Under the Microscope: There is a close connection between socio-economic status (SES) and health. The better your SES, the better your prospects for good health, writes Prof William Reville.
The conventional explanations, such as poor people having less access to healthcare and engaging to a greater extent in harmful lifestyles, only account for a minor fraction of their relatively poorer health. New research attributes the bulk of the discrepancy in health outcomes to psychosocial stress associated with poverty. This work is reviewed by Robert Sapolsky in Scientific American, December 2005.
It is now well-established that better health is associated with higher income, better education and prestigious employment, as well as with living in a neighbourhood where a higher proportion of residents have higher income and better education. Starting with the best-off sector of society, every step downwards in SES correlates with poorer health, including respiratory and cardiovascular problems, rheumatoid disorders, ulcers, psychiatric problems and some cancers. Startling differences are noted between the highest and lowest SES categories (in the US, for example, the richest white males live 10 years longer on average than the poorest).
SES is remarkably predictive of health as illustrated by a study of elderly American nuns. They all entered orders as young adults and subsequently spent many years sharing the same diet, housing and healthcare. In their old age their patterns of disease, dementia and longevity were still reliably predicted by their SES status on entering the convent 50 years previously.
A landmark study by Michael Marmot - The Status Syndrome (Henry Holt, 2004) - of British civil servants over three decades found that messengers and porters, for example, are much more likely to die of heart disease than administrators and professionals. All have good access to UK healthcare and the correlation remains strong even when account is taken of the rate of usage of medical services.
The traditional explanations of the SES health gradient include (a) that healthcare for the poor may be difficult to access and of poor quality, and (b) that poorer people tend to have less healthy lifestyles, involving smoking, excessive alcohol consumption, obesity and living in violent or polluted areas. However, studies controlling for such factors show that they account for only about one-third of the SES health discrepancy.
There is considerable evidence now that the SES health gradient is largely explained in developed countries by the psychosocial stress experienced by poorer people. Our bodies are well-equipped by evolution to deal with acute physical stress (eg, the flight-or-fight response). If you are suddenly confronted with an aggressive dog, you have to decide immediately whether to run or to fight. Your body instantly and automatically responds hormonally to mobilise energy reserves, increase cardiovascular tone and temporarily suppress physiological processes not vital to dealing with the crisis. The stress usually lasts a few minutes and the body then quickly returns to a normal, healthy, resting condition.
However, stress in the cognitive social life of humans is often chronic. For example, no animal will worry year-in-year-out about the behaviour of an errant offspring or an overbearing boss, but this can easily happen in human situations. Chronic stress keeps the body in an ongoing state of hormonal arousal which is maladaptive and increases the risk of many diseases, including cardiovascular problems, diabetes, gastrointestinal disorders, reproductive disorders, impaired memory and depression. Amazingly, Marmot's study of civil servants shows that low control in the workplace accounts for half the SES gradient in cardiovascular disease.
Just as physical stresses such as hunger, exposure to the elements, hard manual work, and so on, are not distributed evenly across society, neither are psychosocial stresses, which increase the lower down the psychosocial ladder you go. Other research has shown that, objective criteria aside, if you feel that you are low on the SES scale this has the same effect on your health prospects as if you are objectively low on the scale. And, if you feel you are higher on the SES scale, this works in the opposite direction. Greeks on average have half the income of Americans, yet have a longer life expectancy.
A steep gradient of income inequality in a society seems to be particularly corrosive, increasing psychosocial stress and its consequent ill-health prospects in the less well-off. This effect is particularly strong in the US but, thankfully, is greatly ameliorated in European social welfare states. The American situation is exacerbated by aggressive advertising of material goods and the manner in which many rich people flaunt their wealth, making less well-off people, who may not be that poorly off objectively, feel poor.
These insights into the effects of psychosocial factors on public health are of the greatest importance. They are counter-intuitive and, to date, have had little influence on public health interventions despite the fact that they are of significantly more importance than the targets traditional interventions are aimed at, such as the amelioration of physical stressors.
The more egalitarian and less polarised our society becomes, the better for our health. But interventions to flatten things out could only go so far before becoming counter-productive. There is much natural variety and range of ability in people, which must not be frustrated.
However, the simple conclusion seems to be that the more acquisitive, stratified and competitive our society becomes, the higher the toll exacted in ill-health. We need to have a word in the Celtic Tiger's ear.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC (http://understandingscience.ucc.ie)