Myths vs facts: FT3 and longevity

FT3 (free triiodothyronine) is the active thyroid hormone. A common myth is that higher FT3 boosts metabolism and thus extends lifespan. In reality, epidemiological data show that very low FT3 in the elderly is linked to increased mortality (low T3 syndrome in chronic illness). Conversely, longevity research suggests that a mild reduction in thyroid function (low-normal FT3) might slow aging, similar to caloric restriction. However, evidence is mostly mechanistic and from animal studies; robust human trials are lacking. No direct causal link between FT3 and lifespan has been proven. MyBody-X tests measure FT3 in blood, but using it for longevity advice is speculative. Bottom line: No established facts, beware of overblown claims. Consult an endocrinologist for thyroid concerns.