Evidence check: FT3 in the context of Langlebigkeit

The provided context sources contain no information on FT3 (free triiodothyronine) in relation to longevity. FT3 is a thyroid hormone that regulates metabolism, and human observational studies suggest that low FT3 levels may be associated with increased mortality in older adults (e.g., euthyroid sick syndrome). However, the evidence is complex: low FT3 can indicate poor health prognosis, but slightly reduced FT3 in aging is also discussed as a possible adaptive mechanism. Without direct studies from the given context, any assessment remains speculative. A single FT3 value has limited predictive power for longevity and must be interpreted alongside TSH, fT4, age, and comorbidities. Evidence level: unclear.