Vitamin B12 excess: Why does it occur and what are the consequences?

Content Table

exceso de vitamina B12 abstract

In numerous blog articles we have talked about the importance of vitamin B12 in our health. You already know that it is essential to ingest an adequate amount of this vitamin and, above all, special attention must be paid in those situations where there may be a deficit, as is the case of vegetarian and vegan diets.

But this time we are going to talk about the opposite of vitamin B12 deficiency: vitamin B12 excess or B12 hypervitaminosis.

How vitamin B12 is absorbed and transported

To understand why excess vitamin B12 can occur, it is first necessary to understand the mechanism of absorption and transport of this vitamin.

Vitamin B12 is absorbed in the last part of the small intestine, specifically in the ileum.
. In order for vitamin B12 to be absorbed and reach plasma, it needs to bind to the intrinsic factor. Once it is absorbed and passes into the bloodstream, it travels bound to haptocorrin and transcobalamin. There are three types of transcobalamins, the most common being the
or transcobalamin II, which is the most relevant because it is the biologically active
biologically active fraction

Why does excess vitamin B12 occur?

Vitamin B12 can be stored in the liver for long periods of time to avoid deficiencies.

It is a
water-soluble vitamin
The excess can be eliminated in urine if there is no health problem. However, there are some pathologies in which we can have vitamin B12 in excess:

  • Increased vitamin B12 transporter proteins
    proteins in neoplasms
    (liver, breast, colon, stomach and pancreatic cancer).

  • Abundant
    release of reserved vitamin B12 in the liver
    Decreased synthesis of holotranscobalamin
    liver disease

  • Renal disease
    causing decreased filtration of holotranscobalamin.

  • Autoimmune diseases
    Systemic lupus erythematosus, rheumatoid arthritis, etc.

In addition, the
very high intakes
Vitamin B12 deficiency can also lead to hypervitaminosis. This is more rare, but can occur if we consume supplements or use vitamin B12 injectables at very high doses and for long periods of time.

High levels of vitamin B12 may be a warning sign of an elevated risk of
high risk of developing neoplasms.
. Hypervitaminosis of vitamin B12 can be an important cause of
nonspecific tumor marker
once other pathologies such as hematological, hepatic and renal diseases have been ruled out.

The symptoms of hypervitaminosis are nonspecific and variable: nausea, vomiting, headache, insomnia or blurred vision.

In case of vitamin B12 deficiency, there are clinical guidelines, such as the intake of a complete vitamin B12 supplement. However, there are no specific treatments for hypervitaminosis, but it is necessary to know what it is due to and to act soon because it can be a serious disease.


  • García-Rodríguez AM et al. Is hypervitaminosis B12 a tumor predictor? Rev Mx Med Fam. 2020;7:7-15.

  • Sánchez-Duque JA et al. Hypervitaminosis B12: a look from primary care. Semergen: revista española de medicina de familia, ISSN 1138-3593, Nº. 1, 2021, pp. 67-68.

  • Zulfiqar A et al. Hypervitaminosis B12. Our experience and a review. Medicine – Volume 79 – No. 5, 2019.

Elena García-Maldonado


Latest Articles

Send Me News

NewsLetter ES
Acepto la politica de recogida de datos
El propósito de este formulario es recibir respuesta a su consulta.
El responsable de almacenar sus datos es Laboratorios Zamdeh, S.L.
En cualquier momento puede cancelar su suscripción