Mostly it will affect your overall fitness and ability to workout hard and recover each day. Guessing you had a high TSA #? Take a look at your bloodwork and see if you can find that # and let us know what it was. Normal range is low 1's to low 4's, best to be in the low 2's for consistency.

Did you get Synthroid as your supplement, what dose per day? How old are you too, lots of things to think about when you start down this road, as your own bodies production will be blocked it you take too much for what you need. And just a tiny dose difference can make a big difference in your TSA levels. Hopefully others like us will chime in with their experiences.

Monty, thanks for the reply. I'll find out about the things you asked. I'm 42. The past 3 years have been the best of my life in terms of fitness and what I've been able to do on the bike and in triathlon. I focused on biking last year and got pretty strong. If you take out gravel rides, I biked 6,000 miles and averaged over 20mph. It's not flat here and I usually pulled more than anyone on group rides. Weight was 170 and CP/FTP was around 300 all year... not too shabby for a scrub. I'm pretty sure I overdid it and didnt take enough recovery (cause I'm a dude and want to go fast all the time). Not sharing to brag, just to say I do wonder if the level of intensity might have contributed to the low thyroid? They've been testing me every few months to dial in the dosage. Since I started taking the medicine, I have gained some weight. But I've also had a calf injury and havent worked out as much. I'm super interested in hearing from you and others and learning anything I can. Thanks brother.

Thyroid plays a dominant role in metabolism. Low thyroid, poor metabolism and vice versa. Any t3/t4 medication fixes the problem right away

Keep in mind thyroid levels can vary a lot based on diet (iodine) and stress...if your an active cyclist, it could just be fatigue, unless levels are abnormally low

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Strava

i had low thyroid for a while a few years back as an after effect of having high thyroid due to thyroiditis due to a virus (yes, quite a chain of events).
from my experience at least, low is better than high - you just feel a bit tired rather than being completely wrecked - but that depends on how extreme it is either way. i found when i was low i could exercise ok but had to be aware that i would struggle for intensity and recovery.

my first bit of advise is similar to monty - get all the details from your test results and track them yourself. i found it very useful for understanding and piece of mind to graph my values so i could easily see the trend. i typically find doctors are not very good at doing anything more than telling you what they think you should do.
my laymans understanding/recollection:
TSH = thyroid stimulating hormone (what monty refers to as TSA, assume that is just different phrasing) - essentially the signal your brain is sending to say it wants more.
T4 is full thyroid hormone level
T3 is available thyroid hormone ie a subset of T4
if you have low T3/T4 then you should have high TSH, in which case your body should catch up in due course. i never took the synthetic hormone as i don't like that sort of thing messing with my body and sure enough my body sorted itself out (it did take some months though and YMMV).
if you have low T3/T4 but don't have high TSH then your body is confused and you probably will need the drugs.
if your T4 is ok but T3 is low then your body is struggling to access the hormones it has.

low thyroid is commonly a sedantary/overweight persons condition (unclear which is cause and effect) but conversely it could be a result of overtraining. in one case exercise is good, in the other good only with great caution.
as always, listen to your body and don't push it beyond what it is ready for - if you know you have a medical issue then be particularly cautious

(usual disclaimer - not an MD, YMMV, listen to your doc, question them and do your own research based on specifics of your own situation)

I have a low thyroid level and mine is due to radiation treatment from throat cancer. From HPV not smoking. I take 75mg of Levothyroxine a day. My oncologist asked about my fatigue level about a year after treatment. They tested my thyroid and the cure to cancer is not quite perfected. Low thyroid function and several saliva glands that do not work, not a bad problem since it forces me to drink a lot of water. It also took about 1 year to get the dosage correct but I now feel great. Riding as well as I ever have and soon to be 64.

It will almost certainly only do good things for cycling and most other sports where the increased metabolism etc is beneficial.
Whilst not on the WADA prohibited list last time I checked, there is plenty out there about their potential performance enhancing effects.
That is not to say you should not use them, about 1/3 of the patients I look after are on some form of thyroid supplementation. You have a legitimate reason to be on them.

I'm in the no thyroid camp due to total thyroidectomy in 2019 and take 150mg levothyroxine per day. My main issue adjusting was lack of power, and I've never really got that back although that was likely due to the other treatments I went through at the time.

As has been stated, diet plays a part. I take my thyroxine immediately upon waking, then don't eat for an hour to allow full absorption. I have also cut out caffeine and dairy as this can affect absorption (although could be consumed 4 hours after taking). I'm a bit over-zealous with this regime, but it seems to work for me.

Good to have this thread - doesn't seem to come up too much.

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My race site: https://racesandplaces.wixsite.com/racesandplaces

Did you have symptoms of hypothyroidism? Or was it just identified as part of a routine blood draw?

I was diagnosed with hypothyroidism nearly 3 years ago. For me it was nearly a year of a slow decline in energy and always feeling exhausted. Regardless of how much I trained or didn’t train (and wasn’t training much I just didn’t have energy). I also had a slow development of brain fog.

I finally made appointment with doctor and thought it would be low testosterone. But was hypothyroidism. I got on medicine and within a month I felt borderline god-like with how much better I felt.

I’ve had to adjust it up a couple of times over past three years.

I only mention my story in that if you weren’t really having the symptoms or they were minor, I don’t know how much of an improvement you may notice. On the flip side it may be where you did have the symptoms, but they just took a while to develop that you never noticed, but will notice feeling better.

Regardless, it takes several weeks for the meds to work. Don’t think on day 3 you’ll feel different.

I was diagnosed with hypothyroidism about a year ago.

I am a doctor, so I knew what tests to send when I had symptoms.
The two main symptoms I had were the inability to recover properly from training sessions- it would take me like 2-3 days to recover from an interval session. Which it never had done before.
And I could not for the life of me get my heart rate up past around 165-170 no matter what I did. (My max is around 190).

I guess on retrospect I also had gained a bit of weight, and had lowish motivation but was training a fair bit, so it was not terrible.
I sent off the usual 'tired all the time' bloods and I came back with a TSH of 45!!! (which is massive). I've since tested my antibodies, and have TPO positivity- which indicated I have a 'Hashimotos thyroiditis'.

I'm now on levothyroxine- feel so much better and I'm fitter than I've ever been!
There's definitely some light at the end of the tunnel for you, and I'm glad you were diagnosed before you had symptoms.

Wow, thanks for all the comments guys.

-The medicine I'm taking is Levothyroxine 0.075MG.

-I still need to call the doc to inquire about the levels. Will get back to you on that.


Here's more information on me:

-This is not something that I noticed. Although I dont usually notice this kind of stuff until it gets bad.

-It was on the low end at my yearly physical last year. Then, when it was even lower this year, they decided to give me medicine. I started the medicine in September and have been going back every month since for bloodwork so they could dial the dosage in. Each time they increased it a bit.

-It's interesting that some people have said that it could be caused by over training because I definitely think I over trained the past 2 years.

-I have heard that low thyroid makes you gain weight, but that wasnt the case for me... quite the opposite... I was leaner than I've been since college (6 ft, 170 lbs). But, maybe the overtraining was keeping the weight gain at bay.

-I do remember feeling the brain fog and lack of energy but just assumed it was from all the hard training.

-Here's something I cant figure out - when I started taking the medicine in Sept, I gained about 10 lbs almost immediately. I was still a the same level training. Now I have backed off training some and I'm up 20 lbs...

-Not sure if it's related, but I've struggled with dehydration the past 2-3 years.