Is FT4 useful for Langlebigkeit?

Whether FT4 (free thyroxine) is useful for longevity is not clearly supported by current evidence. FT4 is a key marker of thyroid function and influences metabolism. Some observational studies suggest that slightly lower thyroid activity is more common in centenarians, possibly as a protective mechanism against excessive metabolic rate. However, the evidence is weak and based on associations, not interventional trials. A single FT4 value without context (TSH, T3, age, symptoms) has limited predictive value for longevity. Moreover, seasonal variation, lab errors, or medications can affect results. In precision medicine, FT4 is useful as part of a comprehensive thyroid panel, but not as a standalone longevity biomarker. Clinical practice recommends confirming abnormal values and consulting a physician. Evidence grade: unclear (mechanistic/epidemiological).