What role does FT3 play in Langlebigkeit?

FT3 (free triiodothyronine) is the biologically active thyroid hormone that regulates basal metabolic rate, mitochondrial function, and cellular energy metabolism. In longevity research, a link between lower thyroid activity and extended lifespan has been discussed, primarily based on animal studies and observations in centenarians who often show slightly reduced FT3 levels. However, the evidence is mixed: chronically low FT3 (hypothyroidism) is associated with increased mortality, cardiovascular disease, and cognitive decline. The so-called 'low T3 syndrome' in chronic illness or aging is more likely an adaptive response rather than a healthy state. Direct recommendations to manipulate FT3 for longevity are not supported by clinical trials. MyBody-X tests do not routinely measure FT3; anyone wanting to assess thyroid status should use medical laboratory diagnostics. Interpretation of FT3 requires context of TSH, fT4, and individual symptoms. Caution against self-medication with thyroid hormones – it can cause thyrotoxicosis and serious health risks.