Telomeres are repetitive DNA sequences (TTAGGG) at chromosome ends, with associated protein complexes (shelterin). Prevent chromosome ends from being recognized as damage.
Mechanism — Each cell division shortens telomeres by 30-200 base pairs. Below a critical threshold, cells trigger senescence or apoptosis. Telomerase (active in germ cells, stem cells, and many cancers) can rebuild telomeres.
Use case — Telomere length is one input to biological age. Measured commercially (TeloYears, Life Length). Slowed via exercise, sleep, stress reduction, vitamin D, omega-3s. Telomerase activation (TA-65) has modest data.
Caveats — Telomere length is noisy as a single measurement. Activating telomerase aggressively has cancer-risk concerns. Treat it as one signal among many.