● First, inflammation suppresses the hypothalamus-pituitary-thyroid axis. One study showed a single injection of the inflammatory cytokine TNF-alpha reduced blood levels of TSH, T3 free, T4 free and TRH for 5 days. This shows inflammation disrupts the production and regulatory mechanisms of thyroid hormones.
● Second, inflammation decreases both the number and sensitivity of hormone receptors. If there aren't enough receptors, or they aren't sensitivity enough, it doesn't matter how much thyroid medication we take.
● Third, inflammation decreases the conversion of T4 to T3. T4 is the inactive form of thyroid hormone. The body must convert it into the active T3 form before it can be used at the cellular level.