Thyroid UK
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Hi everyone,

After reading posts here I want to get my vit levels checked, i am currently taking a decent multivitamin (allegedly 100% of needs 🤔.......) cod liver oil, glucosamine and evening primrose oil (all of which are taken at the opposite end of the day to my levo!!)

I believe I need B12, D3, folate and Ferritin, are there any others i should include and should I stop any/all supplements to get a true reading, if so how long before.

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If you want baseline readings you will have to stop supplementing B12, iron, folate and vitamin D for 4 months while red blood cells die off and renew.

If you want current readings just skip your multi-vit on the morning of your blood test.

You want a 25-OH vitamin D test. D3 is cholecalciferol which is taken if vitD level is low.


I didnt realise it took anywhere near that long to get back to base line , sounds like a current reading is the way to go and will change the D3 request, glad I asked!!!


Hi Clutter, just wanted to comment on the 4 months in the context of taking supplement that only contains around 100% of B12 RDA.

The most common cause of a B12 deficiency isn't lack of B12 in the diet - but an absorption problem. The mechanism for B12 absorption is quite delicate and if something goes wrong here then it radically affects the amount of B12 that can be absorbed in the gut meaning that rather than getting 100% of RDA out of the tablet you would only be getting a few % - so that dose would be unlikely to have any significant impact on tests for B12.

Personally I wouldn't bother with testing for B12 unless there was evidence of symptoms (just because ranges make using the test as a guide to what is going on metabolically speaking very imprecise and symptoms always need to be part of the process of evaluating a potential B12 deficiency).

I know that evaluating symptoms can be quite difficult when there is another condition such as thyroid that has overlapping symptoms but would advice that it was definitely worth doing before running tests.

Folate isn't stored by the body so definitely wouldn't require stopping the supplementation for anywhere near 4 months.

I'm afraid that I'm not really in a position to comment on vitamin D and iron - particularly the iron in relation to ferritin as ferritin isn't a direct measure of iron anyway.

Symptoms of B12 defiency can be found here


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I wasn't commenting in the context of what the multi-vit contains but in order for Phoenix to get a baseline result of B12 it would be necessary to stop supplementing for 3-4 months. It was sloppy of me to include folate, vitD and ferritin in the 4 months.

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Some Vit D info for you -



Thankyou, another little gem for my reading list later today 👍

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