2c. Income and the Social Gradient

Income is arguably the most important social determinant of health affecting the health status of populations. To fully appreciate the impact of income as a predictor of health status, the relationship between income and health needs to be examined at two different levels. First, a large body of evidence indicates that health outcomes are contingent upon the actual income that an individual or family receives. Second, the equality of income distribution across a society has proven to be one of the best predictors of better overall population health.^1,2,3

Low income predisposes people to material and social deprivation, making it more challenging to afford the basic prerequisites of health such as food, clothing, and housing. Deprivation also contributes to social exclusion by making it harder to participate in cultural, educational, and recreational activities. Ultimately, this deprivation results in higher levels of morbidity and mortality.

For example, a Canadian study found that men in the wealthiest 20% of neighbourhoods in Canada live on average more than four years longer than men in the poorest 20% of neighbourhoods, and the comparative difference for women was almost two years (see Figure 1).⁴

The study also found that those living in the most economically disadvantaged neighbourhoods had death rates that were 28% higher than the least disadvantaged neighbourhoods. ⁴

However, the impact of socio-economic status on health extends beyond those experiencing the stress arising from living in poverty. The social gradient in health refers to the fact that inequalities in population health status are related to corresponding inequalities in social status.⁵

One of the first detailed cohort studies examining the impact of the social gradient on health was the Whitehall I study, a ten-year prospective cohort study of over 18 000 British male civil servants aged 20–64.^6,7 The study played a pivotal role in focusing attention on social organization as a mechanism contributing to health inequities. 

As Figure 2 illustrates, Whitehall I showed that mortality — both from coronary heart disease (CHD) and all causes — was higher among those in the lower grades of employment when compared to the higher grades. The more senior one’s position in the civil service hierarchy, the longer one might expect to live compared to people in lower employment grades.⁶

The study identified several risk factors for coronary heart disease (CHD) that were higher for men at lower grades of employment than for those at higher grades, including higher BMI, higher blood pressure, higher rate of smoking, and less physical activity during leisure time. However, about 60% of the difference in mortality between those at lower and higher grades of employment could not be accounted for by the medical risk factors measured in the study.⁶

More recent analyses have illustrated how the social gradient resulting from the unequal distribution of income can affect health status. Wilkinson and Pickett (2010) compiled data from all advanced industrialized nations to explore the relationship between levels of income inequality and performance in key health and social indicators, including life expectancy, infant mortality, and obesity.³ The authors consistently found that countries with higher levels of income inequality had higher levels of health and social problems (e.g., drug use, imprisonment), across all income levels. Simply living in a more unequal society puts individuals at greater risk of negative health outcomes.

As was noted earlier, equitable access to the SDH are shaped by the distribution of money, power, and resources at global, national, and local levels.

The following lecture by Dr. Dennis Raphael provides more information on the political economy of health inequalities.