Vitamin B12 overdose: Is it possible?
Vitamin B12 is essential, but is it possible to overdose on it? Here you can find out what causes high vitamin B12 levels and when you should consult a doctor.
Is it possible to overdose on vitamin B12?
Vitamin B12 is a water-soluble vitamin and is generally well tolerated.
It is absorbed by the body and part of it is stored in the liver so that your body can draw on it when needed.1
Excess amounts that your body does not need are usually excreted in the urine.
When taking dietary supplements or high-dose pharmaceuticals such as Vibe®*, no symptoms of overdose are known under normal intake conditions.1
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💡 Important to know: Blood levels vs. actual intake
If you take a lot of vitamin B12 (for example, in tablet form), the total B12 level measured in your blood will increase. However, this value only shows the total amount of vitamin B12 in your blood—not how much of it actually reaches your cells.
Why is that? Vitamin B12 is transported in the blood by various carrier proteins. Only part of it—the so-called active B12—can be absorbed and used by your cells. Although most of it is present in the blood, it is not directly available to your body. A high blood level does not automatically mean that your body has actually absorbed or stored too much vitamin B12. Your body simply excretes what it does not need in your urine.2,3,4
Note
Persistently high levels may be an indication of underlying conditions, such as liver or kidney disease.5 If this is the case, consult your doctor, especially if the levels remain high over a longer period of time or if you are not taking any supplements.
Intake and blood levels
It is important to distinguish between the amount consumed and the blood level, because the two do not mean the same thing.
intake
There are no known cases of overdose when taking dietary supplements or high-dose vitamin B12 medications.1 Even 1000 µg daily is often used in therapy and is considered well tolerated. However, the dose should always be appropriate for your situation and supervised by a doctor.
blood levels
High vitamin B12 levels do not automatically mean that you have taken too much. The total B12 value measured only shows how much B12 is present in your blood overall—not how much of it actually reaches your cells. This is because vitamin B12 is bound to various carrier proteins in the blood: only a portion (the active B12) can be absorbed by your cells. The majority circulates in the blood but is not directly available to the body and is excreted again.2,3,4
Sometimes, an elevated value can also be an important indication of health changes, for example in the case of liver or kidney dysfunction.5
Causes of high vitamin B12 levels
Elevated vitamin B12 levels in the blood are often an important indicator of certain diseases. Possible reasons for high levels include, for example:5
- Liver diseases in which the uptake or release of vitamin B12 is altered
- Kidney dysfunction affecting excretion via urine
- inflammatory processes in the body
- certain blood disorders that alter the blood count and vitamin B12 concentration
If your blood values remain elevated over a longer period of time without taking high-dose supplements, it is advisable to consult a doctor to determine the underlying causes.
Vitamin B12 levels too high – what to do?
High vitamin B12 levels usually go unnoticed. You don’t usually experience any clear symptoms – it can only be detected by a blood test.
If your lab results indicate elevated levels, these steps will help you:
Have your blood levels checked.
Talk to a doctor about the results. Only a medical evaluation can determine whether it is an overdose, a metabolic change, or another health issue.
Check your intake.
If you are taking high-dose vitamin B12 supplements, it may be advisable to reduce the dose or temporarily stop taking them—always in consultation with a doctor.
Rule out underlying conditions.
If you are not taking any medication, a high value may be an indication of liver, kidney, or blood disease.5 Your doctor can initiate appropriate tests to determine the exact cause.
Frequently asked questions about vitamin B12 deficiency
Is it possible to overdose on vitamin B12?
No symptoms of overdose are known under normal conditions of use.1 Vitamin B12 is water-soluble, and excess amounts are excreted in the urine.2,3,4 Only in certain diseases, such as liver or kidney disease, should intake be monitored by a doctor.5
How much vitamin B12 can you take daily?
To treat a deficiency, 1000 µg of vitamin B12 is often taken daily and is considered easy to tolerate. The right dose depends on what you need it for and what your doctor says. Higher blood levels don’t automatically mean you’ve taken too much.2,3,4
What to do if your vitamin B12 level is too high?
Discuss your blood values with a doctor. If you are taking vitamin B12 supplements, it may be advisable to adjust the dosage. Without supplements, elevated values should be checked by a doctor to rule out any underlying conditions.
*Vibe® is a vitamin B12 supplement used to treat a specific type of anemia. It is used in adults for the long-term treatment of anemia caused by vitamin B12 deficiency (called pernicious anemia) after blood levels have been brought back to normal through treatment with vitamin B12 injections.
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1 Vasavada, Advait, u. a. „Cyanocobalamin“. StatPearls, StatPearls Publishing, 2025.
2 Nexo, Ebba, und Elke Hoffmann-Lücke. „Holotranscobalamin, a Marker of Vitamin B-12 Status: Analytical Aspects and Clinical Utility“. The American Journal of Clinical Nutrition, Bd. 94, Nr. 1, 2011, S. 359S-365S, doi:10.3945/ajcn.111.013458.
3 Al Aisari, Faiza, u. a. „Comparison between Serum Holotranscobalamin and Total Vitamin B12 as Indicators of Vitamin B12 Status“. Oman Medical Journal, Bd. 25, Nr. 1, 2010, S. 9–12, doi:10.5001/omj.2010.3.
4 Dastidar, Rinini, und Kunal Sikder. „Diagnostic Reliability of Serum Active B12 (Holo-Transcobalamin) in True Evaluation of Vitamin B12 Deficiency: Relevance in Current Perspective“. BMC Research Notes, Bd. 15, Nr. 1, 2022, S. 329, doi:10.1186/s13104-022-06224-8.
5 Park, Jaesik, u. a. „Predictive Role of Vitamin B12 in Acute Kidney Injury in Living Donor Liver Transplantation: A Propensity Score Matching Analysis“. BMJ Open, Bd. 10, Nr. 11, 2020, S. e038990, doi:10.1136/bmjopen-2020-038990.
