Couch to 5K
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Is an under active thyroid affected by increased exercise/fitness or is my tiredness 'normal'?

I was diagnosed with an under active thyroid last year, and put on a low dose of T4 replacement.

Bit of a random one I know but I'm just about to start week 8(!!!) and noticed that since I've got to the non-stop runs, I'm generally feeling quite tired.

I was wondering if my increased excercise and/or fitness levels may have upset my levels or is this normal for this stage of the programme, or just a complete coincidence and I need to get more sleep?!

4 Replies

In the later stages I did struggle with a lack of energy but it eventually tapered off. It may be worth checking with your GP though as changes in lifestyle can change any drug requirements.

Another thing to bear in mind after graduation is to give your body a break every 4-6 weeks to avoid tiring yourself out. Just do a week of smaller distance runs to recharge the batteries.


Hi Cattykit. I am on medication for an underactive thyroid (since 1999) and have not found that the non-stop runs have made me more tired. On the contrary, I think that generally I am feeling much more 'alive'.

It may be worth getting another blood check, your medications may need adjusting.


I am also hypothyroid and on week 6 and had the same thoughts. I agree with Markee- my general energy levels are great. The tiredness for me is just from getting up early to run and not sleeping enough! I did think my hair was looking thin but its probably just from sweat. I can't see any other of tne symptoms I had before i was diagnosed so I dont think increased exercise affects the thyroid levels.


Thanks guys, I am due another blood test soon so will bring it forward a few weeks.

Up until a few weeks ago I felt more energised so it probably is just coincidence... Or the change in the weather! :)


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