Income inequality and mortality: why are they related?

Income inequality goes hand in hand with underinvestment in human resources

The long held belief that household income is an important indicator of risk of death has recently received strong support from a series of large prospective studies.1 2 Income inequality within a population has also been suggested to be an important determinant of population mortality. In a cross national comparison, Rodgers found associations between income inequality and three mortality indicators—infant mortality, life expectancy at birth, and life expectancy at age 5—after taking overall gross national product into account.3 Several replications of this, across both a wide range of countries and within industrialised nations alone, using a variety of health indicators, have appeared.4 5 6 7 These studies have related income inequality to infant mortality,4 life expectancy,5 height,6 and morbidity,7 with a consistent finding that the less equitable the income distribution in a country, the less favourable the health outcome.

In this week's issue of the BMJ, two studies relate income inequality between states in the United States to mortality rates within these states. Kennedy and colleagues (p 1004) show that greater income inequality is associated with higher mortality from several broad causes of death, although taking levels of poverty and smoking prevalence into account attenuates these associations.8 Kaplan et al find associations between level of inequality and mortality in both 1980 and 1990 (p 999), with trends in mortality differences between states over this decade being inconsistently related to changes in income inequality.9

In Britain, reliable data on income inequality by area are not readily available. Also in this issue, Ben-Shlomo et al (p 1013) have used the variation in small area deprivation scores within local authority areas in Britain as their …