Vitamin B12 performs a number of essential roles in the body, such as supporting red blood cell formation and the healthy maintenance of the nervous system. Stripped of B12, these mechanisms stop performing and may undergo irreversible damage. There are a wide range of ways you may be alerted to low levels of B12.
A case report published in The New England Journal of Medicine highlights the range of possible symptoms: "Over the course of two months, a 62-year old man developed numbness and a ‘pins and needles' sensation in his hands, had trouble walking, experience severe joint pain, began turning yellow, and became progressively short of breath."
As Harvard Health points out, this case report does not capture the full list of symptoms, however.
In addition to deep depression, paranoia and delusions, memory loss, and incontinence, loss of taste and smell has also been observed in patients with low B12 levels.
The link to loss of smell is attributed to the damage B12 deficiency inflicts on the nervous system.
Pernicious anaemia prevents the body from making intrinsic factor - a protein made by the stomach and needed to absorb vitamin B12 in the intestine.
The other common cause is insufficient dietary intake - this exclusively applies to people following a strict vegan or vegetarian diet.
Vitamin B12 is found naturally in a wide variety of animal foods, such as beef liver and clams, which are the best sources of vitamin B12, according to the National Institutes of Health (NIH).
If you're a vegetarian or vegan, you can find B12 in a number of alternative sources, however.
As the NHS explains, yeast extract (including Marmite), as well as some fortified breakfast cereals and soy products contain B12.
"Check the nutrition labels while food shopping to see how much vitamin B12 different foods contain," adds the health body.How to treat B12 deficiency
The treatment for vitamin B12 or folate deficiency anaemia depends on what's causing the condition.
Vitamin B12 deficiency anaemia is usually treated with injections of vitamin B12.
There are two types of vitamin B12 injections:HydroxocobalaminCyanocobalamin
"If your vitamin B12 deficiency is caused by a lack of the vitamin in your diet, you may be prescribed vitamin B12 tablets to take every day between meals," explains the NHS.
According to the health body, people who find it difficult to get enough vitamin B12 in their diets, such as those following a vegan diet, may need vitamin B12 tablets for life.
It adds: "If you have had neurological 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 and may need to have injections every two months."