The link between poverty, poor health and lower life expectancy is well-established. Likewise, chronic illness is more likely to make one poor, although this goes only a very small way to explain the strength of an association documented across the world.
The association exists even in countries like Australia, which make available the finest healthcare regardless of wealth. It is particularly stark in the Australian setting because of the high prevalence of illness among the Indigenous population, where life expectancy for men is 17 years less than the national average. Although Indigenous health has particular challenges, the fundamental causes are probably similar to those affecting lower socio-economic individuals in general.
One of the most comprehensive studies of health differences based on income and status in Western societies is the Whitehall Study, which began in 1967. It involved examining thousands of British civil servants whose job classification corresponded closely with their income and position on a socio-economic spectrum. Those at the bottom of the pile, such as messengers and guards, had a mortality rate three times higher than the senior executives at the top. Somewhat less than half of the difference was explained by the most important and well-recognised predictors of illness such as untreated high blood pressure, high cholesterol levels or (importantly) a higher frequency of smoking.
Research similar to the British study has shown that health varies by social status and income even in societies where income as a whole is high and those with the lowest socio-economic status would not be considered poor elsewhere in the world. This has led to a greater focus on the ways relative poverty and low social status can lead to illness. A complex web of factors including stress, mistreatment, depression, poor coping skills and lesser health literacy appears likely to underpin poor health-related behaviours including diet, higher smoking prevalence and less attention to preventive health. Possibly other yet undiscovered pathways may also play a part.
The role of stress received particular attention as a result of the British findings. A strong correlation between low employment status, domestic stress and poor self-esteem suggests job stress may be only one component, with the flow-on to other aspects of life equally if not more important. Financial insecurity is one potent cause of domestic stress, with those affected tending to have the worst coping skills. Stressed or depressed individuals are hardly likely to prioritise preventive health over other aspects of their life.
With an increased appreciation of the role of socio-economic factors affecting health behaviours it might have been expected that progress would follow in reducing the disparities.
In this respect, a recent study looking at cardiovascular disease risk factors in the US is disappointing. It shows that while cholesterol levels fell similarly across the socio-economic spectrum between 1999 and 2014, blood pressure control and smoking had not improved among the least affluent. Although the findings’ relevance to countries with more comprehensive systems of healthcare is unclear, they suggest that improving the health of the least affluent is not necessarily a straightforward task.
Until recently, much of the impact of socio-economic health differences was on heart disease rates. The community-wide incidence of heart disease, however, has been falling sharply relative to cancer and external causes of death (mainly suicide and trauma). Apart from smoking-related malignancies, the incidence of cancer overall is less affected by socio-economic factors, with some types of cancer more common among higher socio-economic cohorts.
This could change. Controlling cancer will increasingly involve screening for early detection and/or the use of expensive drugs as a part of treatment regimens. To avoid socio-economic disparities emerging in cancer outcomes, it will be necessary to explicitly target the less well-off for screening and ensure equitable access to effective therapies.
Finally, it is important to recognise that illness and mortality patterns can change rapidly and sometimes these can add even more to the socio-economic gradients of health. This has been seen in the US, where deaths from opiate misuse and suicide have risen sharply among men of lower socio-economic status. It provides another demonstration that the imperative to reduce socio-economic-related health differences will require attention to a broad range of social and public health factors.