Thyroid UK
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Worried and pregnant

I had/have a B12 deficiency which I was treating with high dose lozenges every other day and my level went from 173 too over 5 hundred. On falling pregnant I started taking mum too be vits with very low 100 percent Rda b12 so much lower than 5000mcg but I started taking the big dose once a week too keep my levels topped. I've yet too have b12 checked midwife requested my next thyroid bloods include b12 levels. So now today I read in the telegraph high b12 linked too autism and now I'm scared I've done the wrong thing without checking first. 

I've started getting ear ringing again so I can only assume my levels are dropping 

Any advice thanks 

5 Replies

I hope you don't worry too much. I've read that the recommendation nowadays is to have a B12 around 1,000. They have stated 500 is too low so you might be worrying unnecessarily.' As far as I know, B12 is excreted out in urine if we take too much.

Congratulations on your pregnancy.


Thank you 


Hi I Also was very low on b12 and I am on 1000 dose every day. I  am also pregnant and I know I must be at a dose that's right for me as I feel well with it, I agree with shaws, I was also told our bodies will only absorb what's needed and pee out the excess. Try not to worry 😊 Xxx


Agree with the others, please don't worry too much. It could be because some people with high B12 don't have high levels because they supplement - they're high because they have underlying liver disease, which is actually the thing that perhaps causes autism. If indeed it does. Without seeing the study it's hard to know whether it's a conclusion that should have been drawn or whether it's just a correlation.

If it helps, low B12 has been linked to neural tube defects. Taking folic acid has reduced the numbers of children born with these by a reasonable percentage - but some doctors believe many more could be prevented if B12 was taken as well.


There are known links between LOW b12 and autism.

I haven't seen the article in the telegraph but did find this report on the study

"Although the exact biological mechanism that may underlie the link is unclear, the researchers suspect that women with high levels of these two nutrients in their blood may metabolize these vitamins differently from other women, Raghavan said. They may have elevated levels of folate and B12 because they process these B vitamins differently, or because they took in too much of these nutrients, or both, she explained."

(bold added by me - not in the original article)

So, there is a correlation but the process that underlines the link hasn't been found and a lot more research is needed a) to double check the results and b) if they turn out to be correct, to establish exactly what the cause is and supplementation may or may not be a factor.

It sounds to me like they are suspecting a genetic problem called MTHFR. People with the relevant genes have problems turning folate from diet/folic acid into the methylated forms that are used by cells. As a result the folate tends to stay in their blood and they tend to have high folate levels. I'm not sure if the mechanism for processing B12 is affected in quite the same way but it would make sense if it was.

There are known links between MTHFR and autism so my money would be on MTHFR rather than supplementation.

There are a number of conditions that can occur in pregnancy if you are B12 deficient that could be life threatening both for your self and the baby so having the condition treated was the correct thing to do.

"She said the bottom line is that good nutrition is still important to women during pregnancy, and mothers-to-be need to get adequate amounts of these Bvitamins from taking prenatal supplements and consuming them in foods.

"It is still too early to advocate for any changes in prenatal guidelines for these two B vitamins," Raghavan said.


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