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Thyroid UK
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Need some help understanding changing levels


So, I was diagnosed with Hashimotos back when I was 18 (I'm now 31). I have been very stable with thyroxine dose and levels for at least about 8 or 9 years.

A year ago I showed as being undermedicated and was raised from 150mg to 175mg levothyroxine.

I then showed as being over and since then they keep dropping the dose. I've recently been alternating daily between 125mg and 150mg. This has again come back with being overmedicated (TSH <0.05 and T4 26 point something) and my dose is dropping to 125mg (even though I feel rubbish and truely thought I was under).

I've had a lot of lifestyle changes in the past 2 years - taken up rugby and powerlifting so built a fair bit of muscle and lost around 3.5st via a calorie defecit. I'm sure this is what is prompting these changes, but I can't come up with a valid theory on how/why.

If anyone can point me in the direction of resources or have any info I would be really greatful. I am a scientist so feel free to bombard me with the technical stuff.

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You need to know and post with the ranges: TSH,FT4,FT3, ferritin,folate,D3,B12 and antibodies for advice.

Exercise of the intensity you are undertaking will reduce the effect of the levothyroxine.


Dieting and intense exercise have probably affected your conversion and put extra demands on your T3. So, although your FT4 was over-range (I imagine, but you didn't put a range!) your FT3 could be very low.


Thanks, yes it is high. I think off the top of my head it should be under 18. I do need to go back for some tests, so I will request FT3 to be added - it was not on this test but I think was on the one before so I will check those results.

Could you explain (or point me to) how exercise puts extra demands on conversion?


Everything you do uses T3 - moving, digestion, heart beating, even thinking uses T3 - that's what it's there for. It's like your electricity supply. And, the more you do, the more T3 you use.

As you are hypo, all your T3 has to come from conversion of the T4 you are taking (levo). But, conversion needs calories. Exercise also needs calories - everything needs calories, just like everything needs T3 - so, not only have you been reducing calories in your diet, you have been using what few calories you have, on exercising, thereby reducing your conversion at a time when you need T3.

As you aren't converting your T4 to T3, your level of FT4 has risen, but your FT3 will be low. And the higher the level of FT4 rises, the worse conversion becomes. It is, if you like, a three-pronged attack you're launching, there, on your FT3 levels! It sounds as if you would not willing reduce your exercise level, therefore you have to increase your calorie intake. And, if possible, reduce your dose of levo, and add in some T3. But, as you probably know, it's getting harder and harder to get T3 prescribed. But, have a word with your doctor, anyway. :)


That's fantastic, thanks for explaining that. I have actually found some research papers that back this up too so hopefully I'll be able to book in the doctors and go armed with the evidence.


Let us know how you get on. :)


GG. You explained it really well.


Thank you. :)


Medics are currently obsessed with lowering dose so that TSH is not suppressed. But TSH when on thyroud replacement is largely irrelevant. Many patients need higher dose of Levothyroxine in order to get adequate FT3 (the only active and relevant test)

Dr Toft, past president of the British Thyroid Association and leading endocrinologist, states in Pulse Magazine,

"The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l.

Most patients will feel well in that circumstance. But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

You can obtain a copy of the articles from Thyroid UK email print it and highlight question 6 to show your doctor

please email Dionne:

Prof Toft - article just published now saying T3 is likely essential for many, or they will have to have high FT4 and suppressed TSH


For full evaluation you ideally need TSH, FT4, FT3, TT4, TPO and TG antibodies, plus vitamin D, folate, ferritin and B12 tested

See if you can get full thyroid and vitamin testing from GP. Unlikely to get FT3

Private tests are available


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results



Welcome to our forum.

Great advice from greygoose re T3 as thyroid hormones drive our metabolism once released from binding proteins & carried inside cells by receptors on the cell membrane. And T3 is the all important as once inside the nucleus it binds to the genes and increases protein synthesis and increases mitochondria's ability to burn calories and thus raise BMR. It also increases the number/size of the mitochondria, which increases BMR further…… especially the muscles.

It causes fat cells to release free fatty acids into the bloodstream where they are taken up by the tissues & burnt by mitochondria to make the ATP that drives muscle contractions and this energy can then be used to support muscle contractions for exercise, and protein synthesis for growth … and less body fat … yay ! ! ..

T3 has also been shown to cause an increase in the muscle's production of myosin, which is one of the major contractile proteins in muscles, accomplished by activating genes and causing an increase in protein synthesis in the muscles.

A calorie-restricted diet may cause the body to lower its BMR to conserve energy. It seems to me that low GI carbs and protein with a little fat is the answer. Fats are really important but it is a fine balance.

Good thyroid synthesis requires healthy levels of cortisol and excessive exercise can compromise adrenal glands by using excess cortisol instead. I read somewhere that in a healthy person cortisol kicks in after about 40 minutes of intense training but in compromised adrenals it is much faster and will supply adrenaline if cortisol is in short supply. Constant elevated glucocorticoids (such as cortisol ) will encourage protein breakdown and interfere with the HPA axis and good thyroid function.

You may find understanding how thyroid hormones work useful.


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Thanks everyone, I'm sat putting a case together for my doctor. Have a phone appointment today so hopefully I'll be picking up some more blood test forms on my way home from work tonight!


So, I had a full test including TFT3 which disappointingly came out at the top end of normal (I can't remember the figures exactly but something like 5.8 where the range is 2 or 3 to 6.4). This coupled with the unreadably low TSH and high T4 do show me as being overactive and I have reluctantly lowered my dose down to 100mg.

The Dr has ordered me a full screen of blood tests including B12, vit D, full iron studies, amoungst others just to check there isn't anything else going on. She did say she suspects it could be pernicious anaemia. I'm just waiting on the results now.

Thanks for the help on T3, after reading everything I 100% thought that'd be it.


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