Can you have too much B12?

Vitamin B12 Overdose - Is It Dangerous?

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Vitamin B12 tablets Image: K / Vegpool

Many people take high doses of vitamin B12 every day. In particular, elderly people, patients with type 2 diabetes and people living vegans are often recommended to take vitamin B12 in the form of a preparation.

The daily dose of vitamin B12 seems extremely high to many people (because according to the dietary recommendation, a few milligrams a day are enough).

Targeted overdosing is recommended because only a very small part of the vitamin ingested is actually used. The body excretes most of it unused.

Of course, for many people the question arises whether there is also a dangerous overdose of vitamin B12. Whether too much vitamin B12 could have adverse health effects.

Vitamin B12 is a water-soluble vitamin. Unlike vitamin D, for example, vitamin B12 can be relatively easily "disposed of" by the body in the urine. With a normal intake of vitamin B12 supplements there are therefore none acute Expect damage.


However, recent evidence has shown that long-term overdose of B vitamins can increase the risk of lung cancer. Although vitamin B12 does not cause cancer itself, it can promote the growth of existing precancerous stages. For this reason, the intake of B12 supplements should be controlled (blood test, e.g. every 1-2 years).

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No problem with normal dosage

Basically, the oral intake of vitamin preparations with a (often recommended) daily dose of approx. 250-500µg is considered unproblematic if the B12 blood values ​​are within the reference values.


An excessively high vitamin B12 level in the blood should be avoided just as much as a vitamin B12 deficiency.

In the case of a vitamin B12 absorption disorder (e.g. lack of intrinsic factor), the doctor usually recommends an injection.

If vitamin B12 is given as an injection (syringe) in high doses, this can lead to rashes around the puncture site in some people, which disappear again after a short time. Whether this only occurs when (synthetic) cyanocobalamin is administered is controversial.

B12: Which dosage form do you prefer?

Sure: Anyone who intends to overdose with vitamin B12 and swallow a handful of tablets a day may have to reckon with consequences. The carrier substances could also play a role here (e.g. alcohol in vitamin B12 drops).

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vegan vitamin B12 supplements

Basically: With normal vitamin B12 supplementation with commercially available, over-the-counter preparations, no dangerous, acute side effects are to be expected in healthy people (even if 1,000 µg / day is already a deliberate overdose).


Nevertheless, to be on the safe side, you should have your vitamin B12 blood level checked regularly - e.g. B. once a year. Then the daily dosage can be adjusted to the actual needs.

We revised the article on February 15, 2021 to include the latest findings on overdosing.

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Author: Kilian Thirty