Vitamin B12

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is essential for various metabolic processes, the production of red blood cells, and the maintenance of healthy nerve function. It is unique among vitamins, as it contains a cobalt ion at its centre, making it the only vitamin containing a metal ion.


The history of vitamin B12 is closely tied to the discovery of pernicious anaemia, a type of megaloblastic anaemia caused by an inability to absorb vitamin B12 from the gastrointestinal tract. In the late 19th and early 20th centuries, scientists and physicians began to recognise the connection between a deficiency of an unknown factor in the diet and the development of pernicious anaemia.

In the 1920s, American physicians George Whipple, George Minot, and William Murphy discovered that feeding raw liver to anaemic dogs could reverse the symptoms of anaemia. Subsequent research by these scientists and others led to the identification of the “anti-pernicious anaemia factor” present in liver extracts. Whipple, Minot, and Murphy were awarded the Nobel Prize in Physiology or Medicine in 1934 for their discoveries related to the treatment of anaemia with liver extracts.

Vitamin B12 was finally isolated from liver extracts in 1948 by two independent research groups: one led by Karl Folkers at Merck Laboratories in the United States, and the other led by Alexander Todd in the United Kingdom. The chemical structure of vitamin B12 was determined in 1956 by chemist Dorothy Crowfoot Hodgkin, who later received the Nobel Prize in Chemistry in 1964 for her work on the structure of important biochemical substances, including vitamin B12.

Vitamin B12 is primarily found in animal-based foods, such as meat, poultry, fish, eggs, and dairy products. As a result, vegetarians and vegans are at a higher risk of developing a vitamin B12 deficiency and may need to consume fortified foods or supplements to maintain adequate levels.

The absorption of vitamin B12 is a complex process that requires a protein called intrinsic factor, which is secreted by cells in the stomach. Intrinsic factor binds to vitamin B12, allowing it to be absorbed in the small intestine. Some individuals may have an impaired ability to produce intrinsic factor, leading to pernicious anaemia and the need for alternative methods of B12 supplementation, such as injections or high-dose oral supplements.

Functions Of Vitamin B12

Vitamin B12, or cobalamin, is an essential nutrient that plays a crucial role in several key biological processes within the body. Some of the primary functions of vitamin B12 include:

  • Red blood cell production: Vitamin B12 is necessary for the proper formation of red blood cells, which carry oxygen throughout the body. A deficiency in vitamin B12 can lead to pernicious anaemia, a type of megaloblastic anaemia characterised by abnormally large and immature red blood cells.
  • DNA synthesis: Vitamin B12 plays a critical role in DNA synthesis and repair, which is essential for cell division and growth.
  • Nervous system function: Vitamin B12 is vital for the maintenance of the myelin sheath, a protective layer that surrounds nerve fibres and ensures the proper transmission of nerve impulses. A deficiency in vitamin B12 can lead to neurological issues, such as numbness, tingling, and weakness in the limbs, as well as cognitive impairments.
  • Homocysteine metabolism: Vitamin B12, along with vitamins B6 and B9 (folate), is involved in the metabolism of homocysteine, an amino acid. Elevated levels of homocysteine have been associated with an increased risk of cardiovascular disease.
  • Energy production: Vitamin B12 plays a role in energy production within cells, as it is involved in the conversion of food into energy (in the form of adenosine triphosphate, or ATP) through its participation in various metabolic pathways.
  • Synthesis of neurotransmitters: Vitamin B12 is involved in the synthesis of certain neurotransmitters, such as serotonin and dopamine, which are important for mood regulation and brain function.

Good Sources Of Vitamin B12

Vitamin B12 is primarily found in animal-based foods. Some good sources of vitamin B12 include:

  • Meat: Beef, pork, lamb, and liver are rich sources of vitamin B12. Liver, in particular, contains very high amounts of B12.
  • Poultry: Chicken, turkey, and other poultry products are good sources of vitamin B12.
  • Fish: Fatty fish such as salmon, tuna, trout, sardines, and herring, as well as shellfish like clams, mussels, and crab, are excellent sources of vitamin B12.
  • Dairy products: Milk, cheese, yogurt, and other dairy products contain significant amounts of vitamin B12.
  • Eggs: While not as high in B12 as some other sources, eggs do provide a moderate amount of vitamin B12, particularly in the yolk.

For vegetarians and vegans, obtaining sufficient vitamin B12 from dietary sources can be more challenging since plant-based foods generally do not contain significant amounts of B12. However, there are some options available:

  • Fortified foods: Certain plant-based foods are fortified with vitamin B12, such as plant milks (soy, almond, oat, etc.), breakfast cereals, nutritional yeast, and meat substitutes. Check the labels to find products with added vitamin B12.
  • Supplements: Vegetarians and vegans may need to consider taking a vitamin B12 supplement to ensure they are getting enough of this essential nutrient.

It’s important to note that the bioavailability of vitamin B12 in supplements and fortified foods may vary. Therefore, it is crucial to monitor your vitamin B12 levels and consult with a healthcare professional to determine the appropriate supplementation, if necessary. For more information, please read the following article:

How Much Vitamin B12 Do We Need?

The Dietary Reference Intakes (DRIs) for vitamin B12 provided by the NIH are as follows:

  • Infants (0-6 months)*: 0.4 mcg/day (micrograms)
  • Infants (7-12 months)*: 0.5 mcg/day
  • Children (1-3 years): 0.9 mcg/day
  • Children (4-8 years): 1.2 mcg/day
  • Children (9-13 years): 1.8 mcg/day
  • Teens (14-18 years): 2.4 mcg/day
  • Adults (19 years and older): 2.4 mcg/day
  • Pregnant women: 2.6 mcg/day
  • Breastfeeding women: 2.8 mcg/day

*For infants, the values provided are Adequate Intakes (AI) rather than DRIs, as there is not enough data to establish DRIs for this age group.

These values are general guidelines, and individual needs may vary depending on factors such as overall health, lifestyle, and dietary choices. It is essential to consume adequate amounts of vitamin B12 through a balanced and varied diet or supplementation if necessary. If you are concerned about your vitamin B12 intake, consult with a healthcare professional for personalised advice.

What Are The Signs Of Vitamin B12 Deficiency?

Vitamin B12 deficiency can lead to various symptoms, as it plays a vital role in the production of red blood cells, DNA synthesis, and maintaining healthy nerve function. Some of the signs and symptoms of vitamin B12 deficiency include:

  • Fatigue and weakness: As a result of decreased red blood cell production and reduced oxygen-carrying capacity, individuals with vitamin B12 deficiency often experience fatigue, weakness, and lethargy.
  • Pale or yellowish skin: Due to the impaired production of red blood cells, a person with vitamin B12 deficiency may develop pale or yellowish skin, known as jaundice.
  • Glossitis and mouth ulcers: Inflammation of the tongue (glossitis), a swollen, smooth, red tongue, and mouth ulcers can be signs of B12 deficiency.
  • Megaloblastic anaemia: Vitamin B12 deficiency can lead to megaloblastic anaemia, characterised by abnormally large and immature red blood cells, which can cause additional symptoms such as shortness of breath and dizziness.
  • Numbness and tingling: A deficiency in vitamin B12 can lead to nerve damage, causing sensations of numbness, tingling, or “pins and needles” in the hands and feet.
  • Balance and coordination problems: Severe vitamin B12 deficiency can affect the nervous system, leading to issues with balance, coordination, and muscle weakness.
  • Cognitive issues: Vitamin B12 deficiency can contribute to cognitive problems such as memory loss, difficulty concentrating, confusion, and even dementia in severe cases.
  • Mood disturbances: B12 deficiency has been linked to mood changes, depression, and irritability.
  • Visual disturbances: In some cases, vitamin B12 deficiency can affect the optic nerve, leading to blurred or disturbed vision.

If you suspect you have a vitamin B12 deficiency, it is essential to consult with a healthcare professional for proper diagnosis and treatment. Blood tests can help determine your B12 levels, and treatment may include dietary changes, oral supplements, or B12 injections, depending on the severity of the deficiency and its underlying cause.

What Happens If I Take Too Much Vitamin B12?

Vitamin B12 is a water-soluble vitamin, which means that any excess is typically excreted through urine, making the risk of toxicity from overconsumption relatively low. There is no established tolerable upper intake level (UL) for vitamin B12, as it has a very low potential for toxicity.

However, it’s essential to note that taking very high doses of vitamin B12, particularly through supplements or injections, can sometimes cause side effects or adverse reactions in some individuals. Some possible side effects of excessive vitamin B12 intake include:

  • Skin reactions: High doses of vitamin B12 may cause acne, skin flushing, or rashes in some people.
  • Headaches and dizziness: Some individuals might experience headaches or dizziness after taking large amounts of vitamin B12.
  • Anxiety and nervousness: In rare cases, excessive vitamin B12 intake may cause increased anxiety or nervousness.
  • Nausea and diarrhoea: large doses of vitamin B12 can sometimes cause gastrointestinal side effects, such as nausea, diarrhoea, or upset stomach.

Although vitamin B12 toxicity is rare, it is essential to follow the recommended dietary allowances (RDAs) and consult with a healthcare professional before taking high-dose supplements, especially if you have any pre-existing health conditions or are taking other medications.