Vitamin B12 Overdose Symptoms and Side Effects: Is Toxicity Possible?

As a followup to my batch of articles on vitamin B12, I get asked this question quiet a lot. Vitamin B12 is a subject of controversy and most of the people are busy messing up with its deficiency symptoms, but is it actually possible to overdose on vitamin B12? Someone on ‘Yahoo! Answers’  wrote: ‘ There are no known symptoms of vitamin B12 toxicity, because it’s water soluble and you’ll urinate most of it out. ‘, Let’s check things up to see if this statement is correct.

Vitamin B12 benefits are great. It helps with the proper formation of red blood cells in our body as well as with DNA replication, tissue growth, Myelin production (a substance that keeps your nerve cells working properly), helps lowering the levels of homocysteine in your body and even speeds up your metabolism. This vitamin is ultra-important, but B12 vitamin overdose is what we’re interested in, right?

It’s true that certain vitamins can be very harmful when consumed in excessive amounts, but it’s kind of like a basic assumption in the nutritional world that you can not overdose vitamin B12 since it is water soluble and thus is urinated in excessive amounts. The ‘scary ones’ are especially fat-soluble vitamins, like A and K – which will build up in your fat if consumed in great quantities.

B12, however, is considered to be very safe with a very low toxicity potential. Take vitamin B12 injections or sub-lingual tablets, for example. They are usually given in amounts that are far greater than the recommended daily allowance - which is 2.4mcg for an adult). We’re talking about thousands of times greater.

Vitamin B12 Overdose Symptoms and Side Effects

Can Too Much Vitamin B12 Hurt You?

I did not say that overdosing vitamin B12 is not possible, just that it is very, very rare. There have been some people complaining about headaches, numbness, itchiness, tingling and even improper kidney functioning. However, I don’t find the sample pool large enough to suggest a statistically-strong correlation for these signs.

There has also been an unusual case of acute leukemia in someone who has been treated with a megadose of B12 as a part of the treatment for pernicious anemia. Be careful not to conclude anything out of it though. Any excess amount of B12 is usually flushed out from our body, and that’s the reason it’s considered to be very safe to consume in large amounts. That applies to young and elderly men, women, nasty kids, playful children, Persian-cats and unicorns.

There’s a reason that no upper limit for B12 has been set by The Food and Nutrition Board. Overdose of vitamin B12 is so rare that there is simply not enough evidence for any toxic effect. This is by no means a medical advice, but I’d feel perfectly comfortable taking ‘regular’ B12 supplements if I had to, if toxicity and potential overdose makes you worry.

Update from Aqsa and Regev: Can You Overdose On Vitamin B12 ?

Taken from our book, ‘The B12 Deficiency Survival Handbook’ -

“Is B12 toxic in high doses? I think you already know the answer to this one. If not, I’ll repeat what I’ve said a couple of times in the previous chapters –  B12 is perfectly safe in high doses, no associated toxicity whatsoever.

I have never seen any case of an over-B12′d person. Until and if that black swan comes, it is perfectly reasonable to assume high doses are safe”

Note: I’ve written a long list of vitamin B12 foods back then. You might find it useful.

Again, this is by no means a medical advice. Always consult your doctor before applying any of my information, especially in case of pregnancy and/or breastfeeding.