I was just asked this question again today and I've been meaning to post about this, but then I always forget.
Doctors and pharmacists always say you need to take your thyroid medication on an empty stomach. Why? Because food, especially foods with calcium or iron in them, will interfere with thyroid hormone absorption from your stomach. Also, some medications, like antacids, can bind to the thyroid medication and prevent absorption. (Caution: If you do take other medications along with thyroid meds, check with your pharmacist to see if there might be any interactions between drugs or any reason that you absolutely need to take them separately from your thyroid meds.)
Here's the scenario: You're newly diagnosed with thyroid disease and need to start taking medication. Upon hearing that you need to take it on an empty stomach, you realize that means you won't be able to eat breakfast in the morning for an hour even if you tke the pill first thing when you wake up. That disrupts your whole morning routine. So you get this great idea: you'll wake up an hour early, take your pill, and go back to sleep. Sounds great, right?
WRONG! Not fun. Plus, how many times do you wake up out of a sound sleep and have to do something, and then can go right back into a sound sleep for another hour? (If you can, then you're either lucky, or not perimenopausal)
One of the biggest fallacies about taking thyroid meds is the waiting an hour until you eat. If you always do the same thing, and are always consistent, the absorption thing will work itself out in the testing and dosing. I take mine every morning with my coffee (which has milk in it) and I eat breakfast soon after. You need your sleep more than you need to be woken up every morning just to take a pill. I know so many people who think they have to do it that way and really, it makes no sense.
Here's what I learned from my old endocrinologist in Arizona. She had her thyroid removed and took thyroid meds every day. She took hers with her morning latte. She explained it like this:
If you always have the latte, then the test will be based on your thyroid med absorption with the latte. So whatever your TSH comes out to be based on thyroid meds with latte, you can be medicated based on thyroid meds with latte.
I never worry about it, and I've never had a problem. In races, like I said, just do it when it's the same time of day. One day doesn't make all that much difference in your overall TSH if it's done slightly differently due to a race. Especially considering you'll only be getting tested every few months at the most.
Enjoy your sleep! (And your coffee)