I’d like to do a deep dive in how endurance training, and especially long term endurance training affects thyroid function and thyroid health, but right now I am just learning as a I go along, so I will start with a very shallow dive and hopefully as I learn more I can share more information.

For context – I have Hashimoto’s (which is an autoimmune disease where you develop antibodies which attack the thyroid) and I have recently had my whole thyroid removed in 2 surgeries.  I have had mild hypothyroidism symptoms for decades that I was unaware of until March, 2018.  I have also been a distance runner, running lots of half marathons in 2003-2010, and 3 marathons in 2012 and 2013.  I still do a lot of endurance running even without any scheduled races.  To put my endurance running in perspective, I have somehow managed to run 6 half marathons, “for fun”, by myself, in the past four months following 2 surgeries where I wasn’t allowed to run at all for 2 weeks after each surgery and had to take it easy for a week or so after I was allowed to start running again.  (It’d probably be even more than that, but I had a terrible stomach bug at 2.5 weeks after the second surgery).

When I was in the process of diagnosing my thyroid problem, I came across some articles suggesting endurance training can disrupt proper thyroid function, and at the time, I cut way back on my running because I didn’t want to do any further damage to my thyroid.  This was before my Hashimoto’s diagnosis, and I currently don’t know if my endurance running further exacerbated and already present thyroid problem, or if my multinodular goiter was going to happen regardless of what I did or didn’t do. 

One of the first articles I ran across was this 2013 blog post on the Runner’s World website by Alex Hutchinson.   The article discusses recent news about elite runners including Galen Rupp and Paula Radcliffe being diagnosed with thyroid problems, and how many of Alberto Salazar’s athletes have been diagnosed with “subclinical hypothyroidism” and have been given thyroid medication which may somehow enhance their performance.  The article also goes through several scientific publications that examine the effect endurance training has on thyroid hormone levels, the evidence thus far is a bit murky.

I have two main conclusions that I draw from this blog post:

1.) Elite athletes, especially distance runners, seem to have a lot of thyroid problems.

2.) The scientific papers addressing this that Hutchinson summarizes do not seem to cover what happens to people who are long term endurance athletes, just people who do endurance training over a short period of time like 90 days.

My thoughts on this blog:

I’m not sure how the data presented in those papers relates to me, someone who has run 100s of miles a month for 7-8 years now.  Every single time I have brought the idea of endurance running affecting my thyroid in my doctor’s appointments, my ENT and now my endocrinologist both say endurance running should not affect my thyroid function.

That being said, my endocrinologist just raised my thyroid hormone dosage yesterday because I’m not absorbing it like I should.  I mentioned my endurance running and he said that shouldn’t affect it, but I’m still wondering if this is playing a role… hopefully we can get my thyroid hormone to the right level!

As for the elite runners, I’m not sure if endurance athletes are more likely to have a thyroid problem, or if the real story is that lots of people have thyroid problems, but elite athletes are more likely to discover their problem because they are paying very close attention to their heart rate and metabolism and notice slight changes that the general public might overlook. 

The blog suggests these athletes have “subclinical hypothyroidism”, and I know for me, I definitely had symptoms when my TSH was in the “normal” zone (at 3.44).  I had a myriad of hypo symptoms when I was first diagnosed, many of those had been going on for years, and it was horrible when both my PCP and ENT both said that I was fine and that they wouldn’t treat me until my TSH was not normal (but surprise I had Hashi’s and also a thyroid that had to come out because of some suspicious nodules and now I finally have a chance to get to an actually normal thyroid hormone level artificially).

Action:  Hmm… so far I haven’t seen anything here that says I should cut back on my running.  I am trying harder to make sure I do an actual recovery day after a long run (so if I do go running, I take it easy, and maybe I take the following day off sometimes).

This Runner’s World blog post was from 2013, so I’m going to keep looking and see if I can find more information on this topic.