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the future of ageing
1 September 2006. By Tom Kirkwood
Progress or plateau?
There are realistic prospects of longer, healthier lifespans, but research remains a priority, and we must guard against potential new ageing risks.
If some of the more fanciful media reports are to be believed, humans might be living to 200, 500 or even a thousand years within the foreseeable future. The truth, however, is that everything we are learning about the science of ageing suggests that radical life extension is so far away, should it prove feasible at all, that we should rein in the wilder flights of fancy.
The hope for progress must come through the clear indications for malleability of the ageing process itself. There is plenty of evidence for this, both from the demography of recent decades and from basic science. In order to exploit this malleability we need a more detailed understanding of the complex mechanisms that underlie ageing and age-related disease and of how known environmental factors, including exercise and nutrition, modulate these mechanisms. Armed with this knowledge we will be able to design better ways to deliver increased health and vitality in our later years.
Contrary to those who like to think that ageing begins at 40, 50 or 60, we are learning that the underpinning mechanisms of ageing play out their mischief throughout the life course. The damage that will shape our health in old age has been accumulating within our cells since the earliest days of life in the womb. This means that we need to harness the fruits of research on ageing not only for today's older people but also for tomorrow's. Appreciating the life-course nature of ageing helps surmount the objection sometimes raised against research on ageing, namely, that we should set a lower priority on research for old people who have had their 'innings' already. Indeed, if we can deliver a world that gives greater health to older people, it will be our children and grandchildren who will benefit the most.
Given the complexity of ageing, a 'pill' for longer life seems an unlikely bet, but we should remain open to the fruits of research on model systems. In recent years we have learned much about how nutrient-sensing and insulin-signalling pathways affect the rate of ageing in worms, flies and mice. It would be surprising if similar processes were entirely without effects in humans, but we should beware of too readily making the jump between species. The biological response to the level of available energy is perhaps one of the most intense objects of natural selection. As the disposable soma theory has shown, it can hold the key to understanding why ageing occurs at all. Yet species differ in the ecological significance of energy fluctuation, and it may very well be that we humans are better buffered against ups and downs than are smaller animals.
Will life expectancy continue its current increase? Or will it, as many expect, either settle to some plateau or even fall, through the spreading effects of obesity and sedentary lifestyles? It is hard to answer these questions with confidence, and so we need flexibility in our plans. Without a fundamental change in our biology, indefinite increase seems unlikely and a future plateau seems the best bet. But at what level? If, however, the worst happens and life expectancy reaches a peak and then declines, research on ageing will lose none of its urgency. This is because the adverse effects of unhealthy lifestyles accelerate the build-up of damage that causes ageing itself.
Whatever the future holds for ageing, it will be a time of great scientific interest and one in which science will have much to contribute to helping us succeed in one of the really great challenges of our time.
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