Thyroid UK
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Supplementing B12

Hi Folks,

As a result of a low vit B12 test in June I have just started supplementing 1000 mcg B12 sublingual methylcobalamin and am also taking a B complex.

Vit B12 452 ng/L [>140ng/L] tested 21 June

Having had flu in March and changes in my thyroxine dosage I'm guessing I've had three to four months of low B12 with associated symptoms. My questions are: how long will it take to get my B12 levels up to 1000? Will I reach a 'steady state' when my body has sufficient? Or is it a question of adjusting doses to cope with seasons/infections etc? I have never supplemented B12 before (age 49). Is supplementing B12 something I will have to do on a permanent basis from now on?

Any help very gratefully received from this fantastic, supportive community.

2 Replies


It took 8 weeks to double my B12 from 300+ to >700 on 1,200mcg daily in 2013. I continue to supplement 1000mcg several times a week with a B Complex vitamin to maintain my levels.

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Dear Clutter,

Just what I needed to know, thank you so much, you are a star.


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