What part of "social injustice is killing people" don't you understand?
I'm prompted to write this posting by several recent conversations with people who argue (to quote one example) that it is not clear how critiques of economic processes and their distributional impacts "relate to health beyond the truism that poverty is bad for health." Well, if that's the case then the highest priority for any discussion of justice and health should be the ways in which those processes generate and perpetuate poverty, shouldn't it? (Philosopher Thomas Pogge has been making this point in the context of global justice eloquently, for many years; see in particular the section of his web page listing publications on this topic.)
I am not at all convinced that the connection between poverty (however defined) and ill health is a "truism" based on the amount of time I have spent slowly and carefully explaining the point over the past several years, so here are a few elaborations. They start with the most obvious: not getting enough to eat, on an ongoing basis, is bad for health. Can we agree on that?
Well, the number of undernourished people in the world in 2006-2008 was estimated by the United Nations Food and Agriculture Organization at 850 million, roughly the same number as in 1979-1981. (This refers to insufficient caloric intake for the activities of daily living; it has nothing to do with the four basic food groups.) Although such estimates are necessarily imprecise, more recent trends have certainly not been helped by rising food prices; global food price indices are more than twice as high as over the period 1990-2000, and a recent UNICEF report identified similar price levels in 58 individual countries. FAO's most recent annual report on world food insecurity noted a range of causes, concluding: "Climate change and an increased frequency of weather shocks, increased linkages between energy and agricultural markets due to growing demand for biofuels, and increased financialization of food and agricultural commodities all suggest that price volatility is here to stay."
So much for the global picture, but not relevant to rich Canada, right? Wrong. Using 1998 survey data from the province of Québec, the University of Ottawa's Lise Dubois found that in census tracts that ranked in the top 20 percent on scores of both material and social deprivation, almost one in four families experienced food insecurity . Closer still to home, Toronto's Department of Public Health has for many years estimated the cost of eating the Nutritious Food Basket recommended by Ontario's Ministry of Health and Long-term Care for several categories of families living on the income provided by provincial income support programs, if they are also paying market rents. In 2010, as shown in the accompanying table please, it was quite simply impossible for many people. (The Association of Local Public Health Agencies has shown that the same was true throughout the province at least as of 2008, and a coalition of dietitians and nutritionists has done a similar calculation for British Columbia.) No wonder more than 400,000 Ontarians a month were turning to food banks. Subsidized or social housing is an option in theory, but in early 2011 more than 66,000 households were on a waiting list in the City of Toronto.
Apart from direct consequences like inadequate diet or giving up dental care in order to pay for food and housing, the stress of having to cope with life on an inadequate or precarious income is itself a contributor to ill health, as pointed out by Sir Michael Marmot in his unjustly neglected book The Status Syndrome. Life for a single mother who has to drop one child off at daycare and another at school as part of a two-hour one-way commute on foot and by transit to a low-wage job is far more stressful than for a comfortable suburbanite; among other things, there's not a lot of time or energy left to seek out healthy foods, or for comparison shopping to stretch the budget. (And yes, in my experience this does have to be explained to people, especially if they haven't set foot on a bus in years.) Colloquial references to stress distract us from the fact that the concept has a clear, and relatively well understood, physiological dimension and that its effects cumulate over time. Bruce McEwen, a leading researcher in the field, wrote more than a decade ago that "considerations of stress and health are becoming useful in understanding gradients of health across the full range of education and income, referred to as 'socioeconomic status' or SES. SES is as powerful a determinant of mortality as smoking, exposure to carcinogens, and many genetic risk factors".
SES is not only about incomes; factors like race and gender matter as well. (The concept of intersectionality, as used in feminist research, responds to this insight.) One of the more striking demonstrations of how social inequality gets under your skin was produced by Arline Geronimus and colleagues, who used data from the US National Health and Nutrition Examination Survey (NHANES) to design a measure of allostatic load – a key concept in the physiology of stress – for black and white adults, subdividing the sample by gender and into poor and non-poor based on household incomes. They found that allostatic load scores rose with age for all groups, but being poor, being black and being female each operated independently to increase the probability of a high score, and "in each age group the mean score for Blacks was roughly comparable to that for Whites who were 10 years older." In other words, living near the bottom of social hierarchies, and in particular near the bottom of multiple hierarchies, wears you out over time in biologically measurable ways. In another important study on stress effects, Bird and colleagues used allostatic load scores based on NHANES data to identify "significantly greater biological wear and tear" from living in census tracts where SES was lower, independent of individual characteristics. (Unfortunately, the full text of the study is not available on an open access basis.)
These are just two examples from a rich literature, which goes a long way toward explaining the persistence of socioeconomic gradients in health even when direct material deprivation (like not getting enough to eat, or exposure to toxic chemicals on the job) is not at issue. As Marmot points out, unanticipated expenditures (something as simple as having to come up with $200 to retrieve an illegally parked car that's been towed) and the prospect of plant or business closures are experienced very differently by workers and their employers, because of the material resources to which they have or don't have access. The literature also suggests that the familiar debate about whether to attribute socioeconomic gradients to material or "psychosocial" factors is for the most part a sterile one. Position in a social hierarchy is reflected in the material world (with apologies to Madonna), and the stresses associated with subaltern status most definitely have biological manifestations and consequences. Surprisingly, many students in public health, health promotion and related fields seem not to be exposed either to this body of research or to the texture of everyday life for the economically and socially marginalized. This last problem may arise from the fact that the relevant work tends to be generated in disciplines like sociology and urban anthropology, which aren't normally central to health curricula. In any event, in education as in research, we have a long way to go.
 L. Dubois, Food, Nutrition and Population Health: From Scarcity to Social Inequalities. In: J. Heymann, C. Hertzman, M. Barer and R. Evans,eds., Healthier Societies: From Analysis to Action (pp 135-172). Oxford University Press, 2006.