Rethinking Aging Reversal: Biomarkers Must Meet Functional Gains

A Cell Metabolism commentary argues that 'reversing aging' cannot be defined by a single biomarker alone; convincing reversal requires both younger molecular patterns and lasting improvements in function (grip strength, memory, mobility), plus replication across measurements. Trials like CALERIE show mixed aging-marker results (DunedinPACE slowed slightly; PhenoAge/GrimAge unchanged), underscoring the gap between biology and daily function. The authors propose practical checks (same measure before/after, persistence after the intervention, orthogonal replication) and highlight XPRIZE Healthspan as a model for assessing rejuvenation across multiple domains.