Article Series

  1. Vitamin B12
  2. Vitamin B12 Requirement
  3. Vegan Foods With Vitamin B12
  4. Vitamin B12 Overdose and Excess

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Vitamin B12 Overdose and Excess

Vitamin B12 Overdose and Excess
Table Of Contents
  1. Causes of Vitamin B12 Excess
  2. Excess of Vitamin B12: Symptoms
  3. Consequences of Excess Vitamin B12
  4. Excess Values
  5. Treatment

In normal cases, a short-term vitamin B12 overdose poses no danger of poisoning. According to scientists, the toxicity of cobalamin (vitamin B12) is minimal, practically nonexistent 1. This is because vitamin B12 is a water-soluble vitamin. Excess vitamin B12 is usually excreted through urine 2.

In medical terminology, an excess of vitamin B12 in the body is referred to as hypercobalaminemia.

According to a Swiss study, elevated vitamin B12 levels are often detected incidentally but with an increasing trend 3.

Causes of Vitamin B12 Excess

Aside from overdosing on frequent use of supplements, an accumulation of vitamin B12 in the blood can occur in sick individuals. The accumulation of vitamin B12 in the blood can be attributed to various causes 4 5 6 7 8 9 10:

  • Chronic myeloid leukemia
  • Promyelocytic leukemia
  • Polycythemia
  • Autoimmune diseases like systemic lupus
  • Hypereosinophilic syndrome
  • Bronchopulmonary dysplasia (chronic lung disease)
  • Alcoholism
  • Neoplasia (proliferation of body tissues)
  • Liver diseases like hepatitis, cirrhosis, hepatocellular carcinoma, liver tumors, and liver cancer
  • Kidney damage
  • Gaucher's disease
  • Rheumatoid arthritis / Still's disease

An overdose primarily occurs in healthy vegans due to improper use of vitamin B12 supplements and injections. Nonetheless, an overdose is very rare even in these cases since very little vitamin B12 from supplements is absorbed by the body. Information on how a good B12 supplementation with appropriate dosages can be done is available here.

Excess of Vitamin B12: Symptoms

No upper limit for daily intake of B12 has been issued by health organizations. However, this does not mean that excessive intake of vitamin B12 cannot lead to toxic reactions. In rare cases, allergic reactions such as acne may occur 11 12.

Specific symptoms of vitamin B12 poisoning do not exist as hypercobalaminemia is accompanied by conditions such as kidney failure, liver diseases, and infections 13.

Non-specific symptoms of vitamin B12 excess may include 14:

  • Fatigue
  • Weight loss

Consequences of Excess Vitamin B12

Scientists associate high serum levels of vitamin B12 with increased mortality in critically ill patients 15.

According to other scientists, a high serum cobalamin level can be associated with an increased risk of mortality, especially in older people 16 17.

Vitamin B12 is essential for growth and cell division. Uncontrolled growth and cell division can lead to cancer. Studies from 2013 suggest that elevated levels of cobalamin in the body can be an indicator of cancer. 18 19. Older studies have shown a correlation between elevated B12 levels and prostate cancer. 20. Furthermore, cancer patients with higher B12 levels are at a higher risk of mortality compared to patients with normal levels. 21.

Excess Values

High serum vitamin B12 levels are considered to be in the range of 350 to 1,200 pmol/l (474.25 to 1,626.02 pg/ml) 22. Values above 600 pmol/l (813 pg/ml) are considered unexpectedly high 23. An investigation into the underlying causes and appropriate treatment should be initiated at the latest at this level.


Early detection of excess levels is of great importance for the subsequent course of the disease. Depending on the cause, the treating physician can initiate the appropriate therapy.