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My doctor put me on levothyroxine 75 mcg back in January. At the time I went in my TSH was 5.7, I was anemic with a HCT of 37.5%, and my testosterone levels were 306 ng/dl Total with 6.1 ng/dl free.
I am an avid runner / cyclist that strength trains regularly so my body fat percentage is never high (5 to 9%) and I eat a whole foods diet that is rich in fruits, vegetables and lean meats / cold water fish.
My doctor had me back in to check my levels last week. In 5 weeks my TSH had dropped to 3.9, I am no longer anemic with an HCT of 41.4%. I am still awaiting my latest testosterone numbers but given how much better I feel I would suspect they have improved as well.
A noticeable metric in my performance since starting levothyroxine has been my average heart rate and peak heart rate when training. Previously on a hard core ride on the trainer (it was winter so more rides were on the trainer than outside), my heart rate would spike as high as 185 to 190. With the same level of effort, my heart rate now spikes to 170 or so. On hard runs my average heart rate would be over 150 while at a faster pace than before its averaging in the low 140s. My recovery rates have improved a lot as well and I am seeing a difference in the weight room.
So anyway let your doctor put you on synthyroid and see what your results are in a month or two. You might find it makes a big difference.