How are FT3 and gut health related?

The relationship between free triiodothyronine (FT3) and gut health is complex and an area of active research. FT3, the active thyroid hormone, is primarily generated by deiodination of T4 in peripheral tissues such as the liver and kidney. The gut microbiome can influence this process by modulating the availability of trace elements like selenium and zinc, which are essential for deiodinase enzymes. Additionally, gut inflammation (e.g., in celiac disease or Crohn's disease) can impair the absorption of thyroid hormones, potentially altering FT3 levels. The intestinal barrier function also plays a role: increased permeability ('leaky gut') may trigger immune responses that affect thyroid function. However, these connections are largely based on mechanistic studies and observational data; direct clinical evidence from the provided context is lacking. The effects are individually variable and not suitable as sole diagnostic criteria. Any abnormalities in thyroid function should be evaluated by a physician. Therefore, the evidence is classified as mechanistic.