14. Lifespan, Healthspan, and Longevity Are Related but Distinct Terms

Lifespan is the total time an organism is alive (a survival outcome shaped by its aging regime and environment), summarized by metrics such as mean lifespan, maximal lifespan, and survival/ hazards (28). Species lifespan is broadly defined by genetics and is influenced by environment and chance. Healthspan is the time during which function remains sufficient for typical demands and major chronic disease and disability are absent; it is quantified as disease-free survival, disability-free survival, or years with preserved function/intrinsic capacity (or related composites). Unlike lifespan, healthspan is an operational and context-dependent concept, defined relative to functional requirements, environmental conditions, and compensatory capacity rather than an intrinsic biological state. Healthspan can be improved without large changes in lifespan (e.g., by strengthening weak links in organisms or increasing tolerance to accumulated burden), but slowing the deleteriome rise or its resetting should, in principle, extend both. Exercise is an illustrative case here: some of its benefits may reflect lower damage production or improved maintenance, but many likely arise from increased reserve, stress tolerance, and recovery dynamics. Longevity is often used as a synonym for lifespan, but it is also used as the realized ability to reach late ages, a whole-organism outcome that depends not only on the rate of deleteriome accumulation but also on robustness, redundancy, and deficits that determine when accumulated burden becomes lethal. Accordingly, two organisms can accumulate damage in broadly similar ways yet show different longevity because burden couples to failure differently and lethality may occur at different absolute levels of the same burden. Global mean lifespan is now approximately 73 y, with the highest (in a country) approaching 90 y. The surprisingly small gap between today’s best-achieved mean lifespans and the maximal observed lifespan (currently 122 y) suggests that incremental gains may get harder, but it also clarifies the opportunity: healthspan can still improve substantially, whereas larger lifespan gains likely require new classes or combinations of interventions.