditions.

Our bodies don’t make vitamin B12, so it’s important to get it through a balanced diet.

Good sources of B12 include beef, pork, eggs, milk, cheese and fish.

However, it is possible to feed your body with B12 through injections of the vitamin.

According to the NHS, a B12 deficiency is usually treated with injections of the vitamin in a form called hydroxocobalamin.

Injections will be given every other day for two weeks, or until symptoms start improving.

After the initial two weeks, further treatment will depend on whether the cause of the deficiency is related to your diet.

However, the most common cause of a B12 deficiency is pernicious anaemia, which isn’t related to your diet.

If this is the case, you will usually need to have an injection of hydroxocobalamin every three months for the rest of your life.

If you’ve had neurological symptoms – symptoms that affect your nervous system, such as numbness or tingling in your hands and feet – caused by a vitamin B12 deficiency, you’ll be referred to a haematologist.

This may mean you need to have injections every two months. Your haematologist will then advise on how long you need to keep taking the injections.

If, on the other hand, your B12 deficiency is caused by a lack of the vitamin in your diet, you will be prescribed vitamin B12 tablets to take every day between meals.

Alternatively, you may need to have an injection of hydroxocobalamin twice a year.

Once your B12 levels have returned to normal and your diet has improved, you may be advised to stop taking the tablets.

People who struggle to include enough B12 in their diet, however, may have to take tablets for life.

Sources of vitamin B12, which are alternatives to meat and dairy products, are yeast extract, fortified breakfast cereals and soy products.

Symptoms of a vitamin B12 deficiency include: extreme tiredness, a lack of energy, pins and needles, mouth ulcers, a sore and red tongue, muscle weakness, disturbed vision, psychological problems and issues with memory, understanding and judgement.

“It’s important for vitamin B12 anaemia to be diagnosed and treated as soon as possible because, although many of the symptoms improve with treatment, some problems caused by the condition can be irreversible,” said the NHS.