GETTING A LIFE:
LIMITS TO HEALTH IN THE 21ST CENTURY
Professor Christopher Dye
These notes and the lecture slides draw on many sources, some of which are quoted directly. I will provide these sources on request.
1. This sixth and final lecture in this series entitled "Life and Death in the New Millennium" brings together the essential points from the first 5 lectures. I will try to identify the major limits to health in the 21st century, in this country and other parts of the so-called developed world and by implication in the developing world. In the first part I'll take a few moments to examine what "getting a life" means. What are we trying to maximize, minimize or optimize? Getting to the substance, I'm then going to argue that most of what we have achieved in health in the now-rich world has come from controlling the physical and biological environment, that is, preventing illness by guaranteeing the food supply and by removing sources of infection. Having escaped the vagaries of environmental change, we are now up against limiting factors to do with our genetic makeup and our behaviour. While confronting the limits imposed by genes and behaviour, we may also have to work hard to preserve the gains we've already made; the penultimate part of the lecture points to some areas we risk losing control of the environment.
2. What does "getting a life" mean? What are we trying to maximize, minimize or optimize?
3. In this series of lectures much of the improvement in health has been framed in terms of life expectancy, which began to rise in the 1800s. But long life isn't everything.
4. A reminder of that fact came with the recent publication of Barbara Ehrenreich's book, "Dancing in the Streets: A History of Collective Joy" in which she argues that we stopped having (some forms of) collective fun sometime before we began to live longer and healthier lives (though participants in Berlin's Love Festival may disagree). It prompts the question: while gaining in the quantity of life, have we lost something in quality? And how should we take that into account in statistics that purport to quantify health and well-being?
5. Here is the standard picture of the top 10 causes of death in Western Europe now, dominated by cardiovascular disease (heart attack and stroke) and malignant cancers, and with neuropsychiatric disorders in a distant 3rd place.
6. But if we ignore premature death and consider only the quality of life as measured by years of disability we get a different picture. Now mental ill health becomes dominant, a measure of the quality of life in our ageing populations.
7. When death and disability are put together (as the total number of years of healthy life lost, DALYs), then cardiovascular disease, cancers, and neuropsychiatric disorders are more evenly balanced. Deaths and DALYs are the summary statistics you will often see, but there is clearly value in having measures both of the quantity and quality of life.
8. Interestingly, the relation between quantity and quality of life does not vary much across all countries. Here I've ranked all countries in the world in terms of life expectancy from birth (red, from Japan to Zimbabwe) and compared it with the estimated number of years of healthy life from birth (HALE, green). The black line is the proportion of years of life that are healthy and - according to the estimates - it is about 80-90% everywhere (black line). In these countries life is short, but not disproportionately nasty or brutish. Of course the reasons for ill health differ greatly among countries, but the personal burden of chronic parasitic disease or infection may not be so different from, say, the burden of chronic mental illness.
9. All this is still essentially about health. I want to give you just a glimpse of the thinking that goes beyond health and into well-being and even happiness. These are, for example, Ruut Veenhoven's four qualities of life, which combine inner and outer qualities with life chances (opportunities) and life results. He draws parallels between the way in which we view quality of life (blue) and similar thinking in ecology (green) and economics (red). While accepting that there are parallels, I'd also note one key distinction: health is more or less objectively measurable, whereas well-being and happiness are essentially subjective. So we have to be willing to lose some objectivity in adopting this scheme, while perhaps gaining a little more insight into what people really care about.
10. Veenhoven has developed a scoring system to evaluate how many years are lived, not just of healthy life but also happy life (HLE). HLE scores are systematically higher in nations that are most affluent, free, equal, educated, and harmonious. Together, these country-characteristics explain 70% of the statistical variation in HLE among countries. Surprisingly perhaps, HLE is not significantly related to unemployment, state welfare and income equality, nor to religious affiliations or trust in institutions. HLE does not differ either with military dominance and population pressure. Switzerland comes out top with 64 years and Zimbabwe bottom with 12. This makes a certain amount of sense (and is strongly pinned to health statistics), but I'd want to look into it a bit further. I work in Switzerland, where happiness is, shall we say, expressed somewhat subtly (see http://worlddatabaseofhappiness.eur.nl)
11. While well-being and happiness are legitimate goals, and we want to measure and understand life in those terms, I am going to stick to health measures for the rest of this lecture, on grounds of objectivity and familiarity. However, while claiming that health measures are objective, let me offer one further caveat. Medicine tries to be objective about the definition of illness, which is why we have the International Classification of Diseases, but there are external forces that may be less so. One cynical (and not necessarily incorrect view) is that drug companies, failing to make drugs for incurable conditions, have defined other non-existent illnesses for which they can supply drugs. This slide has a short list.
12. The major achievement of the rich world over the past two centuries was to gain control over the environment.
13. How have we made such enormous gains in health in the past 200 years? What were the contributions of microbiology and everything that flowed from it (left), versus environmental improvements (right, relieving the miseries that are still suffered in many parts of the poor world today).
14. How did we get from the patterns of survival that we still see among hunter-gatherers in Africa and South America, to the record-breaking life expectancies of Japanese women?
15. Expressed as survival curves, these are the very different fates of people in both kinds of society. There are two things to notice here: the spectacular increase in life span on more or less the same genetic background (i.e. I assume that African people would have responded in the same way given the same opportunities); and the fact that the potential for such an increase evolved while life span was short.
16. And here is how the change happened in England between 1840 and 2000. It looks like maximum life expectancy was more or less fixed, while survival at younger ages improved.
17. In fact survival in the oldest age groups has improved. Although it has done so more recently, it apparently still continues to improve.
18. The upshot is that in England life expectancy increased quickly up to about 1950. The increase slowed between 1950 and 1970, and then accelerated again. LE is still increasing and the gap between men and women has been narrowing since around 1970.
19. Why was there a slowdown after 1950? The possible reason is that the fall in deaths from respiratory diseases and infections flattened out during the 1950s. The faster gains in life expectancy since 1970 are at least partly due to the fall in deaths from cardiovascular disease, but they are not due to a reduction in deaths from cancer.
20. That is what happened. But how did it happen? First, there were improvements in agriculture, and some commentators, like Robert Fogel, have emphasized the role of agriculture above all other things.
21. In England, the number of famines decreased sharply from the 17thcentury onwards, and there were no famines in the 20th century. But this was not just about famine prevention; it was also about improving the general nutritional conditions of the population at large. Famines were the emergencies giving visibility to widespread and endemic malnutrition. Agricultural change and innovation had been going on for centuries, and it is crucial to remember that it was based on technological development as well as social organization.
22. The second most important set of innovations were the large-scale improvements in public health - the "sanitation revolution" - championed in the 19th century by Edwin Chadwick, John Snow and others.
23. And then came microbiology, from the late 19th century onwards, which opened the way to developing better drugs, diagnostics and vaccines.
24. These interventions, especially the first two acted, not additively, but synergistically. In breaking the "malnutrition-infection" complex, for example, less diarrhoea leads to better nutrition, which gives greater resistance against diarrhoeal diseases, and so on.
25. While stressing the importance of controlling the environment, we can also put in perspective the role of microbiology and the technology that followed from it. Here, for example, is the decline in deaths from tuberculosis in the 19th and 20th centuries. Most of the reduction in deaths happened before the advent of drug treatment in the 1940s (though there is still debate about whether the reduction prior to 1940 was due more to better nutrition or to isolation in sanatoria etc).
26. Another essential point in understanding these health gains is that high death rates were attributable to surprisingly few causes, as we see in the developing world today. In 2002, 86% of death from infections were due to 5 groups of infections. In 18th century England these would have been dominated by diarrhoeal disease and acute respiratory infections, especially in children.
27. And a point that applied in England then applies with still greater force in the developing world now. The remedies, for example, for preventing and treating diarrhoeal diseases, are cheap, simple and effective.
28. Last but not least, the improvement of public health through environmental control and the application of technology had to be organized, in a system where there was a "common consensus to invest in the future". In this study comparing infant mortality in different countries, the evidence is that greater social equality leads to better overall health. That may not be surprisingly, but there is a trick to getting the balance right. Full government control of health care and no government control of health care are equally undesirable. What is needed is something in between; individuals want a certain amount of choice and control over their lives.
29. Having developed social systems and technology to bring the environment under control, we are now more conspicuously coming up against the limits of genes and behaviour. The former is the product of long-term evolution; the latter is the origin of what I previously referred to as the burden of choice.
30. The bible is full of good advice that is hard to follow, such as "...I have set before you life and death, the blessing and the curse; therefore choose life..." (Deuteronomy 30:19). Some of the personal choices we have to make with respect to health are obvious but hard.
31. Take obesity. This is the general relationship between body mass index (BMI) and the risk of death (measured over a period of up to 25 years) among 50-year old men. The risk of death, in Americans in 1900 and Norwegians now, is a minimum at BMI 23-25. We can think of this picture as representing an historical transition from left to right. The risk of death for the majority fell as nutrition improved, but there is a growing proportion of people who are overweight and who are now moving up the slope on the right hand side.
32. We know about some of the behavioural changes we can make to prevent or reduce obesity: increase physical activity, eat fewer sweets, make sure children have the right diet, and so on. But some of the recommendations are more easily stated than acted upon. High energy food is easily affordable, readily available, and very irresistible. The choice is ours.
33. But the problem of obesity is not attributable entirely to a lack of self control. The determinants of obesity are more complex, and more evidence of these determinants is emerging by the week. This study, just published in Science, has identified variation in a gene called FTO that is strongly associated with being overweight or obese, and with the risk of diabetes. For example, for people with one copy of the genetic variant, the odds of being obese were 1/3 greater than for people without the gene. For people with 2 copies of the gene, the odds of being obese were 2/3 greater, and the 16% of adults with 2 copies were 3kg heavier on average. So obesity is not simply an eating problem; rather, eating habits interact with our genetic makeup to determine who will become obese.
34. In some quarters there is great optimism that such genetic constraints on health and life expectancy can be solved by technology, and can be solved quickly. One of the frontline observations supporting this view is the growth in computing power, which follows Moore's Law. The observation made in 1965 by Gordon Moore, co-founder of Intel, was that the number of transistors per square inch on integrated circuits had doubled every year since the integrated circuit was invented. Moore predicted that this trend would continue for the foreseeable future. In subsequent years, the pace slowed down a bit, but data density has doubled approximately every 24 months. Most experts expect the law to hold for at least another two decades. Moore's Law means decreasing costs: as silicon-based components and platform ingredients gain in performance, they become exponentially cheaper to produce, and therefore more plentiful, more powerful, and with the potential to help solve all sorts of technological problems, including those in medicine and biology.
35. When we put that picture alongside this one - showing the linear increase in life expectancy over 150 years - we may ask why the trend should not continue.
36. The upwards trend will continue, but will it get us to immortality? The trends in growing life span are now running roughly in parallel in the UK, USA, Sweden and Japan, after the recent Japanese catch up. Projecting these data forward, we can expect life expectancy to reach 100 in the UK around year 2100.
37. Longer life spans are of course harder to imagine, because reaching huge ages will require more radical solutions to the problem of aging. Here is one reason to think that reaching age 1000 is unlikely, at least for humans in their present form. Compare humans with other animals. Among mammals, there is a general rule which says that lifespan increases approximately with the ¼ power of body mass. This rule holds for all mammals from tiny rodents to large whales. Very crudely it suggests that a mammal that lives for 1000 years would have a body mass of the order of 10 million kg!
38. Why? A least part of the reason is that there are mechanical and physiological constraints, for example, in the mechanics of pumping blood around mammalian bodies. We know that, in mammals, heart beat decreases with the ¼ power of body mass. This puts a lower limit on mammal size at around 1g - hearts can't pump at more than about 1000 beats/minute. Notice too that, because lifespan and heart beat increase and decrease (respectively) with the ¼ power of body weight (and therefore cancel) any mammal should have about 1.5 billion heart beats in a lifetime, whatever its size.
39. So when will the increase the life span stop? Nobody knows. On the one hand, it might become costly and technically hard to fix all the faults that arise with aging. On the other hand, we may find ways to solve the really fundamental constraints on life span e.g. those to do with preserving circulatory systems, or preventing cancer.
40. Some observations indicate that it would be folly to predict where, between 100 and 1000, life span will peak. This picture alone should warn anyone off making firm predictions about longevity.
41. While we're working on extending life span, what chance is there that we will lose some of the gains we've already made?
42. Will it be back to the future? Marty McFly accidentally travels into the past and jeopardizes his own future existence. Health could get worse, not better. Is this as good as it gets? Watch out for mental illness. Melvin Udall (Jack Nicholson) has an anxiety disorder that forces him to live in a world that has shrunk to the size of his apartment.
43. Many of the serious threats arise from growing population. Malthus (18th century) was proved wrong in the short-term (or at least not exactly correct) about population outrunning the food supply, as have some of his later followers. They were wrong because of technological development and its organized application. But there must be a limit to human population size: planet earth does have a carrying capacity.
44. I've shown you in a previous lecture this vivid illustration of expanding population size - the global distribution of teenage mothers, with massive bulges in Asia and Africa where countries are yet to control fertility.
45. We don't know for sure where population will stabilize. The UN forecasts, as a median or "best" estimate, 10 billion by 2150. Many would like to see many fewer people by then (lower projection), but the worst fear is 25 billion by 2150 (upper projection).
46. The growing population will have various adverse consequences for health, some more serious than others. The threat of a bird flu pandemic is still in the news, and there are numerous other emerging pathogens that could spread around a well-connected world.
47. The next flu pandemic could be temporarily frightening, but it is not likely to reverse long-term trends in life expectancy. The most devastating kinds of infections would have these characteristics: unavoidable transmission route, be highly infectious, have a high proportion of people exposed, with transmission rapid compared with response time (everyone gets infected before knowing), and be fatal.
48. All these characteristics have applied to HIV/AIDS for most of the 25 years of the pandemic, depending on whether you think that risky sexual behaviour is unavoidable. Assuming that people know how HIV is transmitted, and given that HIV infection is 100% preventable, the onus is on individual behaviour.
49. Other such infections may emerge, but I worry more about the magnitude of the effects of climate and other environmental change. The fact that these effects will apply for decades could mean that we have time to adapt, or it could mean that the devastation will be immense.
50. This is one of the latest reports on climate change, which concludes that we must "...limit temperature increases from global warming to 2-2.5°C above the 1750 pre-industrial level..."
51. ...so as to avoid the most damaging effects of ice-melt, sea-level rise, flooding, falling water tables, drought, fires, the loss of wildlife, and so on.
52. It seems highly likely that the droughts will create political flashpoints too. It is easy to imagine many people starving as crops fail on eroded land, and conflicts over water between countries situated upstream and downstream on depleted rivers.
53. To get a sense of the consequence of social collapse, look at the disintegration of the Soviet Union after 1990. The survival of Russian men and women from age 45 to 70 during the 1990s was (and still is) appallingly low compared with their Swedish counterparts.
54. In summary...
55. When it comes to making personal choices and adjusting our behaviour, here is some advice from New Scientist on how to get a life.
56. But I'm more interested in how we developed a system for developing and applying technology that can offer this choice to individuals. As David Landes remarked in The Wealth and Poverty of Nations: "We suffer from the asymmetry between our knowledge of nature and our knowledge of man, between outside awareness and self-ignorance." This is consistent with the view that I've offered here: having come so far in controlling the external environment, we're now up against genes and behaviour.
57. In conclusion: the main achievement of C18-C20 was to control environment (food, infections); the challenge of C21 is to control genes and behaviour, while maintaining control over the environment. Many who live in the developing world are still at the mercy of the environment, though with cheap technological solutions to malnutrition and infection, plus external financial aid, they should not be. Almost any group of knowledgeable commentators would agree that "getting a life" for the majority requires "a common consensus to invest in the future", or must "...balance individual and market freedoms with appropriate public leadership..." These have been areas of failure in a number of poor countries. They are worth identifying as such, in part because they may become so again in the rich world. But it is of course far easier to make general prescriptions than to implement specific remedies.
©Professor Christopher Dye, Gresham College, 26 April 2007