Thyroid UK
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When trying to raise levels (ferritin, b12, vitamin D) how long do you wait before retesting?

I don't actually know my vitamin D levels so I'm taking 5,000 iu daily at the moment and will ask for a test when I see my GP next (whether I'll get one is another thing!). But how long after the first test should I wait before retesting all of these?

Also, as regards to the Vitamin D3, should I be taking anything with it? Is calcium a factor?

Thank you for any advice :)

10 Replies
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Hi sip1 K2 should always be taken with Vitamin D supplements to enable the increased uptake of calcium from your food by the Vitamin D to be directed to the tissues and bones instead of the arteries.

Also - if your GP won't test your Vitamin D, City Assays in Birmingham will send a blood spot test by post for £28. You can test this at any time.

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Thank you - that's a pretty good price as the cheapest Vit D test I can find is £39.

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It's an NHS hospital too so does a lot of the testing for the NHS :)

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Sip - important cofactors needed when taking D3:

vitamindcouncil.org/about-v...

You shouldn't take D3 unless you know your Vit D level, excess Vit D is stored and can cause problems. You would be best getting it tested with City Assays first then post the results and we can suggest an appropriate dose. The results are back in 2-3 days, where your GP test (if they will do it) takes a lot longer.

Also, D3 and K2-MK7 (the correct form) are both fat soluble so should be taken with the fattiest meal of the day, D3 four hours away from thyroid meds.

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Ok thank you - I'll do that then just to be sure. I won't be seeing my GP for another week anyway so I guess I'll have it done and the results back earlier that way!

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Do you happen to know how long we should wait before retesting vitamins and iron?

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Some take longer than others to make a difference, and of course it depends on your level to start with and what dose of supplementing you take.

I retested after 2.5 months and managed to increase folate from bottom to top of range, increased Vit D from severely deficient at 15 to 200 (had to adjust dose to reduce the new level), and improved B12 from 600ish to 1000. Ferritin was a disaster for me, I couldn't tolerate iron supplements so have eventually raised mine by eating liver.

If you are taking ferrous fumarate then you should finish the packet of 84 tablets, leave it one week then retest.

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I'm trying the gentle iron first, but taking 2, 25mg. B12 I'm taking 2000 - 3000 mcg. Would 2 months be a good time to recheck these? Right now my ferritin is 37, and my B12 is 372 I think.

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Possibly not long enough, I think I'd wait 3 months. You've a long way to go with the ferritin and you're only taking 50mg elemental iron daily whereas ferrous fumerate contains 65mg in one tablet.

Retesting B12 won't give you an indication of what you're holding onto unless you stop for 4-5 months. Retesting whilst supplementing just tells you that you are supplementing, but I find it useful as it tells you if you are supplementing too much or too little. I adjust my B12 dose on the result when I do test and it seems that for me taking 1000mcg daily for 5 days a week keeps me at around 1000.

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Once you have the correct Vit D level, remember to retest every 6 months. I use City Assays too

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