Inequalities in Health
Michael Marmot, Ph.D. / New England Journal of Medicine, v.345, n.2 12jul01
Michael Marmot, Ph.D., University College London, London WCIE 6BT, United Kingdom
WALK the slums of Dhaka, in Bangladesh, or Accra, in Ghana, and it is not difficult to see how the urban environment of poor countries could be responsible for bad health. Walk north from Manhattan's museum district to Harlem, or east from London's financial district to its old East End, and you will be struck by the contrast between rich and poor, existing cheek by jowl. It is less immediately obvious why there should be health differences between rich and poor areas of the same city. It is even less obvious, from casual inspection of the physical environment, why life expectancy for young black men in Harlem should be less than in Bangladesh.1
Geographic variations in health within rich countries arc substantial. White men in the 10 "healthiest" counties in the United States have a life expectancy above 76.4 years. Black men in the 10 least healthy counties have a life expectancy of 61 years in Philadelphia, 60 in Baltimore and New York, and 57.9 in the District of Columbia.2 The 20-year gap in life expectancy between whites in the healthiest counties and blacks in the least healthy is as big as differences between countries at very different stages of economic development. The best off are like Japan; the worst off hover around the level of Kazakhstan and Bangladesh.3 The low life expectancy in poor countries may be the result of starvation, infected water, and poor sanitation. The low life expectancy of people who live in poor areas within rich countries is not. The major contributors to excess deaths among men in Harlem are circulatory disease, homicide, and infection with the human immunodeficiency virus.4
Does the social environment have a role in generating differences in health between residential areas? Is health status worse in poor areas because poor people live there, or are there features of the environment that might predict ill health over and above the socioeconomic characteristics of the residents?5 In this issue of the Journal, Diez Roux and colleagues suggest that the answer to both questions is yes.6 These investigators show that individual socioeconomic characteristics, particularly income, are related to the incidence of coronary heart disease, with poorer people having a greater incidence of disease. In addition, they divided neighborhoods into groups on the basis of household income and other socioeconomic characteristics, separately for blacks and whites. Among whites, as among blacks, the worse off the neighborhood, the higher the incidence of coronary heart disease. By bringing together two levels of analysis communities and individual residents - Diez Roux et al. show that socioeconomic characteristics of communities, in addition to individual characteristics such as income, education, and occupation, are related to the incidence of coronary events.
Is poverty at the root of the associations between ill health and the socioeconomic characteristics of both individuals and neighborhoods? The relation is not that simple. There are poor countries that achieve good health at low cost. Life expectancy in China, Sri Lanka, and Kerala (a sizable state in southern India) exceeds 70 years, despite their having gross national products in 1994 of less than $1,000 per capita.7 Contrast this with Harlem, where there was a median family income in 1990 of $24,174 yet a probability of only 37 percent that a black man would survive from the age of 15 years to 65 (as compared with the U.S. average of 77 percent for white men ).4 Poor people in the United States are rich by world standards, but they have worse health than the average in some poor countries.
Poverty is more complex than simply a lack of money. According to Diez Roux et al., the most affluent group of black neighborhoods (containing approximately a third of the black study subjects) had about the same median household income as the worst-off group of white neighborhoods. The worst-off-whites had a higher incidence of coronary events than the best-off blacks. Yet for both blacks and whites, there was a social gradient in the incidence of coronary events: the worse off the neighborhood, the higher the incidence. Thus, inequalities in health are not confined to poor health among the most deprived. Studies by my colleagues and me of British civil servants, known as the Whitehall studies,8,9 demonstrated that among white-collar workers, none of whom were poor by any usual standard, mortality and morbidity followed a social gradient -with higher rates as the social hierarchy was descended. The lower the grade of employment, the higher the mortality from coronary heart disease, from all causes, and from most other major causes of death.
We have, then, to explain not only why the poorest members of rich societies have higher rates of disease, but also why health follows a social gradient. It is all too easy to assume that either advances in understanding of the molecular basis of disease or broader access to higher-quality medical care will solve the problem of disparities in health. This is unlikely. In the United States, as in Britain,10 the magnitude of the gap in health has increased - that is, the slope of the relation between education and mortality has grown steeper" and the advantage of healthy counties in terms of mortality has widened.2 Whatever hypothesized genetic factor may be conjured up to explain the plight of people in disadvantaged circumstances, it could not have changed in a few years. If research on the genome is to help us understand inequalities in health, it will have to clarify how genes interact with environmental influences.
What of differences in medical care? One oft-cited comparison is that the social gradient in mortality is similar in Britain, where there is a National Health Service, and the United States, which is without one. Universal provision of health care may still hide differences in access and utilization. The fact that there are socioeconomic differences in medical care does not mean that these are the cause of differences in morbidity and mortality.
Health might also be a determinant of social position, rather than the reverse. For this factor to account for differences between neighborhoods, it would have to be argued that sicker people migrate to poorer neighborhoods - something that is plausible, but unlikely to be the primary explanation.
The usual explanation for inequalities in health is lifestyle. There are clear socioeconomic differences in smoking and other unhealthy types of behavior that are risk factors for coronary artery disease. Yet controlling for these factors had little effect on the socioeconomic differences in coronary heart disease in the study by Diez Roux et al. The first Whitehall study of British civil servants had a similar finding.2 Something in addition to socioeconomic differences in smoking, physical activity, hypertension, diabetes, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and body-mass index must be responsible for the differences in the incidence of heart disease.
The extent to which inequalities in health are the result of material or psychosocial factors is also uncertain.12,13 We do not know the extent to which social circumstances influence disease pathways through exposure to physical, chemical, and biologic agents, or through the mind. My own view is that the mind is a crucial gateway through which social influences affect physiology to cause disease. The mind may work through effects on health-related behavior, such as smoking, eating, drinking, physical activity, or risk taking, or it may act through effects on neuroendocrine or immune mechanisms.14
There is evidence to support this view. In the Whitehall II study, for example, we examined a psychosocial characteristic of work, termed "low control" - meaning that an individual worker had little control over his or her daily activities in the workplace. We showed that it was an important predictor of the risk of cardiovascular disease and that it had an important role in accounting for the social gradient in coronary heart disease and depression.9, 15 Looking outside work, we also showed that people who reported feeling low control at home and over life circumstances in general had an increased risk of depression; this was particularly apparent among women in low-status jobs.16
Psychosocial factors might also apply to communities. Living in a disadvantaged community may be bad for health because of lack of access to amenities, which in turn may affect access to healthful foods, to opportunities for physical activity, and to medical and other services. In addition, insecurity, fear of crime, suffering from the effects of a low position in the socioeconomic hierarchy, and lack of social support are all features of disadvantaged communities that might increase inequalities in health.
Describing the social gradient in morbidity and mortality in terms of "inequality" draws attention to the fact that death and illness are related to social inequalities. Perhaps this is why a conservative government in Britain in the early 1990s abolished the term "inequalities" in health and replaced it by the blander "variations." One of the first things a Labour government did in Britain was to restore "health inequalities" to the language and to the health agenda and to ask what could be done about them.10 In the United States, the subject has become known as "health disparities." As research develops, it will become important to ask the question of how an understanding of health disparities might help correct some of the problems of deep-seated social inequalities. The findings of Diez Roux et al. suggest two potential targets of intervention: enhancing the social and psychological resources of individual people, and improving the duality of neighborhoods and communal life.
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