Vitamin B12 deficiency occurs when a lack of vitamin B12 causes the body to produce abnormally large blood cells which can’t function properly.
Although uncommon, vitamin B12 deficiency can lead to complications with the nervous system, heart problems, pregnancy complications and birth defects, and temporary infertility.
People with severe anaemia are also at risk of developing heart failure.
There are various symptoms of the condition, one of which is a tingling or numb feeling in the hands, legs or feet.
The sensation could also be compared to pins and needles.
On top of this, other symptoms include difficulty walking, a swollen tongue, memory loss or difficulty thinking and reasoning, weakness and fatigue.
Vitamin B12 deficiency can be slow to develop, meaning symptoms can appear gradually and intensify over time.
It can, however, also come on relatively quickly.
Due to the array of symptoms, the condition can be confused with something else, but it can be confirmed by a blood test.
“It’s important for vitamin B12 or folate deficiency 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,” the NHS said.
As vitamin B12 is not made by the body, it must be sourced from food or supplements.
Food which is rich in B12 includes meat, fish, milk and dairy products, and eggs.
Non-meat and dairy sources include yeast extract, fortified breakfast cereals and soy products.
Supplements can also be taken, and injections or tablets provided for people whose deficiency is not diet-related.
Some people struggle to get enough B12 because, despite including it in their diet, their bodies are unable to absorb it.
This is especially relevant to people who have had weight-loss surgery.
Vitamin B12 deficiency is a relatively common condition, especially among older people.
“The human body needs vitamin B12 to make red blood cells, nerves, DNA, and carry out other functions,” said Patrick Skerrett at Harvard Health.
The average adult should get 2.4 microgrammes of B12 a day, according to Skerrett.
“It’s a good idea to ask your doctor about having your B12 level checked if you are a strict vegetarian or have had weight-loss surgery or have a condition that interferes with the absorption of food,” said Skerrett.