Vit D3 and thyroid blood tests: Hello all, my new... - Thyroid UK

Thyroid UK

118,684 members137,673 posts

Vit D3 and thyroid blood tests

22christiana profile image

Hello all, my new GP reduced my thyroxine dose from 200 mgm to 150 after a blood test which he said showed my levels were too high. The only difference been that test and my previous ones (I've been taking thyroxine for 22 years) was that I'd started taking D3 every day a couple of months before. In others experience, does D3 make such a difference & is that why I feel so much better in the summer? Thanks!

5 Replies
SeasideSusie profile image


What were the results that prompted the reduction of your dose of Levo? Can you post them, along with their reference ranges, so that we can comment. If you don't have them, ask at your surgery's reception desk for a print out (don't accept verbal or hand written results, mistakes can be made). Dose changes should only be made 25mcg at a time, 50mcg is way to much and could make big difference to how you feel and your results.

What was your Vit D level (result plus unit of measurement) and how much D3 are you taking? Are you taking D3's important cofactors magnesium and Vit K2-mk7?

Wow, thanks for such a quick response. I'm ringing my Dr for printouts asap. I'm having yet another blood test next week (3rd now) as I see a different GP each time I go with symptoms and that's their first response. The D3 is in 2000 IU capsules but nothing else. Can I get back to you with results as soon as I get them?

SeasideSusie profile image
SeasideSusieAdministrator in reply to 22christiana

Yes, post your results when you have them.

There should be 6-8 weeks between dose change and new blood test. Also, when booking thyroid tests, always book the very first appointment of the morning and fast overnight (water allowed), this means have your evening meal/supper the night before then delay breakfast until after the blood draw, drink only water, no coffee, tea, etc, before the test.

This gives the highest possible TSH which is needed when looking for an increase in dose or to avoid a reduction. TSH is highest early morning and lowers throughout the day. It can also lower after eating and coffee also affects TSH. Also, take your Levo after the blood draw because if you take it before then your FT4 will reflect this and show higher than what is normally circulating. We usually advise 24 hours between last dose of Levo and blood draw so if you take your Levo in the morning then delay until after the test, or if you take it at night then delay that dose until after the test. These are patient to patient tips which we don't discuss with doctors or phlebotomists.

So this is my last blood test which was done in August....

Serum TSH level ...0.96miu/L

Serum free T4 level.... 16.5pmol/L

I think I've got a bit lax with taking notice of blood tests as my old GP ( now retired) used to listen to how I felt rather than rely on the results. Thank you too for the info regarding having the bloods taken.

So sorry, but just realised you asked for the results which resulted in the reduction. I'll get them sorted asap too. Also, used to always have annual blood test in February (pre vit D3) & now taken in summer which is when I feel most well. Could there be a correlation?

Thanks again

SeasideSusie profile image
SeasideSusieAdministrator in reply to 22christiana

And the reference ranges?

And Vit D?

You may also like...