Professor Tom Kirkwood - expert on the science of ageing, based at the Institute for Ageing and Health at the University of Newcastle. He gave the 2001 Reith Lecture for Radio 4, and is the author of 'Time of Our Lives - Why ageing is neither inevitable nor necessary'.

How has the average age of death changed over the past century?
At the moment, life expectancy at birth in Britain is 75 years for a man and 80 years for a woman. This has increased quite steadily over the century just passed. What we've seen particularly is that during the half century from 1950 life span has increased on the average by two years a decade and I think many people expected that these increases in life expectancy would begin to slow down as we got rid of the premature causes of death and enabled people to live to the limit of their biological potential. But actually something very interesting is happening now, and what we're seeing is that death rates at older ages are continuing to fall and life expectancy is continuing to edge upwards, so at the moment there's no immediate sign of this process coming to a natural limit.

To what extent do we inherit long life?
It's very interesting now to look at what determines how long we might expect to live. Of course, part of it's down to our genes and now there have been quite a lot of studies that have looked at the genetic contribution to longevity. These show consistently that something in the region of a quarter of what determines the length of our lives is genetic. So long life does run in families, but it's not as deterministic as the inheritance of blood group or eye colour - if you have an inheritance of just a quarter, that means that three quarters are determined by other things, and this means that many important factors of the ageing process are influenced by things like lifestyle, nutrition and exercise. I think one of the great challenges is to be able to probe the ageing process and understand how the choices that we make in life can make a difference to how long we may live and what kind of shape we may be in when we come to old age.

What is the relationship between the big killer diseases and underlying ageing?
One of the most striking things about the ageing process is that as we get older we become more likely to fall prey to any of a number of diseases which might ultimately kill us - for example cancer, heart disease and Alzheimer's disease (which doesn't necessarily kill us but robs us of our identity and does actually ultimately sort of stop us functioning so that we die of something else with increased risk) - understanding the relationship between these diseases and what we might call the normal ageing process is one of the great challenges of the day.

What we know is that we don't have some in-built genetic mechanism that programs how long we will live and turns on something that kills us - what makes us age is the build up of damage within the cells and organs of our bodies as we live our lives. So we actually need to look in close cellular and molecular detail at the processes that produce ageing or produce age-related disease. What we believe is that although individual diseases might be distinct clinical entities that require a particular course of medical treatment, there's a very strong overlap between the kinds of molecular damage that leads to the overall ageing process and that leads to increased vulnerability to these particular diseases as we get older.

How close are we to a breakthrough in tackling ageing?
I think it would be very helpful for us to get rid of the idea that there is some quick fix for the ageing process and it's just going to be a matter of a few years before scientists discover some genetic switch that can be thrown, some magic substance that will all make us live to 200 years or whatever. I think the reality is that while science is going to increase our understanding of the ageing process dramatically, and allow us to make some very real improvements in quality of life at later ages, it's going to be extremely difficult to postpone this complex process that attacks us on many fronts. It is an immensely challenging and exciting area of science and the advances that we are seeing are comparable to the kind of advances that have been seen in the last 20 years in cancer research, where we've made huge strides in understanding the process. But even these strides have shown us that in fact being able to prevent or cure all kinds of cancers is going to be a much more difficult goal to attain than people used to think perhaps 30 or 40 years ago.

Is research into extending life more important than researching the quality of that life in old age?
When we think about human ageing, the real challenge that we have is to address the quality of the later years. I think very few people would thank us if we extended life but did nothing about the quality. Already we've got a lot of extra years and I think there's great ambivalence about whether this has been an entirely good thing, given that we can expect to spend significant numbers of those years affected by diseases or conditions that rob us of a lot of quality. So, for most older people the priority is not to be able to extend life but to able to address the issues that spoil quality of life in older ages. I think when we're young and have excellent health, excellent quality of life then it's lovely to think in terms of 'yes please, more of the same'. But the reality is we will all become old and if we don't focus on the quality of those later years, in effect adding life to those years rather than adding years to our lives, then we're heading up the wrong path.

What are your top tips for longevity?
Science can give us some pretty good pointers about what we should do if we want to live a long and healthy life. The first thing you should do is choose your parents well, because if you've got long lived parents that gives you a better expectation of long life - but of course that's not an option that's open to us. The other thing you should choose to do is be a woman, because we know that women live on the average about 5 or 6 years longer, but again that's not an option for half of us. But if we look at the other things that are available to us in terms of the choices that we can make in life I think the most important thing to remember is that what makes us age is the build up of damage in our bodies, so we can make choices in life that will give our bodies the best chance of coping with the damage that attacks us.

First of all, we can avoid certain kinds of damage altogether, we know for example that tobacco causes damage to our cells, we see this in the increased of heart disease, the increased risk of cancer that comes from smoking. You can also avoid sunlight that we know damages skin. But there are much more profound things that we now can build into how we try and maintain our bodies through life - nutrition is terribly important, we can avoid foods that damage us, such as fatty foods, and we can seek out foods that we know are good for us. If we think about the things that we put into our body that ultimately will become part of our cellular structure and part of the maintenance system that we have, then we can hope to achieve quite a lot.

We should also think in terms of exercise, exercise is very good for us, it's good for the cardiovascular system, it's good for the general well-being of the muscles and skeleton, but actually there's good evidence that exercise can play a part in slowing down the rates of certain kinds of damage that may contribute to ageing. There are studies that suggest that the muscles of veteran athletes show a slower build up of mutations in the cellular power units that occur with ageing. We also see that mental exercise, exercise that tests our cognitive performance - things like crossword puzzles, playing card games, learning a new language - provides a mental stimulus. Things that engage us psychologically are also beneficial, because psychological well-being is important for physical well-being too, it's a way of maintaining our stress hormones in appropriate balance, it's a way of keeping us perhaps better protected against depression, a very common problem that afflicts far too many older people. So, there's a lot that we can do. We have to take responsibility for our bodies, we only get one body in life, we might as well look after it if we want it to reach old age in good shape.

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