Vitamin B12 deficiency is caused by a lack of vitamin B12 in the body.
Vitamin B12 is essential in keeping the nervous system healthy.
A lack of B12 can cause the body to produce abnormally large red blood cells that can’t function properly.
This can cause a wide range of symptoms, including extreme tiredness, a lack of energy, pins and needles, mouth ulcers and a sore and red tongue.
It can also lead to muscle weakness, disturbed vision, psychological problems and problems with memory, understanding and judgement.
Vitamin B12 deficiency is most often caused by pernicious anaemia.
Pernicious anaemia is a condition in which the immune system attacks healthy cells in the stomach, preventing the body from absorbing vitamin B12 from food.
In this instance, vitamin B12 deficiency can be treated by having injections of the vitamin or taking tablets to replace the vitamins.
In less common cases, vitamin B12 deficiency can be caused by a lack of the vitamin in your diet.
According to the NHS, this is uncommon, but can occur in people who follow a vegan diet, fad diets, or have a generally poor diet for a long time.
The four best food sources of vitamin B12 are meat, fish, dairy products and eggs.
Salmon and cod are particularly good sources in the fish category.
If you are vegan or vegetarian, you can also find B12 in yeast extract like Marmite, some fortified breakfast cereals and soy products.
Check the nutrition labels while food shopping to see how much vitamin B12 different foods contain.
“Some people can develop a vitamin B12 deficiency as a result of not getting enough vitamin B12 from their diet,” said the NHS.
“A diet that includes meat, fish and dairy products usually provides enough vitamin B12, but people who don’t regularly eat these foods – such as those following a vegan diet or who have a generally very poor diet – can become deficient.”
“Stores of vitamin B12 in the body can last around two to four years without being replenished, so it can take a long time for any problems to develop after a dietary change.”
In addition to food sources of B12, people with diet-related vitamin B12 deficiency may also need to take tablets every day between meals until symptoms improve.
If vitamin B12 deficiency isn’t diet-related, B12 injections are usually required.
Injections may be administered every other day for two weeks until symptoms have improved, and then reduced to every three months.