Scientific American  [Printer-friendly version]
December 15, 2005


New studies suggest that the stress of being poor has a staggeringly
harmful influence on health

By Robert Sapolsky

Rudolph Virchow, the 19th-century German neuroscientist, physician and
political activist, came of age with two dramatic events a typhoid
out-break in 1847 and the failed revolutions of 1848. Out of those
experiences came two insights for him: first, that the spread of
disease has much to do with appalling living conditions, and second,
that those in power have enormous means to subjugate the power-less.
As Virchow summarized in his famous epigram, "Physicians are the
natural attorneys of the poor."

Physicians (and biomedical scientists) are advocates of the
underprivileged because poverty and poor health tend to go hand in
hand. Poverty means bad or insufficient food, un- healthy living
conditions and endless other factors that lead to illness. Yet it is
not merely that poor people tend to be unhealthy while everyone else
is well. When you examine socio-economic status (SES), a composite
measure that includes income, occupation, education and housing
conditions, it be- comes clear that, starting with the wealthiest
stratum of society, every step downward in SES correlates with poorer


Sidebar: Overview: Status and Health
Researchers have long known that people with low
socioeconomic status (SES) have dramatically higher
disease risks and shorter life spans than do people in the
wealthier strata of society. The conventional
explanations that the poor have less access to health
care and a greater incidence of harmful lifestyles such as
smoking and obesity cannot account for the huge
discrepancy in health outcomes.

** New studies indicate that the psychosocial stresses
associated with poverty may increase the risks of many
illnesses. The chronic stress induced by living in a poor,
violent neighborhood, for example, could increase one's
susceptibility to cardiovascular disease, depression and

** Other studies have shown a correlation between
income inequality and poor health in the U.S. Some
researchers believe that the poor feel poorer, and hence
suffer greater stress, in communities with wide gaps
between the highest and lowest incomes.


This "SES gradient" has been documented throughout Westernized
societies for problems that include respiratory and cardiovascular
diseases, ulcers, rheumatoid disorders, psychiatric diseases and a
number of cancers. It is not a subtle statistical phenomenon. When you
compare the highest versus the lowest rungs of the SES ladder, the
risk of some diseases varies 10-fold. Some countries exhibit a five-
to 10- year difference in life expectancy across the SES spectrum. Of
the Western na- tions, the U.S. has the steepest gradient; for
example, one study showed that the poorest white males in America die
about a decade earlier than the richest.

So what causes this correlation between SES and health? Lower SES may
give rise to poorer health, but conversely, poorer health could also
give rise to lower SES. After all, chronic illness can compromise
one's education and work productivity, in addition to generating
enormous expenses.

Nevertheless, the bulk of the facts suggests that the arrow goes from
economic status to health that SES at some point in life predicts
health measures later on. Among the many demonstrations of this point
is a remarkable study of elderly American nuns. All had taken their
vows as young adults and had spent many years thereafter sharing diet,
health care and housing, thereby controlling for those lifestyle
factors. Yet in their old age, patterns of disease, incidence of
dementia and longevity were still significantly predicted by their SES
status from when they became nuns, at least half a century before.

Inadequate Explanations

So, to use a marvelous phrase common to this field, how does SES get
"under the skin" and influence health? The answers that seem most
obvious, it turns out, do not hold much water. One such explanation,
for instance, posits that for the poor, health care may be less easily
accessible and of lower quality. This possibility is plausible when
one considers that for many of the poor in America, the family
physician does not exist, and medical care consists solely of trips to
the emergency room.

But that explanation soon falls by the wayside, for reasons made
clearest in the famed Whitehall studies by Michael G. Marmot of
University College London over the past three decades. Marmot and his
colleagues have documented an array of dramatic SES gradients in a
conveniently stratified population, namely, the members of the British
civil service (ranging from blue-collar workers to high-powered
executives). Office messengers and porters, for example, have far
higher mortality rates from chronic heart disease than administrators
and professionals do [see top illustration at right]. Lack of access
to medical attention cannot explain the phenomenon, because the U.K.,
unlike the U.S., has universal health care. Similar SES gradients also
occur in other countries with socialized medicine, including the
health care Edens of Scandinavia, and the differences remain
significant even after researchers factor in how much the subjects
actually use the medical services.

Another telling finding is that SES gradients exist for diseases for
which health care access is irrelevant. No amount of medical checkups,
blood tests and scans will change the likelihood of someone getting
type 1 (juvenile-onset) diabetes or rheumatoid arthritis, yet both
conditions are more common among the poor.

The next "obvious" explanation centers on unhealthy life- styles. As
you descend the SES ladder in Westernized societies, people are more
likely to smoke, to drink excessively, to be obese, and to live in a
violent or polluted or densely populated neighborhood. Poor people are
also less likely to have access to clean water, healthy food and
health clubs, not to mention adequate heat in the winter and air-
conditioning in the summer. Thus, it seems self-evident that lower SES
gets under the skin by increasing risks and decreasing protective
factors. As mordantly stated by Robert G. Evans of the University of
British Columbia, "Drinking sewage is probably unwise, even for Bill

What is surprising, though, is how little of the SES gradient these
risk and protective factors explain. In the Whitehall studies,
controlling for factors such as smoking and level of exercise
accounted for only about a third of the gradient. This same point is
made by studies comparing health and wealth among, rather than within,
nations. It is reasonable to assume that the wealthier a country, the
more financial resources its citizens have to buy protection and avoid
risk. If so, health should improve incrementally as one moves up the
wealth gradient among nations, as well as among the citizens within
individual nations. But it does not. Instead, among the wealthiest
quarter of countries on earth, there is no relation between a
country's wealth and the health of its people.

Thus, health care access, health care utilization, and exposure to
risk and protective factors explain the SES/health gradient far less
well than one might have guessed. One must therefore consider whether
most of the gradient arises from a different set of considerations:
the psychosocial consequences of SES.


Sidebar: Chronic Stress

CHRONIC STRESS may explain how poverty "gets under the skin" and
exerts a harmful influence on health. The risk of stress-sensitive
diseases increases if individuals lack social support, have no outlets
for their frustration and feel that their circumstances are worsening
exactly the conditions in many poor communities in the U.S.


Psychosocial Stress

Ideally, the body is in homeostatic balance, a state in
which the vital measures of human function heart rate,
blood pressure, blood sugar levels and so on are in their
optimal ranges. A stressor is anything that threatens to
disrupt homeostasis. For most organisms, a stressor is an
acute physical challenge for example, the need for an
injured gazelle to sprint for its life or for a hungry predator to
chase down a meal. The body is superbly adapted to dealing
with short-term physical challenges to homeostasis. Stores of
energy, including the sugar glucose, are released, and
cardiovascular tone increases to facilitate the delivery of fuel
to exercising muscle throughout the body. Digestion, growth, tissue
repair, reproduction and other physiological processes not
needed to survive the crisis are suppressed. The immune
system steps up to thwart opportunistic pathogens. Memory
and the senses transiently sharpen.

But cognitively and socially sophisticated species, such as
we primates, routinely inhabit a different realm of stress. For
us, most stressors concern interactions with our own species,
and few physically disrupt homeostasis. Instead these psycho-
social stressors involve the anticipation (accurate or other-
wise) of an impending challenge. And the striking
characteristic of such psychological and social stress is its
chronicity. For most mammals, a stressor lasts only a few
minutes. In contrast, we humans can worry chronically over
a 30-year mortgage.

Unfortunately, our body's response, though adaptive for
an acute physical stressor, is pathogenic for prolonged
psychosocial stress. Chronic increase in cardiovascular tone
brings stress-induced hypertension. The constant
mobilization of energy increases the risk or severity of diseases
such as type 2 (adult-onset) diabetes. The prolonged
inhibition of digestion, growth, tissue repair and
reproduction increases the risks of various gastrointestinal
disorders, impaired growth in children, failure to ovulate in
females and erectile dysfunction in males. A too-extended
immune stress response ultimately suppresses immunity and
impairs disease defenses. And chronic activation of the
stress response impairs cognition, as well as the health,
functioning and even survival of some types of neurons.

An extensive biomedical literature has established that
individuals are more likely to activate a stress response and
are more at risk for a stress-sensitive disease if they (a) feel
as if they have minimal control over stressors, (b) feel as if
they have no predictive information about the duration and
intensity of the stressor, (c) have few outlets for the
frustration caused by the stressor, (d) interpret the stressor as
evidence of circumstances worsening, and (e) lack social
support for the duress caused by the stressors.

Psychosocial stressors are not evenly distributed across
society. Just as the poor have a disproportionate share of
physical stressors (hunger, manual labor, chronic sleep
deprivation with a second job, the bad mattress that can't be
replaced), they have a disproportionate share of
psychosocial ones. Numbing assembly-line work and an
occupational lifetime spent taking orders erode workers' sense
of control. Unreliable cars that may not start in the morning and
paychecks that may not last the month inflict
unpredictability. Poverty rarely al-lows stress-relieving
options such as health club memberships, costly but relaxing
hobbies, or sabbaticals for rethinking one's priorities. And
despite the heartwarming stereotype of the "poor but loving
community," the working poor typically have less social
support than the middle and upper classes, thanks to the
extra jobs, the long commutes on public transit, and other

Marmot has shown that regardless of SES, the less autonomy one has at
work, the worse one's cardiovascular
health. Furthermore, low control in the workplace accounts
for about half the SES gradient in cardiovascular disease in
his Whitehall population.

Feeling Poor

Three lines of research provide more support for the influence of
psychological stress on SES-related health gradients. Over the past
decade Nancy E. Adler of the University of California, San Francisco,
has explored the difference between objective and subjective SES and
the relation of each to health. Test subjects were shown a simple
diagram of a ladder with 10 rungs and then asked, "In society, where
on this ladder would you rank yourself in terms of how well you're
doing?" The very openness of the question allowed the person to define
the comparison group that felt most emotionally salient.

As Adler has shown, a person's subjective assessment of his or her SES
takes into account the usual objective measures (education, income,
occupation and residence) as well as measures of life satisfaction and
of anxiety about the future. Adler's provocative finding is that
subjective SES is at least as good as objective SES at predicting
patterns of cardiovascular function, measures of metabolism,
incidences of obesity and levels of stress hormones -- suggesting that
the subjective feelings may help explain the objective results.


Sidebar: The Good and Bad Effects of Stress

The human body is superb at responding to the acute stress of a
physical challenge, such as chasing down prey or escaping a predator.
The circulatory, nervous and immune systems are mobilized while the
digestive and reproductive processes are suppressed. If the stress
becomes chronic, though, the continual repetition of these responses
can cause major damage.

Acute stress:
Increased alertness and
less perception of pain

Chronic stress:
Impaired memory and
increased risk of depression

Acute stress:
Thymus Gland and
Other Immune Tissues
Immune system readied for
possible injury

Chronic stress:
Thymus Gland and
Other Immune Tissues
Deteriorated immune

Acute stress:
Circulatory System
Heart beats faster, and
blood vessels constrict to
bring more oxygen
to muscles

Chronic stress:
Circulatory System
Elevated blood pressure
and higher risk of
cardiovascular disease

Acute stress:
Adrenal Glands
Secrete hormones that
mobilize energy supplies

Chronic stress:
Adrenal Glands
High hormone levels slow
recovery from acute stress

Acute stress:
Reproductive Organs
Reproductive functions are
temporarily suppressed

Chronic stress:
Reproductive Organs
Higher risks of infertility
and miscarriage


This same point emerges from comparisons of the SES/health gradient
among nations. A relatively poor person in the U.S. may objectively
have more financial resources to purchase health care and protective
factors than a relatively wealthy person in a less developed country
yet, on average, will still have a shorter life expectancy. For
example, as Stephen Bezruchka of the University of Washington
emphasizes, people in Greece on average earn half the income of
Americans yet have a longer life expectancy. Once the minimal re-
sources are available to sustain a basic level of health through
adequate food and housing, absolute levels of income are of remarkably
little importance to health. Although Adler's work suggests that the
objective state of being poor adversely affects health, at the core of
that result is the subjective state of feeling poor.

Being Made to Feel Poor

Another body of research arguing that psychosocial factors mediate
most of the SES/health gradient comes from Richard Wilkinson of the
University of Nottingham in England. Over the past 15 years he and his
colleagues have reported that the extent of income inequality in a
community is even more predictive than SES for an array of health
measures. In other words, absolute levels of income aside, greater
disparities in income between the poorest and the wealthiest in a
community predict worse average health. (David H. Abbott of the
Wisconsin National Primate Research Center and I, along with our
colleagues, found a roughly equivalent phenomenon in animals: among
many nonhuman primate species, less egalitarian social structures
correlate with higher resting levels of a key stress hormone an index
for worse health among socially subordinate animals.)


Sidebar: The surest way to feel poor

The surest way to feel poor is to be endlessly made aware of the haves
when you are a have-not.


Wilkinson's subtle and critical finding has generated considerable
controversy. One dispute concerns its generality. His original work
suggested that income inequality was relevant to health in many
European and North American countries and communities. It has become
clear, however, that this relation holds only in the developed country
with the greatest of income inequalities, namely, the U.S.

Whether considered at the level of cities or states, income
inequality predicts mortality rates across nearly all ages in the
U.S. [see illustration on opposite page]. Why, though, is this
relation not observed in, say, Canada or Denmark? One
possibility is that these countries have too little income
variability to tease out the correlation.

Some critics have questioned whether the linkage between income
inequality and worse health is merely a mathematical quirk. The
relation between SES and health follows an asymptotic curve: dropping
from the uppermost rung of society's ladder to the next-to-top step
reduces life expectancy and other measures much less drastically than
plunging from the next-to-bottom rung to the lowest level. Because a
community with high levels of income inequality will have a relatively
high number of individuals at the very bottom, where health prospects
are so dismal, the community's average life expectancy will inevitably
be lower than that of an egalitarian community, for reasons that have
nothing to do with psychosocial factors. Wilkinson has shown, however,
that de-creased income inequality predicts better health for both the
poor and the wealthy. This result strongly indicates that the
association between illness and inequality is more than just a
mathematical artifact.

Wilkinson and others in the field have long argued that the more
unequal income in a community is, the more psychosocial stress there
will be for the poor. Higher income inequality intensifies a
community's hierarchy and makes social support less avail- able: truly
symmetrical, reciprocal, affiliative support exists only among equals.
Moreover, having your nose rubbed in your poverty is likely to lessen
your sense of control in life, to aggravate the frustrations of
poverty and to intensify the sense of life worsening.

If Adler's work demonstrates the adverse health effects of
feeling poor, Wilkinson's income inequality work suggests
that the surest way to feel poor is to be made to feel poor to
be endlessly made aware of the haves
when you are a have-not. And in our
global village, we are constantly
made aware of the moguls and
celebrities whose resources dwarf

John W. Lynch and George A. Kaplan of the University of Michigan at
Ann Arbor have recently proposed another way that people are made to
feel poor. Their "neomaterialist" interpretation of the income
inequality phenomenon which is subtle, reasonable and, ultimately,
deeply depressing runs as follows: Spending money on public goods
(better public transit, universal health care and so on) is a way to
improve the quality of life for the average person. But by definition,
the bigger the income inequality in a society, the greater the
financial distance between the average and the wealthy. The bigger
this distance, the less the wealthy have to gain from expenditures on
the public good. Instead they would benefit more from keeping their
tax money to spend on their private good a better chauffeur, a gated
community, bottled water, private schools, private health insurance.
So the more unequal the income is in a community, the more incentive
the wealthy will have to oppose public expenditures benefiting the
health of the community. And within the U.S., the more income
inequality there is, the more power will be disproportionately in the
hands of the wealthy to oppose such public expenditures. Ac-cording to
health economist Evans, this scenario ultimately leads to "private
affluence and public squalor."

This "secession of the wealthy" can worsen the SES/health
gradient in two ways: by aggravating the conditions in low-
income communities (which account for at least part of the
increased health risks for the poor) and by adding to the
psychosocial stressors. If social and psychological stressors
are entwined with feeling poor, and even more so with
feeling poor while being confronted with the wealthy, they
will be even more stressful when the wealthy are striving to
decrease the goods and services available to the poor.

Social Capital

A third branch of support for psychosocial explanations
for the relation between income inequality and health comes
from the work of Ichiro Kawachi of Harvard University,
based on the concept of "social capital." Although it is still
being refined as a measure, social capital refers to the broad
levels of trust and efficacy in a community. Do people
generally trust one another and help one another out? Do
people feel an incentive to take care of commonly held re-
sources (for example, to clean up graffiti in public parks)?
And do people feel that their organizations such as unions
or tenant associations actually have an impact? Most studies
of social capital employ two simple measures, namely, how
many organizations people belong to and how people answer
a question such as, "Do you think most people would try to
take advantage of you if they got a chance?"

What Kawachi and others have shown is that at the levels
of states, provinces, cities and neighborhoods, low social
capital predicts bad health, bad self-reported health and high
mortality rates. Using a complex statistical technique called
path analysis, Kawachi has demonstrated that (once one
controls for the effects of absolute income) the strongest
route from income inequality to poor health is through the
social capital measures to wit, high degrees of income
inequality come with low levels of trust and support, which
increases stress and harms health.

None of this is surprising. As a culture, America has
neglected its social safety nets while making it easier for the
most successful to sit atop the pyramids of inequality. More-
over, we have chosen to forgo the social capital that comes
from small, stable communities in exchange for unprecedented
opportunities for mobility and anonymity. As a result, all
measures of social epidemiology are worsening in the U.S. Of
Westernized nations, America has the greatest income in-
equality (40 percent of the wealth is controlled by 1 percent
of the population) and the greatest discrepancy between
expenditures on health care (number one in the world) and
life expectancy (as of 2003, number 29).

The importance of psychosocial factors in explaining the
SES/health gradient generates a critical conclusion: when it
comes to health, there is far more to poverty than simply not
having enough money. (As Evans once stated, "Most graduate
students have had the experience of having very little money,
but not of poverty. They are very different things.") The
psychosocial school has occasionally been accused of
promulgating an antiprogressive message: don't bother with
universal health care, affordable medicines and other salutary
measures because there will still be a robust SES/health gradient
after all the reforms. But the lesson of this research is not to
abandon such societal change. It is that so much more is

Additional Reading:

Wilkinson, Richard. Mind the Gap: Hierarchies, Health and Human
Evolution. London, UK: Weidenfeld and Nicolson, 2000.

Kawachi, Ichiro and Bruce P. Kennedy, The Health of Nations: Why
Inequality Is Harmful to Your Health. New York: New Press, 2002.

Marmot, Michael. The Status Syndrome. New York: Henry Holt and
Company, 2004.

Sapolsky, Robert. Why Zebras Don't Get Ulcers: A Guide to Stress,
Stress-Related Diseases and Coping. Third edition. New York: Henry
Holt and Company, 2004.


Robert Sapolsky is professor of biological sciences, neurology and
neurological sciences at Stanford University and a re-search associate
at the National Museums of Kenya. In his lab- oratory work, he focuses
on how stress can damage the brain and on gene therapy for the nervous
system. In addition, he studies populations of wild baboons in East
Africa, trying to determine the relation between the social rank of a
baboon and its health. His latest book is Monkeyluv and Other Essays
on Our Lives as Animals (Scribner, 2005).