Healthspan is the period of life spent in good health, free from chronic disease and severe functional decline. Distinct from lifespan, which measures total years.
Mechanism: Determined by the rate of biological aging. Sarcopenia, cognitive decline, metabolic deterioration, cardiovascular disease accumulation. The gap between healthspan and lifespan in the US is currently 10-15 years.
Use case: The right objective for any longevity protocol. Maximize the years of strength, cognition, mobility, and independence. Don't compress the last decade into suffering.
Caveats: Healthspan is harder to measure than lifespan. Function tests (grip, gait speed, VO2 max, cognitive batteries) are the proxies.