Why Is Your T4 Not Converting to T3?

Added: 2026-06-03

[00:00:00]If you have very low TSH, and you're taking thyroid hormone, then we're going to assume that the thyroid hormone is suppressing the TSH cuz you're taking hormone and your pituitary gland is picking up the extra hormone and suppressing the pituitary, so it's not making so much TSH cuz trying to reach its own homeostasis. Yet, you have low T3. So, yes, there's a conversion problem. So, how do you address a conversion problem? Well, you can address nutritionally. The enzyme that helps with conversion is 5' deiodinase.

[00:00:26]That enzyme converts T4 to T3. It's a selenium-based enzyme. It doesn't mean selenium's the only thing that's needed, but it's an important cofactor for that enzyme to function, and it's an easy target. It's an easy thing to supplement with. So, you can take selenium, which not only help to support the function of 5' deiodinase to convert T4 to T3, but also selenium is an antioxidant in its own right, so has some protection for people with Hashimoto's, which with autoimmune disease, not only do you get inflammation, you also get more oxidative stress.