It is a polite fiction in some parts of the aging research community that the goal of the scientists' work is to improve health in the old without improving longevity. Like all the best polite fictions, it survives because many people have come to actually believe this line. It arose during the period when researchers couldn't talk openly about extending human life without risking their funding and their careers: proposing improvements to health in the old was the way to raise funds when you couldn't talk about extending healthy and overall life span. Sad to say, but the research and funding community was, up until comparatively recently, in the business of discouraging research and researchers who might head in that direction - or at the very least in the business of saying nothing about the matter in public. There is surprisingly little shame evident from those who engaged in those practices back in the day, now that things are somewhat different.
If we look at aging from the high level abstraction of reliability theory, it becomes clear that it should be impossible to improve health without also extending life. Aging is an accumulation of damage, and improving health involves fixing or preventing that damage. The statistics of the way in which any machinery - our bodies included - ages and fails, and the statistics of how long that failure will take to happen, depend on the level of unrepaired damage in the system's component parts. Arguing the opposite side of that position, that is is possible to fix damage without extending life expectancy, is a steep hill to climb: you have to come up with a convincing explanation as to why a human doesn't behave like any other physical system that undergoes limited self-repair - which starts to sound suspiciously like vitalism.
Nonetheless, we still see things like this, buried in the introduction to abstracts from one of last year's conferences:
The purpose of the 2012 conference was to provide a forum for the presentation and discussion of various assays of measuring physiological performance and function and determining what assays of function could be used to asses healthspan of a mouse. Longevity is a precise endpoint (binary, the individual is either alive or it is dead), but the true goal of aging research is to increase the health of the elderly, not their longevity. That is, the goal is to enhance and extend healthspan, defined as the portion of our lives spent free of serious illnesses and disabilities.
I think it's a problem that a fair proportion of researchers in this field continue to either (a) put forward the proposition that you can improve long-term health without extending life as a matter of fact, or (b) conveniently omit any discussion of extended longevity as a possible goal or result of their work. This is to say nothing of the ethics of actually trying to avoid extending life span in a field where it is a possibility.
There are some who point to the well-known "rectangularization of the survival curve" as evidence for it being possible to extend healthy life without extending overall life span. This gradual change in historical mortality rates at every age has been achieved without deliberate attempt to extend maximum life span - but nonetheless resulted in reduced burdens of biological damage at every age, largely due to control of infectious disease. One might argue that today, even considering vaccination, the majority of effort and funding in modern medicine goes towards trying to patch over failed health after the fact rather than on forms of prevention. That is something that must change, and not just by placing great weight on ways to periodically repair the cellular and molecular damage that causes aging.
In recent years, some researchers have examined survival data and point out that of the two possible contributions to changes in the survival curves - rectangularization on the one hand and increases longevity on the other - it is increased longevity that is the more important factor. See these items from the archives, for example:
- Compression of Morbidity Versus Increasing Longevity
- Structural Causes of Increasing Life Expectancy
In low-mortality countries, life expectancy is increasing steadily. This increase can be disentangled into two separate components: the delayed incidence of death (i.e. the rectangularization of the survival curve) and the shift of maximal age at death to the right (i.e. the extension of longevity). ... The gain of years due to longevity extension exceeded the gain due to rectangularization. This predominance over rectangularization was still observed during the most recent decades.
So one can't convincingly point to rectangularization as a sign that it is possible to increase health in the old without lengthening their lives, even if this were an ethical goal to be discussing.