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Thyroid UK
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Vit B12 & Folate

Due to low B12 & folate blood results I've been taking Jarrow Methylcobalamin B12, 5000mcg along with Jarrows B-Right Optimized B-Complex. I was having night sweats before I began taking these which stopped.

Recent blood test showed a great increase in B12 (1,000+) but not much progress in folate - I have therefore stated taking Solgar 400 mcg Folate Metafolin.

At the same time (about 2 weeks ago) I reduced the B12 (I'd done 60 days @ the 5000mcg) to Solgar, Sublingual Methylcobalamin, 1000 mcg - I changed brands as the Jarrows 1000mcg was lemon flavoured & I prefer the cherry flavour.

Over the past few weeks the night sweats have began again, I'm guessing this is all down to a lowering in my B12 again.

I was thinking of increasing my daily supplement to 2 x 1000mcg to see if this helps. Am I right in assuming that I need to take the B12 supplements forever now or will my body start to produce B12 itself after a while?

6 Replies

I'm afraid any blood test done for B-12 once you are supplementing is pretty much null and void. Don't reduce your B-12 intake, if you take excess that your body doesn't need it will just flush out of your system as B-12 is water soluble. You cannot store B-12 in your body (unlike, say, Vitamin A or D) and so yes, you'll probably always need to take it, although in time you would likely lower your intake.

I'm sure someone else might know whether there's any way to measure B-12 once you are on supplements.

So glad to hear your sweats have diminished/gone! That's great. Wish mine would! :D


Thanks for that, I suspected I'd need to keep going with them.

I followed advice on here to start with the 5000mcg & reduce down after 6-8 weeks. I think I'll up my dose & see what happens.

Trying to get all me ducks in a row before I start my Thyriod S (when it eventually get here :-))

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The active B12 test will give you an accurate result even when taking B12, I believe. The normal test you usually get is a serum test. The active test tests what's in the cells, if I've understood correctly. :)


both serum B12 and active B12 test suffer from one flaw - they show you what is going on in the blood - not what is happening at the cell level.

Having supplemented further testing of B12 is unlikely to help. However, you can still be tested for PA (the most common absorption problem) with the IFA test though you will need to stop supplementing for a week. Please also note that the test gives false positives a lot of the time so a negative isn't conclusive evidence that you don't have an absorption problem.

Please look at the pinned posts on the PAS forum


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Wow this is a minefield - I think I'm beginning to understand things & then I discover something new!

Having read the symptoms of PA they are very similar to hypo & the menopause, so I'm confused. I'm convinced that I am hypo, GP thinks I'm menopausal (I'm 43)!

My last BH test results are below:

My TSH was 4.66 (027-4.2)

FT4 16.22 (12 -22)

FT3 5.4 (3.1-6.8)

B12 256 (insufficient 140-250).... increased to 1000+ at last test

Serum folate - 13.41 (10.4 -42.4)

GP has recently tested hormones which came back 'normal for pre menopause', which she read as me being menopausal! She re tested my TSH which came in around 3.6, but with a top range of around 6 ( I don't have the actual results to hand), but no FT3 or FT4. Doc says everything is in range so I'm ok!? Very disillusioned with my GP so trying to help myself.

I did start to feel better once I began supplementing with the B12 & there has been a definite change since I lowered my dose, so I'm thinking that I don't have problems with absorption - does that sound right?

I currently waiting for a delivery of Thyroid S & hoping I can start feeling human again soon.

Sorry for the long reply but its a lot to take in & everyone on here is so knowledgeable & helpful.


1% of B12 is absorbed passively outside the ileum so it is quite possible to get enough B12 orally/sublingually if you are taking high enough doses - 1000mcg is about 400xRDA so ...

I found my B12 levels significantly affected my response to peri-menopausal symptoms.

Strictly speaking the menopause is the point at which your periods stop - you are still pre-menopausal whilst you are having periods and post-menopausal means that you haven't had a period for a year.

folate isn't great and could easily have been depleted given the amounts of B12 you are taking - best from food but if you have absorption problems then you may need to supplement.


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