Affect of exercise on thyroxine level?

Have been doing the NHS C25K running plan and have got to the end of week 5, which included a 20 min run which went fine but have now got hypo symptoms.

Am a bit surprised as my Levo dose was increased a few months ago so should be right near the top of the range so wasn't expecting any probs.

Has anyone else had a similiar experience?

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8 Replies

  • One possible reason is that exercise increases cortisol levels. High cortisol inhibits the conversion from T4 to T3, and increases the amount of T4 which gets converted to reverse T3.

    Have you ever done an adrenal stress profile saliva test to find out what your cortisol levels are?

  • This link might be helpful :

  • Thanks for your thoughts humanbean.

    Would be extremely surprised if I had high cortisol as in a blood test that I had done a few months ago it was on the low side. Since then there has been a change in the dose of another replacement hormone that I am on, which would have had a beneficial affect on my cortisol level but I don't think it would have had that drastic an affect to take my cortisol to the other extreme.

  • I don't think Humanbean was meaning that there was necessarily anything wrong with your cortisol levels. Exercise reduces T3 levels (because of the production of cortisol). That's likely to leave you feeling tired.

  • There's another interesting discussion about exercising with hypoT here:

  • Thanks for the link, pretty interesting.

  • It is very likely that as your exercising you need more thyroxine as the metabolism at a cellular level has increased and this could explain your hypo symptoms

  • I agree, I'm just a bit surprised as my ft4 level is probably near the top of the range so didn't expect exercise to have that big an affect.

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