What is vitamin B12?

Also known as cobolamin, Vitamin B12 is a water-soluble vitamin which plays a role in the normal functioning of the human body, in particular the brain and nervous system.

The way B12 does this is through the synthesis of myelin, the material which forms an electrical insulator around the axon (the tail bit) of our nerve cells.

Where does vitamin B12 come from?

In short, animal products. Vitamin B12 is derived from animal sources such as meat, fish and dairy products.

The Western diet consists of a daily intake of around 5-30µg with between 1 and 5µg being absorbed.

In the UK, the government suggests a daily intake of 1.5µg. Our bodies store around 1-5mg of vitamin B12 therefore depletion of the nutrient can take years to become evident.

Some examples of Vitamin B12 sources include:


  • Clams
  • Haddock
  • Tuna
  • Salmon


  • Liver
  • Beef
  • Chicken

Dairy Products

  • Cheese
  • Milk
  • Yoghurt

With our main dietary sources of B12 deriving from animal products, vegetarians and vegans are at an increased risk of deficiency.

What are symptoms of vitamin B12 deficiency?

When vitamin B12 is deficient in our bodies there is usually a manifestation of symptoms affecting all different systems in the body.

These symptoms can include:

  • Extreme tiredness
  • Lack of energy
  • Mouth ulcers
  • Sore tongue
  • Pins and needles
  • Depression
  • Confusion
  • Memory problems

Therefore, these symptoms are mainly associated with the blood and nervous systems due to the vital role vitamin B12 plays within them.

What Causes Vitamin B12 Deficiency?

There are several reasons why Vitamin B12 can occur. As we mentioned earlier, it can take a number of years for the deficiency to become noticeable due to the stores we have in our body. Generally, once these stores begin to deplete, the symptoms of B12 deficiency will become noticeable.

Pernicious anaemia

One cause of Vitamin B12 deficiency is pernicious anaemia. The condition can cause malabsorption of B12 from both dietary sources and recycled biliary B12.

Pernicious anaemia is a result of autoimmune gastritis, a chronic inflammatory disease which affects the fundus and body of the stomach. In other words, the immune system attacks the cells in the stomach, preventing the absorption of Vitamin B12. In the UK, this is the number one cause of B12 deficiency.

At first pernicious anaemia may present with no symptoms at all but as time progresses the immune cells attack the stomach cells responsible for producing hydrochloric acid. At first it may be diagnosed as iron deficiency anaemia with a lack of gastric acid, which is required to digest iron.

However, progression over time leads to a reduced production of intrinsic factor, a requirement for the absorption of B12, which also coincides with a production of neutralising antibody against intrinsic factor. Therefore, as this continues B12 is no longer able to be absorbed and instead can lead to further complications such as megaloblastic anaemia and neurological difficulties.

Lack of dietary intake

A lack of intake of Vitamin B12 in the diet is also another cause for deficiency. Although, relatively uncommon it can leave several groups at risk of developing deficiency. For example:

  1. Strict vegan diets
  2. Fad diets
  3. Poor diets (e.g. elderly people who follow a tea and toast/biscuit diet)

As most of our dietary B12 comes from animal sources strict vegans and some vegetarians are at risk of developing Vitamin B12 deficiency. Other subgroups such as the elderly and those following lacto-ovo-vegetarian diets are also at risk.

Therefore, as there are few sources of B12 available to vegetarians and none available for vegans, these individuals must ensure they supplement their intake. This may also be true for the elderly, particularly as many may just adopt a tea and toast diet. The prevalence of Vitamin B12 deficiency in older people is relatively common; 1 in 20 aged 65-74 and 1 in 10 people over the age of 75.

Drugs and medication

There are some medications which can affect the amount of B12 the body absorbs. Some examples can include:

  1. Alcohol
  2. Nitrous oxide
  3. Metformin
  4. Proton pump inhibitors
  5. H2 receptor agonists


Metformin is an example of an antidiabetic drug used to treat type 2 diabetes and can also be used to treat polycystic ovary syndrome in women. In diabetic cases, it can lower blood sugar levels and improve the body’s handling of insulin. However, when it comes to Vitamin B12, Metformin can disrupt its absorption and contribute to B12 deficiency.

Proton pump inhibitors

Proton pump inhibitors (PPIs) are a type of medication administered to limit the amount of acid the stomach produces. They are commonly given to those who suffer from conditions such as acid reflux and stomach ulcers. Gastric acid is a necessary requirement to ensure the adequate absorption of Vitamin B12. Some studies have shown that long term use of PPIs is not linked to Vitamin B12 deficiency. Whereas, others studying long term use of high dose PPIs have shown some links between the reduction in the production of gastric acid with a reduced serum concentration of Vitamin B12.


Most cases of Vitamin B12 deficiency can be easily treated with B12 injections or oral supplements.

In most cases, injections are normally the first choice for treatment. If it is discovered that diet is the issue with B12, then regular oral supplements or injections will be administered between meals.

Vegans may have to receive oral supplements or injections for the rest of their life. Whereas, in other cases treatment may be short term. Another option is to improve the overall diet by increasing intake of vitamin B12 rich foods. There are some foods available which have been fortified with vitamins including B12. Examples can include breakfast cereals and soya products such as those sold as meat alternatives.


Vitamin B12 deficiency can be a serious condition if left untreated but it is often hard to recognise as its symptoms can be subtle. Manifestations can include neurological and dementia like symptoms as well as abnormal blood results.

Groups such as vegans and the elderly are most at risk from Vitamin B12 deficiency as well as those prescribed certain medications.

Supplementation of B12 either orally or through injections is the best way to treat the condition and if caught early enough some symptoms may be reversible.

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Having always been intrigued by how body’s work, both in their day to day functions and also when things go wrong, Leanne is pursuing her passion for health. By combining her undergraduate degree in Biomedical Science and a Masters in Science communication with her love for writing, she is passing on her knowledge to Health Hub readers. Leanne strongly believes that science and health are something that should be talked about more and she hopes her articles will enable such conversations.