If the association between health and socioeconomic status within
societies - at least in the developed world - is not primarily the direct
effect of material standards, then some might think it resulted simply
from differential social mobility between healthy people and unhealthy
people. However, many research reports show that this is not the major
part of the picture,17-20 and social selection is entirely
unable to account for the relation between national mortality rates and
income distribution.
This pushes us - inexorably though perhaps reluctantly - towards the view
that socioeconomic differences in health within countries result
primarily from differences in people's position in the socioeconomic
hierarchy relative to others, leaving a less powerful role to the
undoubted direct effects of absolute material standards. If health
inequality had been a residual problem of absolute poverty it might
have been expected to have diminished under the impact of postwar
economic growth, and it would tend to distinguish primarily between the
poor and the rest of the population - rather than running across
society, making even the higher echelons less healthy than those above
them (see figure 1).
Need for a theory
A theory is needed which unifies the causes of the health
inequalities related to social hierarchy with the effects of income
inequality on national mortality rates. At its centre are likely to be
factors affecting how hierarchical the hierarchy is, the depths of
material insecurity and social exclusion which societies tolerate, and
the direct and indirect psychosocial effects of social
stratification.21
Picture (right): Gin Lane - desperation strengthens the link between poverty and death
One reason why greater income equality is associated with better health
seems to be that it tends to improve social cohesion and reduce the
social divisions.11 Qualitative and quantitative evidence
suggests that more egalitarian societies are more cohesive. In
their study of Italian regions, Putnam et al report a
strong correlation (0.81) between income equality and their index of
the strength of local community life.22 They say,
"Equality is an essential feature of the civic community." Kawachi
et al have shown that measures of "social trust"
provide a statistical link between income distribution and mortality in
the United States.23 Better integration into a network of
social relations is known to benefit health.24-25 This
accords with the emphasis placed on relative poverty as a form of
social exclusion, and with the evidence that racial discrimination has
direct health effects.26 However, social wellbeing is not
simply a matter of stronger social networks. Low control, insecurity,
and loss of self esteem are among the psychosocial risk factors known
to mediate between health and socioeconomic circumstances. Indeed,
integration in the economic life of society, reduced unemployment,
material security, and narrower income differences provide the material
base for a more cohesive society. Usually the effects of chronic stress
will be closely related to the many direct effects of material
deprivation, simply because material insecurity is always worrying.
However, as Hogarth's Gin Lane shows, even absolute poverty
has often killed through psychosocial and behavioural
pathways.
Pathways
In terms of the pathways involved in the transition from social to
biological processes, there is increasing interest in the physiological
effects of chronic stress. Social status differences in physiological
risk factors among several species of non-human primates have been
identified. Animals lower in the social hierarchy hypersecreted
cortisol, had higher blood pressure, had suppressed immune function,
more commonly had central obesity, and had less good ratios of high
density lipoproteins to low density lipoproteins - even when they were
fed the same diet and social status was manipulated
experimentally.27-28 Among humans, lower social status
has also been associated with lower ratios of high to low density
lipoproteins, central obesity, and higher fibrinogen
concentrations.29 In experiments in which social status
was manipulated, subordinate monkeys "received more aggression,
engaged in less affiliation, and spent more time alone than dominants
... they spent more time fearfully scanning the social
environment and displayed more behavioral depression than dominants."
30 Loss of social status resulting from being rehoused
with more dominant animals was associated with fivefold increases in
coronary artery atherosclerosis.31
Although research has shown that psychosocial factors are related to
both morbidity and mortality, differences in reporting make
international comparisons of morbidity unreliable. Nevertheless,
because patterns even of self reported morbidity are predictive of
mortality rates, we can probably assume that mortality differences
indicate differences in objectively defined
morbidity.32-33 Although no obvious patterns have emerged
from attempts to assess international differences in the extent of
inequalities in self reported morbidity when people are classified by
education or social class, across countries there is a close relation
between the extent of inequalities in income and in self reported
morbidity.34-35
Although Britain had a greater increase in inequality during the
1980s than other developed market economies,36 the
proportion of the population living in relative poverty (below half the
average income) may - for the first time in two decades - have decreased
slightly during the early 1990s. It now stands at almost one in four of
the whole population (incomes after deducting housing
costs).37 Among children the proportion is almost one in
three. Particularly worrying is the likely increase in the proportion
of children emotionally scarred by the tensions and conflicts of family
life aggravated by living in relative poverty. During 1982-92 there
were no improvements in national mortality rates among young men (aged
20-40) and smaller improvements among younger women (aged 15-24) than
at most other ages.38 Socioeconomic differences in
mortality are at their maximum at these ages, and the national trends
are likely to be partly a reflection of the increased burden of
relative deprivation. Among young men, deaths from suicide, AIDS,
violence, and cirrhosis increased. These causes suggest that the
psychosocial effects of relative deprivation are unlikely to be
confined to health. As in the international data, where death rates
from accidents, violence, and alcohol related causes seem to be
particularly closely related to wider income inequalities, the
predominance of behavioural causes may reflect changes in social
cohesion.9 13
The papers in this series are intended to illustrate some of the
processes which give rise to the relation between relative deprivation
and health. What comes out of several of them may not have been so
different had the subject been crime, drug misuse, or poor educational
performance. Important aspects of the evidence suggest that the rest of
society cannot long remain insulated from the effects of high levels of
relative deprivation.
Funding: Paul Hamlyn Foundation.
Conflict of interest: None.
References
1 Phillimore P, Beattie A, Townsend P. The widening gap.
Inequality of health in northern England, 1981-91. BMJ
1994;308:1125-8.
2 Goldblatt P. Mortality and alternative social classifications
In:Goldblatt P, ed. Longitudinal study 1971-1981: mortality and
social organisation. London: HMSO, 1990. (OPCS series LS, No
6.)
3 Davey Smith G, Shipley M J, Rose G. Magnitude and causes of
socioeconomic differentials in mortality: further evidence from the
Whitehall Study. J Epidemiol Community Health
1990;44:265-70.
4 Davey Smith G, Neaton J D, Stamler J. Socioeconomic
differentials in mortality risk among men screened for the multiple
risk factor intervention trial. 1. White men. Am J Public
Health 1996;86:486-96.
5 Davey Smith G, Wentworth D, Neaton J D, Stamler R, Stamler J.
Socioeconomic differentials in mortality risk among men screened for
the multiple risk factor intervention trial. 2. Black men. Am J
Public Health 1996;86:497-504.
6 Office of Population Censuses and Surveys. Registrar
general's supplement on occupational mortality 1979-83.
London: HMSO, 1986.
7 North F, Syme S L, Feeney A, Head J, Shipley M J, Marmot M G.
Explaining socioeconomic differences in sickness absence: the Whitehall
II study. BMJ 1993;306:361-6.
8 Hertzman C, Kelly S, Bobak M. East-West life expectancy
gap in Europe. Dortrecht: Kluwer, 1996.
9 Kaplan G A, Pamuk E, Lynch J W, Cohen R O, Balfour J L. Income
inequality and mortality in the United States: analysis of mortality
and potential pathways. BMJ 1996;312:999-1003.
10 Office of Health Economics. Compendium health
statistics. London: OHE, 1995.
11 Wilkinson R G. Unhealthy societies: the afflictions of
inequality. London: Routledge, 1996.
12 Kennedy B P, Kawachi I, Prothrow-Stith D. Income distribution
and mortality: cross sectional ecological study of the Robin Hood index
in the United States. BMJ 1996;312:1004-7. (Important
correction. BMJ 1996;312:1194.)
13 Mclsaac S J, Wilkinson RG. Income distribution and
cause-specific mortality. Eur J Public
Health (in press).
14 Wilkinson R G. Research note: German income distribution and
infant mortality. Sociology of Health and Illness
1994;16:260-2.
15 World Bank. World development report. NewYork:
Oxford University Press, 1993.
16 Wilkinson R G. The epidemiological transition: from material
scarcity to social disadvantage? Daedalus
1994;123(4):61-77.
17 Lundberg O. Childhood living conditions, health status, and
social mobility: a contribution to the health selection debate.
European Sociological Review 1991;7:149-62.
18 Blane D, Davey Smith G, Bartley M. Social selection: what does
it contribute to social class differences in health? Sociology
of Health and Illness 1993;15:1-15.
19 Fox J, Goldblatt P, Jones D. Social class mortality
differentials: artefact, selection or life circumstances? J
Epidemiol Community Health 1985;39:1-8.
20 Power C, Manor O, Fox A J, Fogelman K. Health in childhood and
social inequalities in young adults. J R Stat Soc (A)
1990;153:17-28.
21 Sennett R, Cobb J. The hidden injuries of class.
New York: Knopf, 1973.
22 Putnam R D, Leonardi R, Nanetti R Y. Making democracy work: civic
traditions in modern Italy. Princeton, NJ: Princeton University Press,
1993:102-5, 224.
23 Kawachi I, Kennedy B P, Lochner K, Prothrow-Stith D. Social
capital, income inequality and mortality. Am J Public
Health (in press).
24 House J S, Landis K R, Umberson D. Social relationships and
health. Science 1988;241:540-5.
25 Berkman L F. The role of social relations in health promotion.
Psychosom Res 1995;57:245-54.
26 Krieger N. Sidney S. Racial discrimination and blood pressure:
the CARDIA study of young black and white adults. Am J Public
Health 1996;86:1370-8.
27 Shively C A, Clarkson T B. Regional obesity and coronary artery
atherosclerosis in females: a non-human primate model. Acta
Medica Scand 1988:723(suppl):71-8.
28 Sapolsky R M. Endocrinology alfresco: psychoendocrine studies of
wild baboons. Recent Prog Hormone Res 1993;48:437-68.
29 Brunner E. The social and biological basis of cardiovascular
disease in office workers. In: Brunner E, Blane D, Wilkinson R G, eds.
Health and social organisation. London: Routledge, 1996.
30 Shively C A, Laird K L, Anton R F. The behavior and physiology of
social stress and depression in female cynomolgus monkeys. Biol
Psychiatry (in press).
31 Shively C A, Clarkson T B. Social status and coronary artery
atherosclerosis in female monkeys. Arteriosclerosis
Thrombosis 1994;14:721-6.
32 Ostlin P. Occupational history, self-reported chronic illness,
and mortality: a follow up of 25,586 Swedish men and women. J
Epidemiol Community Health 1990;44:12-6.
33 Arber S. Social class, non-employment, and chronic illness:
continuing the inequalities in health debate. BMJ 1987;
94:1069-73..
34 Kunst A K, Cavelaar A E J M, Groenhof F, Geurts J J M, Mackenbach J P,
Socioeconomic inequalities in morbidity and mortality in Europe: a
comparative study. Rotterdam: Erasmus University, 1997. (EU Working
Group on Socio-Economic Inequalities in Health.)
35 Van Doorslaer E, Wagstaff A, Bleichrodt H, Calonge S, Gerdtham
U, Gerfin M, et al. Socioeconomic inequalities in
health: some international comparisons. J Health Econ
(in press).
36 Hills J. The future of welfare. York:
Joseph Rowntree Foundation, 1994.
37 Department of Social Security. Households below average
income 1979-1993/4. London: Stationary Office, 1996.
38 Tickle L. Mortality trends in the United Kingdom, 1982-1992.
Population Trends
1996;86:21-8.
Trafford
Centre for Medical Research,
University of Sussex,
Brighton BN1
9RY
Richard G Wilkinson, senior
research
fellow
R.G.Wilkinson@sussex.ac.uk
Despite the difficulty of disentangling material from social
influences on health, it is possible to look at the relation between
income and health in population groups where income differences are,
and are not, associated with social status. Social stratification
exists within rather than between societies. Therefore, while income
differences among groups within the developed societies are associated
with social status, the differences in average per capita incomes
between developed societies are not. We may therefore compare the
association of income and health within and between societies.
Within countries there is a close relation between most measures of
health and socioeconomic circumstances. As an example, figure 1 uses
data from 300,685 white American men in the multiple risk factor
intervention trial to show the relation between mortality and the
median family income in the postcode areas in which they
lived.
As figure 2 uses data for whole countries, the contrast between
it and the strong relation shown in figure 1 cannot arise from sampling
error. A strong international relation is unlikely to be masked by
cultural factors: not only are the international comparisons confined
to OECD countries, but the picture is supported by comparisons among
the 50 states of the United States, where cultural differences are
smaller. The correlation reported between age adjusted mortality and
median incomes in the states was -0.28.