Tony McMichael directs the National Centre for Epidemiology and Population Health, at the Australian National University. A medical graduate with a PhD in epidemiology, he was previously Professor of Epidemiology at the London School of Hygiene and Tropical Medicine. His research interests have spanned various environmental and social influences on health. Recently, he has had particular interest in estimating the health impacts of global environmental change, contributing to the UN’s Intergovernmental Panel on Climate Change and the international Millennium Ecosystem Assessment project. His most recent book is Human Frontiers, Environments and Disease: Past Patterns, Uncertain Futures, Cambridge University Press (2001). In 2003 he edited Climate Change and Human Health: Risks and Responses, published by the WHO and UN agencies.

Population, environment and human health: the role of epidemiological research
by Tony McMichael

Session 6: Questions/discussion

In the course of yesterday's discussion there was very little reference to issues of human wellbeing, human biology, human health. Indeed, we heard reference to the conventional triple bottom line: the social conditions, the environmental conditions, the economic conditions. I want to argue at the beginning that actually they are not the bottom line, they are means to an end, and that the end that we ought to have in mind is actual social and human experience. That is why we are concerned about issues to do with population numbers and pressures, environmental conditions, social conditions. This session will be looking briefly, then, at some of these issues around human social, biological and health experience.

Those of you who heard Phillip Toyne speak last night at dinner will recall the description of the Easter Island experience. If you have any doubts that population and environmental conditions can impinge on human biology, human health, then his account of how they ultimately resorted to cannibalism might reinforce the message, because being eaten reduces one's life expectancy.

I am arguing here that, viewed anthropocentrically, the real bottom line in the population-environment debate is our current and future wellbeing and health. Well, do epidemiologists actually see it that way?

Firstly I would say that textbook epidemiology focuses on specific, proximal, individual-level risk factors. These are the things that we have been reading around for decades, the sort of work that implicates cigarette smoking in a range of diseases, and oral conceptive usage likewise, and dietary impacts on specific disease outcomes.

Epidemiology, as the discipline that is interested in understanding the distribution and the causes of disease in populations, not surprisingly has a preference, then, for working empirically, working in the present and the recent past to try to elucidate these relationships. It prefers specific, quantifiable variables and then it makes comparisons within and between populations. By and large, the discipline has not been very oriented to trying to estimate future trajectories of risk and changes in future population health.

So I would say that in the light of the orthodox development of epidemiology over the last quarter century or so, with an increasing focus on sophisticated quantitative methods and generally a preference for rather reductionist questions – particularly, I think, buoyed up by the rise of modern molecular biology and the opportunities that that creates for often higher-powered collaborative work with laboratory and clinical researchers – the discipline really has little interest in or capacity for tackling these questions about how larger-scale processes, like demographic change and environmental change, affect human biology, human health.

Indeed, I might say on behalf of the organising committee for this conference that in putting this particular session together we were aware that there are very few epidemiologists in this country, and indeed elsewhere at the moment, who are engaged in this larger-scale domain. And I would say that, among the few who are engaged, there are actually very few who would be prepared to argue that health is unaffected, or at least largely unaffected, by environmental degradation. So in that sense we were not able to achieve an obvious counterpoint between, as it were, liberal and conservative epidemiologists on this particular question.

I have referred to wellbeing and health, and indeed quite a few aspects of wellbeing in a broader sense have been referred to, if we include notions of material prosperity, opportunity, physical security and so on. (Those we all recognise as being part of the population-environment debate.) But actual human health has figured relatively little. I suspect that reflects a couple of things.

We really have a rather misleading model, I think, of what are the primary determinants of health in our population. We tend to see it very much in terms of personal behaviours, individual choices, the actions of free-range consumers in the marketplace; increasingly we see it as something that is influenced by genetics; and of course we see it as a reflection of medical care as a commodity. We tend not to think ecologically within that broader frame and understand how, over longer periods of time, diseases rise and fall, health problems change, in response to changing social and environmental conditions. So the model that we have I think is, in that sense, a rather narrow and misleading one.

I think also many of us assume that humans are, at least to some extent, now free of the constraints of nature, that we are a special species: we have the culture, the technology, to manage beyond those constraints that apply to other species. And I think what we are having to consider in this particular conference is how we, indeed, review that perspective and try and connect up these questions about human experience, biology and health in relation to the wider ecological constraints that apply, as a function in particular of population and environment phenomena.

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This takes me back to the Easter Island example that I have already referred to, but there are plenty of historical examples where malnutrition, the outbreak of infectious and nutritional diseases, conflict situations and survival have actually been affected by population pressures and environmental decline. I have listed four reasonably well documented examples over the last 5000 years. Each of those has occurred within a localised setting, and the interesting question that arises for us today is whether, if these things have to do with aspects of carrying capacity, we might be wanting to think about that increasingly on a larger scale and, indeed, a global scale.

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This slide is just to restate what is well known, I think, or well understood, that demographic characteristics, population size and distribution, and levels of per-person consumption and energy use and waste generation do affect environment conditions and resource base. This of course can be modulated by wise technological advance and choice, but in Australia that list of environmental conditions, which starts from relatively simple, straightforward ones and moves up to more complex ones, illustrates a number of things that we know all affect human health.

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This slide is a rather complex slide, but I just wanted to list some of the major contemporary environmental changes that we face in the modern world. Some of these are indeed very large scale. I have highlighted 'Climate change', at the top left in blue – I am just going to mention that once more in a moment – but you will see that in rather healthist fashion I have put 'Human health' right at the centre here to indicate that we are concerned about all of these things because, via a number of pathways, these environmental changes are increasingly understood to have impacts on human health. This is something now that at least some people in my trade, epidemiology, are coming to grips with.

I have highlighted those two [Climate change, and Stratospheric ozone depletion] because those, more than the others, are genuine integrated global environmental changes that arise from multiple sources but impinge more or less equally upon populations around the world. The others are worldwide but tend to vary in their local intensity and manifestations.

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As examples of the sorts of things we are concerned about, then, in a topic such as climate change and its impacts on health, I have listed [on the slide] a number of the relationships that are increasingly coming under study with respect to impacts on health. So this is a frontier for modern epidemiology, and you can see it is at a scale that is rather different from that that prevails in the conventional textbook.

So, to finish: the population-environment debate in Australia and elsewhere should emphasise human experiential consequences, especially health. A prime reason for seeking sustainable social and environmental conditions is ultimately to achieve safety, health and survival. Epidemiologists will need to broaden their horizons and their research repertoire if they are to contribute. To date they have connected better with environmental issues and aspects of economic inequality, perhaps, than with demographic, social and security issues.