Vitamin B12: Functions and Dangers of Deficit

How much do you know about vitamin B12? In our post today, read all about this micro-nutrient.
Vitamin B12: Functions and Dangers of Deficit

Last update: 04 November, 2019

Vitamin B12, also known as “Cobalamin”, is a water-soluble vitamin. It has a corrin ring structure and, as we’ll explain later in our post, is extremely important for the body– especially for vegans.

Types of vitamin B12

There are two groups of vitamin B12 that vary in form:

  • Physiological form: 5′-Deoxyadensosylocobalamin is the most commonly stored and we can find it in certain food sources. Methylcobalamin corresponds to its form in plasma.
  • Non-physiological forms: Hydroxocobalamin is the most common type present in food sources. It’s also commonly available as an injection. Cyanocobalamin, on the other hand, is more common as a supplement.

Functions of vitamin B12

Just like many other B group vitamins, B12 acts as a coenzyme. Some of its most important functions include:

  • Participates in important metabolic reactions: Succinyl-CoA is a mediator in the Krebs cycle and helps gather energy. It’s also crucial for producing the homocysteine-to-methionine conversion. When the body faces a vitamin B12-deficit, homocysteine builds up excessively and can indicate a heart problem.
  • Red blood cell synthesis and development.
  • Vitamin B12 is essential for DNA creation during cellular division. The cellular division must proceed quickly in order to duplicate DNA correctly. If the body lacks vitamin B12 or B9 (folic acid), or both, its cells won’t be able to duplicate DNA. Furthermore, as they’re unable to divide, the cells continue to grow and create megaloblasts, which are abnormally sized blood cells.
  • Keeping the nervous system healthy: vitamin B12 helps keeps the myelin sheath of neurons intact.
  • Synthesizing and producing neurotransmitters.
  • Synthesizing proteins and amino acids.
vitamin b12 functions

Vitamin B12 deficiency

While most people who suffer from a vitamin B12 deficiency follow vegetarian or vegan diets, the diet isn’t always the root of the problem. Low levels of vitamin B12 can lead to pernicious anemia, which is a type of megaloblastic anemia. Megaloblastic anemia refers to anemia where the red blood cells are enlarged.

Deficiencies arise as a result of intrinsic or secretion problems (which is referred to as an autoimmune cause). The intrinsic factor is essential for absorbing the vitamin via intestines.

But you have to approach deficiencies carefully, as consuming enough folic acid will cover up any symptoms of anemia.

As we mentioned earlier, some deficiencies don’t arise from the diet. For example:

  • Atrophic gastritis: the inflammation in the gastric mucosa walls fall to produce the intrinsic factor.
  • Antibodies that fight against the intrinsic factor.
  • Autoimmune diseases, such as Autoimmune Addison disease.
  • Crohn’s disease.
  • Gastric resection.
  • Ilium resection.
  • Pancreatic insufficiency.
  • Hypochlorhydria, or achlorhydria (low or no production of hydrochloric acid).
  • Alcoholism.
  • Consuming certain drugs such as omeprazole.
  • Bacterial overgrowth.
  • Achylia (lack of pepsin in gastric juices in addition to lack of hydrochloric acid).
  • Pediatric pernicious anemia as a result of genetic predisposition.
  • Advanced age is a risk factor. People older than 50 should take supplements as a preventative measure or have regular check-ups.


You might notice the following symptoms if you have a vitamin B12 deficiency:

  • Megaloblastic anemia.
  • Anorexia.
  • Glossitis.
  • Paresthesia.
  • Ataxia.
  • Disfunción neurológica.
  • Mental symptoms such as changes in personality, irritability, memory problems, depression, dementia, psychosis with hallucinations and paranoia.
  • Paranoid schizophrenia.
  • Optic nerve damage.

Vitamin B12 can lead to irreversible neurological damage, which is why an early diagnosis is crucial.

vitamin b12 symptomatology

How can you be sure that your vitamin B12 levels are okay?

A blood test that covers B12 plasma, homocysteine, and methylmalonic acid levels is the most thorough way to check if you have a deficiency or not. On the other hand, tests that solely check B12 levels are insufficient as they don’t differentiate between analogs and active B12.

B12 analogs have corrin ring structures that contain cobalt but lack the activity of the vitamin. They don’t act as active B12 and can trick tests into marking them as cobalamin. In light of that, be careful with algae and fermented food products. The best way to prevent any misreadings is undergoing a thorough test that’s tailored to you.

Vitamin B12 sources

Animal meat is the best source of this vitamin.  While some enriched vegetable-based products, analyze them carefully as many have high levels of sugar.


Vegans need vitamin B12 supplements as they don’t consume any kind of animal product. Vegetarians who allow themselves to eat eggs and dairy products should also seek supplements to be safe as they might consume insufficient levels of vitamins.

There are different types of vitamin B12 but being the safest and cheapest, cyanocobalamin is always a good recommendation. Hydroxocobalamin is sold by Optovite as an injection. If cyanocobalamin presents a risk for you, as it does with smokers, hydroxocobalamin can be a good option instead.

How much you should take depends on the type of vitamin and the consumer. In any case, you should always see a specialist (dietitian or nutritionist) for a plan that best caters to you.

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All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Carmel R. (2006). Cobalamin (Vitamin B-12). In: Shils ME, Shike M, Ross AC, Caballero B, Cousins RJ, eds. Modern Nutrition in Health and Disease. Philadelphia: Lippincott Williams & Wilkins; 2006:482-497
  • Dharmarajan TS. Approaches to vitamin B12 deficiency: early treatment may prevent devastating complications. Postgrad Med 2001; 110:99-105.
  • Carmel R. Clinical aspects of megaloblastic anemia. En: Hematology Clinical and Laboratory Practice. St. Louis Missouri: Moby Year Book Inc, 1993:437-59.
  • Norris J., Vitamin B12: Are you Getting It? Recuperado dentro del periodo comprendido entre el 15 de diciembre de 2014 y el 10 de enero de 2015, del sitio web de Jack Norris.

The contents of this publication are written for informational purposes. At no time do they facilitate or replace the diagnoses, treatments, or recommendations of a professional. Consult your trusted specialist if you have any doubts and seek their approval before beginning any procedure.