Is It OK To Take 1000 mcg of Vitamin B12 a Day?

Is It OK To Take 1000 mcg of Vitamin B12 a Day?

The daily dose of 1 mg (1000 mcg) oral cobalamin has shown good long-term results; the possibility of intermittent maintenance guidelines is investigated.
Vitamin B12 or cobalamin plays a key role as a coenzyme in DNA synthesis and cell maturation, as well as in the synthesis of neuronal lipids. The human organism is not able to synthesize it and must obtain it from the diet, mainly from foods of animal origin (meat, milk and derivatives, eggs, fish).

The vitamin ingested in the diet is separated from animal proteins by pepsin and gastric hydrochloric acid, joining haptocorrin, a protein of salivary origin, which is dissociated in the duodenum by the action of pancreatic proteases. It is absorbed in the distal ileum, after passing through the small intestine linked to the intrinsic factor (IF), a protein synthesized in the parietal cells of the gastric fundus. The B12-FI complex binds to the ileal cell receptors and is absorbed by endocytosis. Vitamin B12 passes into the bloodstream bound to transcobalamin II, which transports it to the liver and other areas of the body.

It is important to note that, apart from this mechanism, between 1 and 2% of the B12 ingested is absorbed by passive diffusion, regardless of the IF, of the integrity of the distal ileum or of the existence of gastric alterations or selective malabsorption of cobalamin.

More than 75% of the cobalamin excreted by bile is reabsorbed. Its urinary elimination is usually low.

The daily requirements of vitamin B12 are approximately 2 to 2.5 μg, provided in a balanced diet. The tissue stores of B12 are wide, between 3 and 10 mg, and can take decades to empty.

B12 Deficiency Causes

The main causes of vitamin B12 deficiency can be divided into three groups: low exogenous intake, poor digestion and malabsorption of the vitamin. The first occurs in strict vegetarians.

The pathologies most frequently associated with poor digestion of B12 are atrophic gastritis (related or not to Helicobacter pylori), achlorhydria and gastrectomy. Regarding the causes of malabsorption, it is worth mentioning pernicious anemia, a classic example of megaloblastic anemia, in which the parietal cells are destroyed by autoantibodies, producing an IF deficiency that leads to insufficient absorption of cobalamin. The resection of the ileum or ileal diseases may also cause malabsorption.

Treatment For Vitamin B12 Deficiency

The administration of vitamin B12 to correct or prevent the deficiency is usually for life, and has traditionally been prescribed in the form of intramuscular injections. The most usual regimen consists of daily doses of 1,000 μg for one week, followed by weekly injections for 4 weeks and, then, monthly. This treatment does not usually produce adverse effects, but it involves repeated visits, discomforts and risks in relation to the use of the parenteral route.

There is abundant accumulated evidence that the replacement of B12 can be carried out effectively orally. Several studies have shown that the small percentage (1-2%) of vitamin that is passively absorbed in the intestine could be sufficient to achieve, with high doses of vitamin B12, adequate concentrations in the body, even in cases of absence of IF by pernicious anemia or gastrectomy, achlorhydria, malabsorption or lack of integrity of the terminal ileum. Thus, if the daily needs of B12 are approximately 2 μg, administering oral supplements at high doses (1-2 mg) once a day can achieve a sufficient amount to ensure the values and filling of the tissue stores through passive intestinal absorption. Adverse effects to overdosage of vitamin B12 have not been reported. The oral treatment avoids the complications inherent to the injection and also relative contraindications, such as anticoagulation. It is only contraindicated in patients with inability to take oral medication or who present vomiting or diarrhea.


As with any other medication, it is necessary to ensure the adherence of the patient, supposedly more uncertain than with the monthly visits for the administration of the injectable.

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Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:July 23, 2018

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