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Thyroid UK
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Stopping B12 before blood test?

Guys I'm ordering the B12 advanced profile and thyroid plus 11 from blue horizon and I want to know if I should stop taking my B12 supplements before I do the test? I also take a tablet with the b12 that is calcium and magnesium so do I need to stop taking these? The only other tablets I take are levothyroxine and paroxetine but I'm assuming these don't matter as long as I don't take the levo before I do the finger prick? Please correct me if I'm wrong. Thanks

7 Replies

I know taking B12 messes up the test. I've seen a recommendation to leave two weeks after a B12 injection.


Four months is the necessary time to stop B12 supplements - unless you're getting an active test.

Do you really need to take calcium? It's not a good thing to take. But, if you have to take it, at least take some vit Ks-MK7 with it. :)


It does include the active B12 so can I take it or leave it? I don't like the idea of going four months without it as I feel the lack of B12 increases my anxiety symptoms. I take the calcium because there is chromium and I read that either the calcium or magnesium helps that absorb into your body. Why should I not take it? I thought it was safe. Thanks


Well, you know how, if you live in a chalky area, your kettle gets covered in lime scale? Well, so do your arteries, when you take those chalky calcium supplements. They are very difficult to absorb, and you risk a heart attack and kidney stones - especially if you don't need it in the first place! You should get tested for most things before taking them.

How's your vit D? ¨Probably low, this time of year. Get that tested, and supplement accordingly. The vit D3 will increase your absorption of calcium from food. So, then, you take some vit K2-MK7 to make sure that extra calcium goes into the bones and teeth, and not the soft tissues. Taking calcium supplements is like swallowing lumps of chalk, and not safe at all. Besides, it's very unlikely, in the Western world, that you are deficient in calcium. And, it's not a good idea to take anything you don't need.

Of course you wouldn't want to stop your B12 for four months, nobody would. But, if you're having the active test for B12, you don't have to, that's for the serum test. But, as you didn't specify...

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I did actually have my calcium tested and was on the low end of normal so I didn't actually think it would be a bad thing to increase this in the short term. My vit d will be tested as part of the thyroid +11 group of tests so I won't know if that's low yet.

As for the b12 I didn't specify as this is all new to me so I'm not sure what's relevant and what's not but it's good to know I can keep taking it, i know it was also low normal by gp standards but I felt too low given I was experiencing symptoms so I'm not wanting to stop it if I don't absolutely need to. Thanks very much for your replies, very helpful 😊


If your calcium was low normal, you should increase it by eating more calcium-rich foods, not by taking supplements. It's not so much the calcium that is bad, it's the supplements themselves. :)

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If your vitamin D is low, that may account for calcium being on low side. Extremely common to be low vitamin D with Hashimoto's (high antibodies)

If/when you supplement vitamin D, calcium will rise automatically without adding extra.

The Blue Horizon plus eleven test will tell you more on vit D, folate, ferritin and B12

As you have Hashimoto's then you may find adopting 100% gluten free diet can really help reduce symptoms, and lower antibodies slowly over time too.

Selenium supplements can help improve conversion of T4 to T3 and may also lower antibodies

Links to gluten, low D and treating the root causes of Hashimoto's





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