Lifespan and healthspan are not the same
Lifespan is total years lived; healthspan is the portion of those years spent free of chronic disease and disability. For most people the two diverge — a long final stretch is spent managing illness — and it is that divergence, not lifespan alone, that longevity research is most concerned with.
Framed this way, the target is compression: pushing the onset of age-related disease closer to the end of life, so that the healthy span and the total span move together.
Why more years is not the point
The value people place on later life is carried by function: the ability to move, think, recover and live independently. A longer life spent without those is not the outcome the field is aiming at, which is why interventions are judged against functional and disease outcomes rather than survival alone.
What the field actually studies
Modern longevity research is organised less around single diseases and more around the shared biological processes that drive ageing itself. The most influential organising framework — the hallmarks of ageing — sets out a small set of interlinked mechanisms that recur across tissues and species, and it is the map most of the field still uses.
It is a genuinely active and genuinely uneven field. Some interventions rest on decades of animal and mechanistic work; the human outcome evidence for many is still thin. Treating those two situations as the same is the most common error in how longevity is discussed.
