From the Guidelines
Vitamin B12 overdose symptoms are extremely rare, but high doses may lead to nausea, anorexia, and mild ataxia, as well as increased urinary excretion, with no established upper limit for toxicity 1.
Overview of Vitamin B12 Overdose
Vitamin B12 is a water-soluble vitamin, and excess amounts are typically excreted through urine, reducing the risk of toxicity. However, high doses from supplements can cause side effects.
- The most common symptoms associated with high doses of vitamin B12 include nausea, anorexia, and mild ataxia, as reported in the espen micronutrient guideline 1.
- High intravenous doses have rarely led to anaphylaxis, highlighting the importance of cautious administration 1.
- Doses exceeding 400 mg may induce these symptoms, emphasizing the need for careful dosing and monitoring 1.
Clinical Considerations
In clinical practice, it is essential to be aware of the potential for vitamin B12 overdose, particularly in patients receiving high doses or intravenous administration.
- Monitoring for signs of toxicity, such as nausea, anorexia, and ataxia, is crucial in patients receiving high doses of vitamin B12 1.
- The absence of an established upper limit for toxicity underscores the importance of careful dosing and monitoring to minimize the risk of adverse effects 1.
- Other guidelines, such as those from the British Obesity and Metabolic Surgery Society, focus on the treatment of vitamin B12 deficiency rather than overdose, highlighting the different clinical considerations for deficiency versus excess 1.
From the Research
Symptoms of Vitamin B12 Overdose
Causes of Hypervitaminosis B12
- Excess of vitamin B12 intake 3
- Solid neoplasia (primary or metastatic) 3
- Acute or chronic hematological diseases 3
- Liver disorders 3
- Monoclonal gammapathy of undetermined significance 3
- Renal failure 3
- Inflammatory or autoimmune diseases 3
- Transient hematological disorders (neutrophilia and secondary eosinophilia) 3
Diagnosis and Treatment of Vitamin B12 Deficiency
- Screening may be warranted in patients with one or more risk factors, such as gastric or small intestine resections, inflammatory bowel disease, use of metformin for more than four months, use of proton pump inhibitors or histamine H2 blockers for more than 12 months, vegans or strict vegetarians, and adults older than 75 years 4
- Initial laboratory assessment should include a complete blood count and serum vitamin B12 level 4
- Measurement of serum methylmalonic acid should be used to confirm deficiency in asymptomatic high-risk patients with low-normal levels of vitamin B12 4
- Oral administration of high-dose vitamin B12 (1 to 2 mg daily) is as effective as intramuscular administration for correcting anemia and neurologic symptoms 4