How much vitamin B12 is safe while pregnant?

Q. Does taking high doses of vitamin B12 during pregnancy cause autism?

Answered by
Dr. J N Naidu
and medically reviewed by iCliniq medical review team.
This is a premium question & answer published on Feb 14, 2021

Hi doctor,

I am a 34 years old female, and I am ten weeks, four days pregnant. I am a vegetarian, and before I was pregnant, I would intermittently take a vitamin B12 supplement. I found the bottle two weeks ago, and without thinking about it, I started taking it daily in addition to my prenatal vitamin (which contains 4.2 mcg). Well, I finally looked at the bottle today and realized that the concentration is 1200 mcg per tablet. I read this study correlating increased risk of autism with excessive B12 blood levels, and I am very worried. I know that officially there is no upper limit and that it is water-soluble, but I do not know if there is any new information or data or clinical experience. Do pregnant women commonly take high doses for certain conditions? I was getting so worried that I was thinking about abortion. I would appreciate your honest opinion and not just reassurance.

Thanks so much for your time.



Welcome to

Oral absorption of vitamin B12 is a complex process and all the vitamins taken orally are not completely absorbed. You mentioned that you took the tablet intermittently and did not mention the exact frequency. Most studies are on patients taking high doses of vitamin B12 by injection. And still, if you are anxious, you can get your serum B12 estimated. It which will clear your anxiety.

Hi doctor,

I took 1200 mcg once daily for two weeks, and then I stopped after realizing that it was a high dose. This was during eight to ten weeks of pregnancy. I am wondering if this could have affected brain development. I am not sure if I can get my B12 level tested in my country, but I will try if you think it would be worthwhile. I would appreciate your honest opinion, but I guess there is not much I can do about it now.

Thanks again for your time.



Welcome back to

My honest opinion is that your fears are unfounded as you took B12 orally, that too for a concise duration. As I explained earlier, only a part of the orally administered vitamin B12 is absorbed into the circulation. I suggested serum B12 estimation just to reassure you scientifically. After knowing that you took the oral B12 tablets for two weeks, there is no need for serum B12 estimation. I think folic acid and vitamin B12 supplements are essential during pregnancy, especially for pure vegetarians. You did the right thing. You should be happy about it.

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